VADD_sightandlife

SIGHT AND LIFE MANUALON

VITAMIN ADEFICIENCY DISORDERS

(VADD)

by

Donald S. McLaren, MD, PhD, FRCP

Honorary Head, Nutritional BlindnessPrevention Programme, International Centre

for Eye Health, London, UK

and

Martin Frigg, PhD

Secretary, Task Force SIGHT AND LIFEPO Box 2116, 4002 Basel, Switzerland

Second Edition2001

ISBN 3-906412-03-2

© Task Force SIGHT AND LIFEPO Box 21164002 BaselSwitzerlandPhone: +41 61 688 7494Fax: +41 61 688 1910E-mail: [email protected] information:http://www.sightandlife.org

Layout and cover design: Martin Frigg

Acknowledgements

The authors thank Alfred Sommer and Keith West as well as Oxford University Press forpermission to reproduce tables and figures from the book Vitamin A Deficiency, Health, Sur-vival, and Vision. Thanks also go to Rune Blomhoff for Figures 3.2, 3.3, 3.4, 3.6 and 3.7; toThomas Rohrer and Marion Segato for technical assistance in creating many of the figures; toWHO for the updates of Figures 8.1 to 8.7 and Table 8.1 by October 2000, and to FranziskaHorat for proof-reading.

We received valuable comments on the review version of the Manual from Alfred Sommer,Keith West, Florentino Solon, Martin Suter, Kurt Bernhard, Jochen Bausch, Clare Gilbert,Clive West, Otto Raunhardt and Hanspeter Pfander.

SIGHT AND LIFE MANUAL

III

FOREWORD TO THE SECOND EDITION

Roche founded the Task Force SIGHT ANDLIFE in 1986 to participate actively in the fightagainst preventable blindness. SIGHT ANDLIFE is dedicated to the prevention and eradi-cation of xerophthalmia and all forms ofvitamin A deficiency that impair children’shealth in developing countries.

SIGHT AND LIFE is supporting a broadrange of efforts aiming at preventingvitamin A-related blindness and child mortal-ity in developing countries. One of the mainactivities is to donate vitamin A capsules forrapid intervention, but the Task Force alsoprovides educational material, supports re-search projects and gives technical assist-ance. It helps funding projects and provideseducational grants. With its Newsletter,SIGHT AND LIFE is offering a platform forthe dialogue of experts engaged in the fightagainst vitamin A deficiency. The publicationis covering all relevant topics from most ad-vanced scientific findings in biochemistry tothe practical problems of teaching gardeningof green leafy vegetables in remote areas.

This handbook is the latest in the diverserange of information tools produced over thelast few years by SIGHT AND LIFE. Its pri-mary aim is to present the knowledge con-tained in existing lecture and pictorial mate-rial, some of which has been reworked, in aform that practitioners can put to direct use.The result is a handbook for those working inthe “vitamin A front line” in developing coun-tries who need an information tool thatpresents the complexities in a clear and un-

derstandable fashion without trivializing oroversimplifying the issues. Particularly whenused together with the slide set, the hand-book will serve as an aid to further educationand in prevention campaigns.

In Professor Donald S. McLaren we areextremely fortunate to have found an authorwhose profound knowledge and many yearsof experience have made him an internation-ally recognized expert. Dr Martin Frigg, Sec-retary of SIGHT AND LIFE, contributed theTask Force’s fund of accumulated know-howto the publication and helped ensure that thepresentation of the material was geared tothe needs of the target audience.

Three years after the initial publication, al-most 5000 copies of the SIGHT AND LIFEManual have found their way to an interestedpublic of specialists all over the world. It isquite encouraging to see that after such arelatively short time a second, revised editionwas necessary: It clearly shows, better thanmany words, that the body of knowledge onvitamin A deficiency, how it affects people andhow it can be fought has grown very fast. Andthe publication of a thoroughly revised sec-ond edition also shows the determination ofboth authors to share all these new insightswith everybody willing to be part of the effortsto reduce vitamin A deficiency disorders allover the world.

Dr Andres F. LeuenbergerChairmanTask Force SIGHT AND LIFE


V

The reader of this book should know at thebeginning something of the purpose forwhich it has been written. It is designated aManual, or Handbook, and indeed is in-tended to be the kind of book that will be “athand” as a guide to those interested in andworking in this field. There was a time whensuch a book might be called a Vade Mecum– “come with me”, a companion for study.

For those lecturing and communicatingabout vitamin A, a slide collection and theaccompanying notes have also been pre-pared for SIGHT AND LIFE at the sametime. These are designed to amplify theother material, just as the notes enlarge onthe topics that can only be hinted at in theslide presentation.

The Manual takes a very practical ap-proach, dealing with those problems that areof concern to health and nutrition workers,especially those in the fields of child sur-vival and protection of vision. If read throughchapter by chapter it will provide a compre-hensive and up-to-date account of the sub-ject. The Manual may also be used, to someextent, as a reference text and to assist thisprocess a detailed Table of Contents andIndex are provided. However, it has not

been the intention that the information pro-vided should be considered to be exhaus-tive. The story of vitamin A and carotenoidsin nature, of the consequences to man ofconsuming a deficient diet, and of the meas-ures now being taken to eradicate the prob-lem is a fascinating one. It is hoped thatmany readers will have their appetites whet-ted to delve much more deeply into the sub-ject. For those readers, in addition to thekey references that appear in alphabeticalorder at the end of the book, a short list ofpublications for further reading has beenprovided.

It will also prove helpful to the reader atthe outset to appreciate the reasoning be-hind the choice of the title of the Manual.The term Vitamin A Deficiency (VAD) em-braces all forms and degrees of deficiency,including the most severe, in which the func-tion and structure of the eye are affected.All stages of the eye changes are coveredby the term Xerophthalmia (X). It is only inthe past two decades or so that the threatto health and survival of lesser degrees ofVAD has become apparent. Those respon-sible for setting up SIGHT AND LIFE atRoche are to be commended for their in-sight when they named it in this way, cov-

PREFACE TO THE FIRST EDITION

VI


ering the implications for morbidity and mor-tality of milder degrees of VAD, but also in-cluding X, which itself embraces the blind-ing consequences of severe deficiency.

It is now becoming increasingly apparentthat VAD is responsible for a wide varietyof disorders. Vitamin A Deficiency Disorders(VADD) is proposed as a comprehensiveterm to cover all aspects of the deficiencystate.

So it is that interest in a relatively uncom-mon blinding disease of children (albeit stillthe most common cause of blindness world-wide in that age group) that was primarilythe responsibility of ophthalmologists andpaediatricians has expanded in recent yearsto include concern about one of the majorpublic health factors in developing countriesthreatening survival and well-being in youngchildren and other vulnerable groups.

We commence our study with considera-tion of the roles played in nature by vitamin Aand its precursor carotenoids and learn howthe chemical and physical characteristics oftheir molecular structure largely determinetheir functions. Of central importance for ourpurposes is knowledge about the foodsources, both vegetable and animal, ofvitamin A, and these are considered insome detail, together with the various fac-tors that may influence the concentration ofnutrients and their availability from the diet.Ultimately a lasting solution to the problemof VADD can only come by ensuring thatthe dietaries of those at risk provide ad-equate vitamin A for their needs.

We then turn our attention to what hap-pens to vitamin A in the body once it hasbeen ingested and to what we know abouthow it fulfils its various functions at the mo-lecular level, an area of knowledge that is

the subject of intense research. This leadslogically to the need for a balance to bestruck between the body’s requirements forvitamin A to carry out the various functionsunder a variety of conditions and the intakefrom the diet. These requirements are cus-tomarily expressed in terms of Recom-mended Dietary Allowances (RDA). As aprelude to discussion of VADD itself in itsvarious forms, there then follows an accountof the existing methodologies for the as-sessment of vitamin A status and their ap-plication for drawing up guidelines for de-fining the existence and extent of a prob-lem of VAD. Recently much attention hasbeen given to the development of indica-tors for assessing subclinical VAD and it willbe necessary to point out some of the diffi-culties being encountered in this complexfield.

There then follow three chapters that de-scribe the ocular manifestations of vitamin Adeficiency (xerophthalmia), the contributionof VAD to mortality and morbidity, especiallyin young children, and its at present onlypartially understood role in growth retarda-tion, impairment of the immune response,defective haemopoiesis and some other dis-orders. Two further chapters describe theglobal prevalence of VADD, actively underreview by the World Health Organization,and its epidemiology.

The final section is devoted to the all-im-portant subject of the control of VADD. Thisis dealt with under seven headings – treat-ment, prophylaxis, prevention and manage-ment of infectious diseases, fortification,dietary modification, plant breeding, anddisaster relief.

Finally, we are very grateful to all thoseauthors of the original work which we haveused and for their contribution to this en-


VII

deavour. In particular it will be evident howdependent we have been on the timely pub-lication of the monumental book Vitamin ADeficiency: Health, Survival, and Vision byAlfred Sommer and Keith West of JohnsHopkins University. Where for our purposestables or figures have been simplified, read-

ers requiring full particulars should refer tothe original sources, which are cited here.It would be appreciated if readers would in-form us of any errors they may come across.The intention is to keep the Manual underregular revision and updating, and sugges-tions in this regard would be welcome.

Donald S. McLaren and Martin Frigg

PREFACE TO THE SECOND EDITION

The first edition of the SIGHT AND LIFEManual on Vitamin A Deficiency Disorders(VADD) was produced in September 1997.Just over three years later this second edi-tion is appearing. During that relatively shorttime supplies of the earlier edition have beenexhausted, and many people have been ableto read the Manual in their own language, inSpanish with widespread distribution in LatinAmerica and in Chinese. The translation intoFarsi is ready to be printed, and this secondedition is being translated into French. Othertranslations may appear in the future. TheSlide Set issued in more limited fashion atthe same time has also been widely appreci-ated.

There are several reasons why a new andrevised edition would appear to be justifiedat this time. In certain sections in particular,advances in recent years have been so great

that the information had to be considered tobe seriously out of date. For example, it hasrecently become much better understood ex-actly how vitamin A carries out its varied func-tions in virtually every part of the body. In thecell nucleus acid compounds of vitamin A (all-trans retinoic acid and other related retinoids)bind to and activate specific nuclear receptorsto induce or repress hundreds of genes.These retinoids are now recognized to havethe functions of a hormone belonging to whathas been termed the Steroid-Thyroid-RetinoidSuperfamily.

The complexity of the many factors deter-mining the bioavailability of provitamin Acarotenoids in the body is only now begin-ning to be appreciated. Techniques have re-cently been developed which enable the de-termination with some accuracy of the frac-tion of ingested carotenoid that is available

for utilization by the body. In general it ap-pears that estimations in the past have beenover-optimistic and this seems to have beenespecially true in the case of dark green leafyvegetables. These have been regarded as themainstay of the approach to the improvementof the intake of vitamin A from vegetablesources in developing countries. This clearlyhas important implications for the design ofdietary interventions.

During this time too attention has beendrawn to the potential importance of vitaminA and β-carotene supplementation duringpregnancy to maternal health and survival andalso to that of the fetus and very young in-fant. It has become quite clear that strongeremphasis needs to be given to the role of vi-tamin A status in the area of maternal as wellas child health. In the first edition only pass-ing reference was made to those aspects ofvitamin A and carotenoid metabolism that donot refer directly to VADD. Research in someof these areas has recently increased to suchan extent that a new chapter on “Vitamin A ingeneral medicine” has been included. Thischapter covers topics such as secondary orendogenous vitamin A deficiency, hypervita-minosis A, therapeutic use of retinoids, andthe role of non-provitamin and provitamin

carotenoids in the prevention and treatmentof diseases such as cancer, heart disease andsome eye diseases.

Finally, we have tried to accede to the re-quest of some readers that the final chapteron control of VADD be given greater promi-nence. After all this is the focus and climax ofall the effort that has been building up sincethe early days when eventually the interna-tional community acknowledged that therewas a serious problem and set about tack-ling it.

The opportunity to revisit this theme hasbeen an enlightening and encouraging ex-perience. It is good to know that researchand intervention efforts in this field con-tinue unabated. The reader will find here awide range of challenges to both head andheart. The wonders of the colours in theworld around us will take on new meanings.The intricacies of the fundamental processesof life will never cease to amaze. The need-less destruction and blighting of innocentlives through the lack of a few units of a vita-min on display all around us will continue tomove our hearts and hands until the needhas been ended.

Donald S. McLaren and Martin Frigg

October 2000


IX

FOREWORD IIIPREFACE VCONTENTS IX

Chapter 1VITAMIN A IN NATURE 1

Introduction 1Occurrence of carotenoids 1Occurrence of vitamin A 3

Chemistry 5Carotenoids 5Vitamin A 7

Methods of analysis 8Analytical procedures 8Bioassay procedures 8Carotenoid analysis in foods 8

Chapter 2FOOD SOURCES 9

Units of vitamin A activity 10Provitamin A carotenoid sources 10

Vegetables 11Fruits 12Roots and tubers 12Vegetable oils 12Other sources 13

Bioavailability of carotenoids 15Factors affecting bioavailability 16“S”pecies of carotenoids 16Molecular “L”inkage 17“A”mount of carotenoidsconsumed in a meal 17“M”atrix in which the carotenoidis incorporated 17

CONTENTS

“E”ffectors of absorption andbioconversion 18“N”utrient status of the host 18“G”enetic factors 18“H”ost-related factors 18Mathematical “i”nteractions 18Remarks 18

Preformed vitamin A 19

Chapter 3VITAMIN A IN HEALTH 21

Digestion and absorption 21Transport to the liver 23Metabolism in the liver 23Transport to other cells 25Cellular uptake 28Cellular retinoid-binding proteins 28Gene function and retinoids 28Functions of vitamin A 30

Vision 30Cellular differentiation 32Glycoprotein and glycosamino-glycan synthesis 33Embryogenesis 33Immune response, Reproduction,Haemopoiesis, Growth 34

Other functions 35Energy balance 35Regulation of thedopaminergic system 35Gap junctional communication 35Activities of carotenoids 35

Human requirements 36

X


Chapter 4ASSESSMENT OF VITAMIN ASTATUS 37

Introduction 37Indicators for the assessment ofvitamin A status at the subclinicallevel 40

Serum retinol 40Serum retinol-binding protein (RBP)40RBP/TTR molar ratio 41RAG hydrolysis test 41

Assessment of body reserves 41Indirect assessment of liver stores 42Relative dose response (RDR) 42Modified relative dose response(MRDR) 42Serum 30-day dose response(+S30DR) 42

Advantages 42Disadvantages 42

Recommendations and comments 43Deuterated-retinol-dilutiontechnique 43

Breast milk vitamin Aconcentration 43Histological indicator [ConjunctivalImpression Cytology (CIC)] 44

Limitations 44Impaired dark adaptation 44

Night blindness 46Vision restoration time (VRT) 46Pupillary threshold 47

Assessment of dietary intake ofvitamin A 47Ecological indicators 48

Chapter 5XEROPHTHALMIA 51

Definitions 51Background 52Night blindness (X1N) 53Conjunctival xerosis (X1A) 57Bitot’s spot (X1B) 58Corneal xerosis (X2) 59Keratomalacia (X3A, X3B) 60

Corneal scar (XS) – vitamin A-related 60Xerophthalmic fundus (XF) 62Remarks 62

Chapter 6MORTALITY AND MORBIDITY 63

Introduction 63Mortality associated with non-corneal xerophthalmia 63Vitamin A intervention andmortality in young children 64Cause-specific mortality 66Contribution of vitamin Adeficiency to child mortality 66

Measles mortality andvitamin A treatment 69

Vitamin A supplementationand maternal mortality 71Vitamin A supplementationand infectious morbidity 71

Diarrhoeal diseases 72Respiratory diseases 72Measles 74HIV/AIDS 76Malaria 76Other infections 77

Urinary tract 77Otitis media 77

Meningococcal disease 77Remarks 77

Chapter 7OTHER EFFECTS OF VITAMIN ADEFICIENCY 79

Introduction 79Growth 79Immune response 81Interaction of iron and vitamin A 83Interaction of zinc and vitamin A 85Normal and diseased skin 86Reproductive systems 86Other systems 86


XI

Chapter 8GLOBAL OCCURRENCE 87

Introduction 87Global occurrence 87Methodology 97Country situations 98Introduction 101

Chapter 9EPIDEMIOLOGY 101

Age 101Physiological status 102Diet 103Breast-feeding 104Cultural factors 104Infectious diseases 105

Systemic infections 105Diarrhoeal diseases 106Intestinal parasites 106Respiratory diseases 106Measles and associatedconditions 107

HIV/AIDS 108Protein-energy malnutrition(PEM) 108Season 108Socio-economic status 109Location 110Sex 111The Vitamin A DeficiencyDisorders (VADD) cycle 114

Chapter 10RETINOIDS IN GENERALMEDICINE 115

Introduction 115Secondary VAD 115Non-nutritional diseasesresponsive to vitamin A 116Experimental model ofemphysema 117

Retinitis pigmentosa andsome other retinopathies 117Hypervitaminosis A 117Congenital malformations 118Pharmacological use ofsynthetic retinoids 118

Dermatology 118Cancer chemopreventionand treatment 119

Carotenoids and chronicdiseases 119

The skin 120The eye 120Cancer 120Cardiovascular disease 121

Chapter 11CONTROL 123

Introduction 123Treatment 123Prophylaxis 123Control of infections 124Food fortification 124Dietary interventions 124New plants 124Disaster relief 124

General considerations 124Treatment 125Prophylaxis 126Prevention and managementof infectious diseases 128Food fortification 129Dietary modification 131

General issues 133Plant breeding and geneticmodification 133Disaster relief 134Some country experiences 134

Further Reading 141

Glossary 145

References 147

Index 157


1

compounds within the bodies of most verte-brate animals. These precursors of vitamin Acomprise a small proportion of a large groupof compounds known as carotenoids.

Occurrence of carotenoidsIt will be most instructive for us to commenceour exploration of vitamin A in nature with aconsideration of the much more prevalent anddiverse carotenoids (Karrer, Jucker, 1950).Carotenoids are the most widespread of allgroups of naturally occurring pigments. Theyare red, orange or yellow in colour and arefound in many plants and animals. Natureproduces about 100 million tons of caroten-oid pigments per year. Most of this is fucoxan-

IntroductionStrictly speaking the term Vitamin A shouldbe restricted to the chemical substance all-trans retinol (see Glossary, Cis/trans), but itis justified in the present context to follow aless strict definition. The alcohol, retinol(C20H30O, see Figure 1.1), is usually repre-sented by some closely related forms in na-ture.

Thus it is common practice to say that vita-min A is stored in the liver, or that vitamin A isrequired for the normal functioning of the rodcells in the retina. In actual fact retinyl palmi-tate is the usual storage form of the vitamin,and 11-cis retinal is the very specific form ofvitamin A that acts as the prosthetic group at-tached to the protein opsin to form rhodopsin,or visual purple, required for normal night vi-sion.

In almost all tissues vitamin A functions arecarried out by the acid form, retinoic acid (RA).Specifically this is the all-trans-retinoic acidform, but recently other functional acid de-rivatives have emerged (see p 29). As a re-sult of the recent revolutionary advances inour knowledge of the mechanisms of actionof vitamin A at the cellular level in the form ofRA this compound is now classified as a hor-mone (see p 29).

Vitamin A, in all its closely related forms, isonly present in nature as a result of enzymicaction that takes place on certain precursor

VITAMIN A IN NATURE

Figure 1.1. Formulae of retinol and retinoic acid.

Chapter 1


2

VITAMIN A IN NATURE

thin, the characteristic pigment of many ma-rine brown algae and the most abundant ofall carotenoids. In the leaves of green plantslutein, violaxanthin and neoxanthin are thethree main carotenoids and none is capableof being converted to vitamin A. Until thepresent more than 600 carotenoids, exclusiveof cis-trans isomers, have been isolated andfully characterized. They share commonstructural features, such as the polyisoprenoid

structure and a series of centrally-locatedbonds (Figure 1.2) (Olson, 1994). Most ofthe carotenoids are xanthophylls, which haveone or more oxygen groups on the ring or inthe chain. Xanthophylls are responsible forthe glorious autumnal tints in leaves of de-ciduous trees. Carotenoids of this group alsocontribute to the striking plumage of birdssuch as the cock-of-the-rock, the flamingo andmany others. The attractive colours of many

Figure 1.2. Formulae of some common carotenoids.

VITAMIN A IN NATURESIGHT AND LIFE MANUAL

3

Chapter 1

Table 1.1. Relative provitamin A activity ofvarious carotenoids (Simpson, Tsou, 1986)

Carotenoid Activity (%)

β-carotene 100α-carotene 50–54γ-carotene 42–503,4-dehydro-β-carotene 75β-carotene-5,6-epoxide 21α-carotene-5,6-epoxide 253-oxo-β-carotene 523-hydroxy-β-carotene (cryptoxanthin) 50–604-hydroxy-β-carotene 48β-2'-apo-carotenal activeβ-8'-apo-carotenal 72lycopene inactivelutein inactive3,3'-dihydroxy-β-carotene (zeaxanthin) inactive

red and yellow fruits and vegetables are alsoattributable to their carotenoid content. Theseare only a few of the most evident examplesof carotenoids in nature. They also occur inalgae, fungi, yeasts, moulds, mushrooms,bacteria and in all classes of plants and ani-mals, including mammals. No animal is ableto synthesize carotenoids. Some may alterthem slightly by oxidative metabolism duringdigestion and absorption. Many mammals ac-cumulate carotenoids in their tissues, andthere is recent evidence that this may possi-bly prove to have a function in some rare in-stances (see Chapter 10).

Animals differ greatly in the way thatcarotenoids from their diet accumulate in theirtissues, especially in adipose tissue(Bauerenfeind, 1981). The reason for thesedifferences is not understood. Man accumu-lates carotenoids indiscriminately and they re-main in situ when fat is mobilised as in star-vation. Cattle and horses accumulate mainlycarotenes. Pigs and goats accumulate fewcarotenoids or none. Birds accumulateoxycarotenoids.

Occurrence of vitamin ACertain carotenoids are capable of conver-sion to vitamin A. This is known to occur ininsects, fish, reptiles, birds and mammals.Among the latter, members of the carnivorouscat family do not have this ability. These pro-vitamin A carotenoids, as they are known,number more than 50 and are listed inBauernfeind (p 179, 1981). Of these, all-transb-carotene makes by far the largest contribu-tion to vitamin A activity in foodstuffs. a-caro-tene, g-carotene and b-cryptoxanthin (3-hy-droxy-b-carotene) contribute to a lesser ex-tent.

For provitamin A activity to occur, there arecertain molecular structural requirements. Thecompound must include at least oneunsubstituted β-ionone ring and a polyene

side chain. The other end of the molecule mayhave a cyclic or an acyclic structure. It maybe lengthened but not shortened to less thanan 11-carbon polyene chain. Chain lengthen-ing decreases activity.

Table 1.1 gives a selection of provitamin Aactivities of carotenoids expressed in termsof that of β-carotene, which is considered as100%.

Much interest has recently arisen in theoccurrence and metabolism of 9-cis β-caro-tene. This is because it has been reported tobe a precursor of 9-cis retinoic acid, which isthe ligand for the nuclear retinoid X receptors(see Chapter 3). It has been estimated thatits provitamin A activity may be as high as57% of that of all-trans β-carotene. It ispresent in significant amounts in most dietar-ies but appears to undergo isomerization toa considerable extent before entering the


4

VITAMIN A IN NATURE

plorers and their sled dogs have fallen sickwhen feeding on the liver of these animals.This is an instance of acute hypervitaminosisA or vitamin A toxicity (McLaren, 1993) (seeChapter 10). If large doses of vitamin A orone of the synthetic retinoids are taken dur-ing early pregnancy the fetus may be dam-aged. The subject of safe use of vitamin A isconsidered later (see Chapter 11). Kidney,plasma, milk and those tissues where vita-min A is known to have its main functions,such as the eye and epithelial tissues, havevery low concentrations in comparison withthose found in the liver.

bloodstream. It may therefore not be a richsource of 9-cis retinoids for tissues (You,Parker, Goodman et al, 1996).

The richest sources of vitamin A in natureare livers of some fish, most notably those ofhalibut, cod and shark. Those animals thatare at the end of a long food chain in whichfirst carotenoids and then vitamin A itself areprogressively concentrated at each stagebuild up the highest concentrations. Very highlevels occur in polar bear and bearded sealwithout apparently harming the animal. How-ever, it has long been known that polar ex-

Figure 1.3. Major commercial routes to the synthesis of retinyl acetate (bottom) from, β-ionone (top).The Isler (Roche) procedure is on the left, the Wittig (BASF) method on the right (Olson, 1999).


5

Chapter 1

Vitamin A in liver and other tissues is mainlypresent in esterified form. Pharmaceuticalpreparations which are identical with naturalsources, both chemically and biologically,exist also in the form of fatty acid esters: retinylacetate, propionate or palmitate, which aremore stable than retinol.

In recent years there has been intense in-terest in the therapeutic use of retinoids insome dermatological disorders and their pos-sible prophylactic value in epithelial cancersand other diseases (see Chapter 10).

Vitamin A has been added to a wide vari-ety of foods in order to improve their nutri-tional value (Bauernfeind, 1981). Food forti-fication with vitamin A is one of the measuresavailable for control of VADD (see Chapter11). The major commercial forms are the ac-etate or palmitate esters, which are relativelystable and have high solubility in oils and othercommercial preparations. Esters can be in-corporated into a carrier matrix, e.g. gelatine,which protects them from oxidation as in cook-ing. Such forms have been used frequentlyin food fortification and animal feeds. Undergood storage conditions a high vitamin A ac-tivity is retained for a considerable period oftime.

As a footnote it is of interest that vitamin Ahas been found in the plant kingdom(Stoeckenius, Bogomolni, 1982). The reportof a new retinaldehyde-containing pigment,bacteriorhodopsin, in the membrane of thepurple bacterium Halobacterium halobiumcaused great interest∆ Its basic function is,under the influence of light, to assist in thepumping of protons across membranes, thuspossibly aiding the active transport of nutri-ents. The structure and functions ofbacteriorhodopsin are very similar to thoseof rhodopsin; as are several other related pig-ments in Halobacteria (Olson, 1991).

Chemistry

The structural formulae of β-carotene and vi-tamin A were established by Karrer and col-leagues at the University of Zurich between1928 and 1931. Isler and co-workers, atRoche, were responsible for a commerciallyfeasible synthesis of β-carotene and vitaminA. Karrer was awarded the Nobel prize forchemistry in 1937. Figure 1.3 shows the ma-jor commercial routes for the synthesis ofvitamin A.

Carotenoids (Britton, 1995)

In nature only plants and microorganisms arecapable of synthesizing carotenoids. Acetateis the starting compound. Two molecules ofacetyl-CoA condense to form acetoacetyl-CoA, which coalesces with acetyl-CoA. Afterseveral other steps the important biologicalfive-carbon isoprenoid unit, isopentenyldiphosphate (IDP, see Figure 1.4) is formed.Successive condensations result in ten,twenty, and ultimately forty-carbon units. Thelast of these forms phytoene, from the tail-to-tail linkage of two C20 geranylgeranyl diphos-phate molecules to form the basic 40-carbonacyclic carotenoid structure (see Figure 1.4).

One classification system subdivides thecarotenoids into acyclic, monocyclic and bi-cyclic derivatives. Respective parent com-pounds of these categories are lycopene,γ-carotene and β-carotene. In former timesthe prefix “neo” was used to designate a caro-tenoid stereoisomer with at least one cis con-figuration in the double-bond chain. Nowa-days the position of a cis double bond cannormally be assigned unambiguously byspectroscopic methods. The prefix “apo” des-ignates a carotenoid that has been derivedfrom another carotenoid by loss of a struc-tural element through degradative action. Theprefix “pro” designates some poly-ciscarotenoids.


6

VITAMIN A IN NATURE

Figure 1.4. Carotenoid biosynthesis from isoprenoid units (IDP, DMAD).

Isopentenyl diphosphate (IDP)

O P P

Dimethylallyl diphosphate (DMAD)

O P P

O P P

Geranyl diphosphate (GDP)(2 x IDP)

O P P

Geranylgeranyl diphosphate (GGDP)

Dimerization

PhytoeneDehydrogenation

Lycopene(ψ, ψ-Carotene) Cyclization

β-Carotene (β, β-Carotene)


7

Chapter 1

Because carotenoids possess many con-jugated double bonds – usually 9 to 13 – eachcan form many geometric isomers. The totaltheoretically possible number of compoundsin the whole class runs into hundreds of thou-sands. Until recently attention has beenfocussed on a few dozen carotenoids that arein the all-trans configuration. The presenceof a cis double bond predisposes to increasedthermodynamic instability.

The most characteristic feature of caroten-oid structure is the long system of alternatingdouble and single bonds, the polyene chain,that forms the central part of the molecule. Itis this that gives carotenoids their distinctivemolecular shape, chemical reactivity and light-absorbing properties. Usually, the most sta-ble form of the polyene chain is a linear, ex-tended conformation, as in lycopene.

The ability of carotenoids to absorb visuallight is related to the presence of delocalizedπ-electrons. In plants energy transfer can takeplace from excited carotenoids to generateexcited chlorophyll, which is active in photo-synthesis. In leaves carrying out photosyn-thesis the physical structure of the chloroplast,the subcellular structure containing the caro-tenoid, facilitates this transfer of energy tochlorophyll (Britton, 1995).

Under conditions of high light intensity thetriplet state of chlorophyll can accumulate andcause damage. Carotenoids can counteractthis effect in two ways: by deactivating thetriplet state of chlorophyll or by converting sin-glet-state oxygen to its ground triplet state andagain allowing release of the transferred en-ergy as heat (Britton, 1995).

Because of their high degree of unsat-uration carotenoids can extract or donateelectrons, resulting in radical anions and cati-ons which can react with oxygen or other mol-ecules, showing both antioxidant andprooxidant properties under various condi-

tions. It is important to realize that these prop-erties appear to be in no way related to provi-tamin function. At the present time a great dealof research effort is being directed towardsthe potential role of carotenoids and otherantioxidant nutrients in the prevention of ma-jor chronic diseases such as cancer and coro-nary heart disease (see Chapter 10).

As a group, carotenoids are nonpolar andextremely hydrophobic with virtually nosolubility in water. They are therefore re-stricted to hydrophobic areas in cells, suchas the inner core of membranes. The for-mation of carotenoid-protein complexes innature allows them access to an aqueousmedium such as blood plasma.

The many activities of carotenoids havebeen classified into functions, actions, andassociations (Olson, 1996) and this topic isexplored on this basis in Chapter 3.

Vitamin A

Vitamin A is now considered to be a subgroupof a class of compounds known as retinoids.All retinoids are derived from a monocyclicparent compound containing five carbon-car-bon double bonds and a functional group atthe end of the acyclic portion. The termVitamin A is used generically for all β-iononederivatives (other than carotenoids) that havethe biological activity of all-trans retinol.

Both vitamin A and carotenoids are solublein most organic solvents but not in water. Likeother hydrophobic substances their transportwithin the body, which is over 60% water,poses problems which have been overcomeby a variety of means (see Chapter 3). Theirsensitivity to oxidation, isomerization, andpolymerization leads to their ready destruc-tion especially when adsorbed as a thin sur-face film in the presence of light and oxygen.This has important implications for the stor-age and analysis of biological tissues.


8

VITAMIN A IN NATURE

Methods of analysis

Analytical procedures

Vitamin A has several physical propertieswhich have been exploited in its analysis inthe past. These include a characteristic ultra-violet (UV) absorption with an absorptionmaximum of 325 nm and greenish fluores-cence at 470 nm when excited at 325 nm. Ablue chromophore, which is unfortunatelytransient, forms on exposure to certain Lewisacids, such as antimony trichloride (Carr-Pricereaction) and trifluoroacetic acid (Neeld-Pearson reaction). Carotenoids also havecharacteristic UV absorption spectra. Nowa-days vitamin A and carotenoids are most gen-erally measured by high-performance liquidchromatography (HPLC). Straight-phaseHPLC is most suitable for separating cis andtrans isomers, and reverse-phase HPLC bestseparates compounds of different polarity. Toprevent oxidation and polymerization, sam-ples should be immediately analyzed orstored frozen in the dark at -70oC (Furr, Barua,Olson, 1992).

Recently there has been increased inter-est in the use of plasma retinol-binding pro-

tein (RBP) as a surrogate for plasma retinol.This has been measured by radial immuno-diffusion (Almekinder, Manda, Kumwenda etal, 1999) and in a rapid field test using driedblood spots by fluorometry (Craft, 1999), andalso by HPLC (Craft, Haitema, Brindle et al,2000).

Bioassay procedures

Biological tests have played a very importantpart in assessing vitamin A activity. These in-clude the classical growth response tests invitamin A-deficient rats, liver storage assaysin rats and chicks, and the vaginal smear tech-nique. Cell culture systems have been intro-duced for assessing the biological activity ofretinoids (Olson, 1991).

Carotenoid analysis in foods

Broadly speaking there are two main meth-ods for estimating carotenoid content of food-stuffs – open-column method and HPLC(Rodriguez-Amaya, 1999). The open-columnmethod is simpler and much less costly andquite satisfactory for the main four or fivecarotenoids in a sample.


9

Human communities rely on a very wide rangeof plant and animal foods to meet their di-etary requirements for vitamin A. Ovo-lactovegetarians and those who eat no foods ofanimal origin (vegans) can usually obtain alltheir nutritional needs from plant sourcesalone, with the exception of vitamin B12. Ani-mal products are usually expensive and arerarely relied on almost exclusively to meetrequirements. Figure 2.1 shows the food sup-ply of vitamin A for the period 1979–81 in the

world as a whole and in 6 regions. It is notthought that the data have altered substan-tially since. It should be noted that Asia andAfrica, where the most serious problems ofVADD occur, place the greatest reliance onvegetable sources. Furthermore, inter-re-gional variations are greater for preformedvitamin A intake than for total vitamin A avail-ability. These facts should have some influ-ence on food policy as it bears upon the pre-vention of VADD.

FOOD SOURCES

Figure 2.1. Food supply of total vitamin A partitioned by the percentage available from provitamin Acarotenoids (cross-hatched segments, % indicated) and preformed vitamin A food sources (open seg-ments), for the period 1979–81 (FAO/WHO Expert Consultation, 1988).

Chapter 2


10

FOOD SOURCES

Table 2.1. Provitamin A values in toma-toes: comparison of different analyticalmethods (Simpson, Chichester, 1981)

Methodology Average valueµg/g

β-carotene by HPLC 1.218β-carotene and lycopene by HPLC 11.001AOAC* method 18.063

* Association of Official Analytical Chemists

bioconversion of carotenoids may be influ-enced by many different factors. The doubtthat has recently been cast on the efficacy ofdark green leaves and some other sourcesof provitamin A has stimulated much researchactivity in this field (see p 18).

Provitamin A carotenoidsources

Dark green leafy vegetables, yellow fruits,orange roots – mainly carrots – and the oilsof palms are the main sources of provitaminA. Among leaves only those that are darkgreen are really good sources. This is be-cause their carotenoid content in chloroplastsis roughly proportional to the concentrationof chlorophyll with which they are associatedfor photosynthesis. Edible dark green leavesare readily available in most areas whereVADD are a problem. The species vary con-siderably from place to place and Table 2.3shows just a few examples of typical provita-min A values for some that are commonlyconsumed and have proved useful in inter-vention programmes. More exhaustive listsof similar data on a national or regional basisare becoming increasingly available andsome examples are included in this Manualin Further Reading.

The data in Figure 2.1 are for provitamin Acarotenoid intake. Although similar data fornonprovitamin carotenoid intake are not avail-able, from what is known of the carotenoidcomposition of common fruits and vegetablesit is probable that the intake of nonprovitamincarotenoids is even greater than that of pro-vitamin carotenoids. The significance of thisfor human health has only been becomingevident in recent years (see Chapter 10).

Units of vitamin A activityEarlier analytical methods failed to distinguishbetween individual carotenoids and as a re-sult nonprovitamin carotenoids, were fre-quently included along with those with vita-min A activity when concentrations were re-ported in food composition tables for fruits andvegetables. For example, one analysisshowed that as little as 7% of the carotenevalue estimated was actually β-carotene orprovitamin A. The introduction of HPLC pavedthe way for the solution of this problem but ithas taken time for accurate analyses to bemade and for the results to replace the older,inaccurate values in food composition tables(see Table 2.1). It is clearly important to checkthe method of analysis before utilizing valuesfor provitamin A carotenoid activity in publi-cations.

Another problem that has to be addressedwith regard to the vitamin A activity of food-stuffs is the need to make allowances for thedifferences in activity between retinol itselfand β-carotene and also the need to differ-entiate between the activity of β-carotene andother provitamin carotenoids. The reasons forthese differences will be considered later (seep 16). The generally accepted position on therelationships between different expressionsof vitamin A activity up until the present timeis as shown in Table 2.2.

The values for provitamin activity are ap-proximations because the bioavailability and

FOOD SOURCESSIGHT AND LIFE MANUAL

11

Chapter 2

Table 2.2. International Units (IU) and Retinol Equivalents (RE)

Compound µg/IU IU/µg RE/µg µg/RE

all-trans retinola 0.300 3.33 1.000 1.0

all-trans retinyl acetate 0.344 2.91 0.873 1.15

all-trans retinyl palmitate 0.549 1.82 0.546 1.83

all-trans β-caroteneb 1.800 0.56 0.167 6.0

Mixed carotenoidsc 3.600 0.28 0.083 12.0

a: Molecular weight = 286.44; 1 µmol = 286.44 µg, 10 µg/dL = 0.35 µmol/L, 1 µg = 0.00349 µmol;60 mg = 200,000 IU = 209.5 µmol

b: Molecular weight = 536.85c: Provitamin A carotenoids other than β-carotene

Vegetables

Current analyses tend to report the contentof each carotenoid identified, irrespective ofpresence or absence of provitamin activity.This has the additional value of indicating thevalue of the foodstuff as a source of antioxi-

dant activity. Table 2.4 shows the lutein andβ-carotene concentrations in green vegeta-bles.

In leafy vegetables β-carotene and luteinare the major carotenoids and together ac-count for over 80% of all carotenoids. α- andγ-carotene, cryptoxanthin and lycopene areminor components.

Carrots are increasingly being grown inparts of the developing world and may varyconsiderably in carotenoid content (see Ta-ble 2.5). A characteristic feature is the rela-tively high concentration of α-carotene, usu-ally about half of that of β-carotene.

In tomatoes lycopene usually far exceedsthe concentration of β-carotene, althoughsome varieties rich in β-carotene have beendeveloped. Tomato and tomato products areby far the best source of lycopene, which isof considerable interest in relation to someprevalent diseases worldwide (see Chapter10).The main carotenoids in pumpkin are α-carotene, β-carotene and lutein.

Table 2.3. Examples of common vegeta-ble/fruit-carotenoid sources

µg RE/100 gedible portion

Mango (golden) 307Papaya (solo) 124Cucurbita (mature pulp) 862Buriti palm (pulp) 3,000Red palm oil 30,000Carrot 2,000Dark green leafy vegetables 685Tomato 100Apricot 250Sweet potato, red and yellow 670


12

FOOD SOURCES

Table 2.4. Lutein and β-carotene concentrations in green vegetables (µg/100 g freshweight) (Ong, Tee, 1992)

Vegetable Lutein β−Carotene

Green, leafy* (4 types) – 330–5,030

Green, nonleafy (6 types) – 217–763

“Cruciferous” vegetables (5 types) 280–34,200 80–14,600

Leafy vegetables (32 types) – 1,000–44,400

Tuberous vegetables and beans (16 types) – 40–1,700

Green, Ieafy* (7 types) 250–10,200 1,000–5,600

Other vegetables (19 types) trace–440 11–430

Green, leafy* (27 types) 73–29,900 97–13,600

Green, nonleafy (8 types) 142–460 74–569

* Values from different references

Fruits

The vitamin A activity of fruits is generallylower than that of leafy vegetables and theircarotenoid content is more complex. Theirgreater acceptability, especially to young chil-dren, is an advantage as far as interventionprogrammes are concerned (see Table 2.6).The “sweet paste” of the buriti (Mauritiavinifera) fruit in north and central Brazil is al-most as rich in provitamin A carotenoids as isred palm oil (see below).

Roots and tubers

Fewer analyses have been carried out onroots and tubers than on vegetables or fruitsand most of the varieties examined have hadlow contents (see Table 2.7). However, thehigher values for some pigmented varietiessuggest that plant breeding for these mightbe of importance.

Vegetable oils

Carotenoids are present in most oils that areconsumed but usually in low concentration.Red palm oil (Elaeis sp. see Table 2.8) con-tains the highest carotenoid concentration inthe vegetable kingdom and has been exten-sively studied, for its unsaturated fatty acidcontent as much as for its high β-carotenecontent. It is also a rich source of other di-etary substances such as vitamin E,ubiquinones and phytosterols. Different spe-cies have different concentrations (see Table2.8) as do different oil extracts (see Table 2.9).It is the main cooking oil in most regions ofwest and central Africa, but the tree is alsocultivated in parts of Asia and of SouthAmerica. Red palm oil used in cooking im-parts a distinctive taste to food that may notbe readily accepted by some people. Highlyrefined red palm oil is increasingly being madeavailable and is much more readily accept-


13

Chapter 2

able than the crude form. Many authoritiessee a major role for this oil in the control ofVADD in the future (Kritchevsky, 2000;Nagendran, Unnithan, Choo et al, 2000; andRao, 2000), see Chapter 11.

Other sources

Hen’s eggs are often considered to be a richsource of provitamin A because of the richcolour, but the major pigments are lutein andzeaxanthin, and β-carotene makes up lessthan 7% of the total. Some fish flesh is brightlycoloured, but most of the pigment arexanthophylls.

Table 2.5. α- and β-carotene concentrations in carrots (µg/100 gfresh weight) (Ong, Tee, 1992)

Carrot α-Carotene β-Carotene

Raw 2,000–5,000 4,600–12,500Canned 3,200–4,800 7,000–11,000Frozen 8,400–8,800 26,000–28,100

Raw 3,790 7,600

Raw, A+ hybrid 10,650 18,350Freshly cooked, A+ hybrid 15,000 25,650Canned 2,800 4,760

Line B6273 Lyophilized 3,400 6,000 Raw 3,200 5,200 Frozen 3,100 5,100

Line B9692 Lyophilized 6,100 13,800 Raw 6,600 11,700 Frozen 6,600 11,600

HCM line Lyophilized 20,300 28,200 Raw 20,600 25,100 Frozen 20,400 25,500

Raw 19 cultivars 2,200–4,900 4,600–10,300

Raw 3,410 6,770


14

FOOD SOURCES

Table 2.6. Carotenoid concentrations in fruits (µg/100 g fresh weight) (Ong, Tee, 1992)

Fruit Lutein Cryptoxanthin Lycopene α-Carotene β-Carotene

Banana 20–40 0 0 60–160 40–100

Berries, grapes,

black currant 20–200 0 0 0–60 6–150

Mango – – – – 63–615

Orange, mandarin 20–30 7–300 – 20 25–80

Papaya, watermelon 0 450–1,500 2,000–5,300 0 228–324

Starfruit 60 1,070 0 0 28

Natural extracts containing carotenoidshave long been used for colouring foods tomake them appear more attractive. Thesehave included extracts from leaves, carrotsand red palm oil. β-carotene was the first syn-

thetic carotenoid to be used as a food colourand others are β-apo-8'-carotenal andcanthaxanthin. The former two have vitaminA activity and therefore they also contributeto nutrient intake.

Table 2.7. Carotenoid concentrations in selected roots and tubers (µg/100 g fresh weight)(Ong, Tee, 1992)

Root or tuber Lutein Cryptoxanthin Lycopene β−Carotene

Sweet potato

Different varieties – 0 – 5–551

– – – 1–4

Yellow variety 25 0 42 19

Orange variety 7 27 147 1,140

Cassava

White variety 2 3 1 20

Yellowish – – – 40–790

Potato 13–60 Trace Trace 3–40

Taro 3–31 1 1–3 2–16


15

Chapter 2

Bioavailability of carotenoidsOf all the sections in this book this one hasprobably undergone the most significant de-velopments since the 1st edition was writtenin 1996–97. The advances that are takingplace in our understanding of the bio-availability of provitamin A carotenoids is hav-ing a profound impact on the approaches thatare being adopted to the control of VADD (seeChapter 11).

Although it is all too easy to pass judge-ment with the benefit of hindsight it does nev-ertheless seem quite astounding that deci-sions that were taken on little or no evidencein the mid 1960s were allowed to remain un-challenged and have formed the basis for ac-tion for the subsequent 30 years and more.The Joint FAO/WHO Expert Group (1976) in-

troduced the term Retinol Equivalent and as-signed β-carotene 1/6 and other provitamin Acarotenoids 1/12 the value of preformed vita-min A on the very scanty evidence availableat that time (Hume, Krebs, 1949). The con-cept has proved to be of immense help inassessing the equivalence of differentsources of vitamin A activity. The actual val-ues remained untested, despite a strong callfrom the committee for research, and led to afalse sense of security until challenged in themid 1990s.

In fairness it should be recalled that in the1960s and long thereafter attention in this fieldwas focussed on xerophthalmia and its pre-vention. Intermittent large-dose supplemen-tation was the prevailing control measure forthis emergency situation. The growing andconsumption of dark green leafy vegetables(DGLV) was encouraged as a long-term so-lution, but it received little attention at inter-national meetings. Most sources of food com-position data at this time did not distinguishbetween provitamin and non-provitamincarotenoids.

In the mid 1980s evidence began to accu-mulate that widespread subclinical vitaminA deficiency could lead to a significant in-crease in the risk of mortality and morbidityin young children. It began to become clearthat while consumption of dark green leavesand yellow fruits could protect against se-vere VAD leading to xerophthalmia it mightnot be capable of preventing subclinical vi-tamin A deficiency in a substantial propor-tion of the young child population of devel-oping countries.

The group at the Department of HumanNutrition at Wageningen, Netherlands, hasbeen at the forefront of the new investigationsinto the bioavailability of dietary carotenoids,nonprovitamin A as well as provitamin A. Theyhave also led in the study of the many andcomplex factors that determine bioavailability.

Table 2.8. Total carotenoids (ppm, esti-mated at 446 nm) from various oil palmspecies (Ong, Tee, 1992)

E.o. 4,347E.o. x E.g. (D) 1,846E.o. x E.g. (P) 1,289E.o. x E.g. (D) x E.g. (P) 864E.g. (P) 380E.g. (D) 948E.g. (T) 610

E.o., Elaeis oleifera; E.g., Elaeis guineensis;D, Dura; P, Pisifera; T, Tenera

Table 2.9. Carotenoid contents of palm oilextracts (ppm) (Ong, Tee, 1992)

Crude palm oil 630–700Crude palm olein 680–760Crude palm stearin 380–540Second pressed oil 1,800–2,400Residual oil from fibre 4,000–6,000


16

FOOD SOURCES

de Pee, West, Muhilal et al (1995) in In-donesia found that an additional daily por-tion of dark green leafy vegetables given tolactating women did not improve vitamin Astatus (as measured by serum retinol,breast milk retinol, and serum β-carotene).In those who received a similar amount ofβ-carotene on a wafer there was significantimprovement. A review of previous studies(de Pee, West, 1996) found many of thosewith positive results had design faults andmore recent, better controlled studiestended to be negative. Later work showedthat in central Java vegetables played alesser part in maintaining vitamin A statusthan had been thought (de Pee, Bloem,Gorstein et al, 1998) and orange fruits weremore effective in improving vitamin A sta-tus than dark green leafy vegetables (dePee, West, Permaesih et al, 1998). Thecalculated β-carotene : retinol equivalencein leafy vegetables and carrots was 26:1(compare below). A study in Guatemala,where 50 g of cooked carrots were addedto the diet of children aged 7–12 years failedto find evidence of nutritional benefit (Bulux,Quan de Serrano, Giuliano et al, 1994). Astudy in Ghana (Takyi, 1999) found that con-sumption of DGLV with added fat signifi-cantly increased serum retinol levels in chil-dren, but even so just over 50% remainedwith inadequate vitamin A status.

On the other hand, more recently (Tang,Gu, Hu et al, 1999) in China the effect on vi-tamin A body stores of children 3–7 years oldof two vegetable diets was studied by a dou-ble stable isotope method. Vitamin A labelledwith two different kinds of deuterium (D4 andD8) was administered before and after theintervention to estimate changes in total bodyvitamin A stores that occurred. One group re-ceived their daily customary intake of 56 g ofgreen-yellow vegetables and 224 g of light-coloured vegetables, and the other received238 g of green-yellow vegetables and 34 g oflight-coloured vegetables. Only the latter diet

maintained adequate vitamin A stores. It wascalculated from the isotope studies that pro-vitamin A carotenoids (mainly β-carotene) pro-vided an estimated vitamin A equivalence of27:1 on average (see above). It should benoted that to achieve this effect more than1/4 kg of vegetables was consumed each dayby these young children, as young as 3 years.Another study of the bioavailability of β-caro-tene from oriental vegetables found higherbioavailabilities, but still much less than frompurified β-carotene beadlets (Huang, Tang,Chen et al, 2000).

Factors affecting bioavailability

The Wageningen group has introduced amnemonic (SLAMENGHI) to assit in the dis-cussion of this complicated subject (Table2.10) (see also Further Reading). It shouldbe pointed out that the question of bio-availability applies not only to provitamin Acarotenoids, but also to nonprovitamin Acarotenoids, such as lycopene, lutein and oth-ers whose possible role in prevention or treat-ment of a number of diseases is discussed inChapter 10.

Before something is said on each of theseaspects the use of another term may be men-tioned. Bioconversion is not the same asbioavailability, it relates to the efficiency withwhich the carotenoid in question is convertedto vitamin A in the body. There is little infor-mation on this subject. The 1976 FAO/WHOExpert Group assumed that β-carotene hastwice the efficiency of other provitamin Acarotenoids.

“S”pecies of carotenoids

The naturally occurring configuration ofcarotenoids in plants is usually the all-transisomer. It is more readily absorbed in manthan the 9-cis form. A significant proportionof 9-cis β-carotene is converted to the all-transform before entering the blood stream.


17

Chapter 2

Molecular “L”inkage

Esters of carotenoids are common in fruit andvegetables but their absorption has beenstudied little. Esters of lutein are reported tobe more bioavailable.

“A”mount of carotenoids consumedin a meal

In a meta-analysis that included 31 studies inwhich a daily β-carotene supplement of<50 mg lasted <1 year it was found that theduration of β-carotene supplementation wasa significant predictor of β-carotene response(Castenmiller, West, 1998).

“M”atrix in which the carotenoid isincorporated

In green leaves carotenoids exist withinchloroplasts as pigment-protein complexeswhich require disruption of the cells for thecarotenoid to be released. In other vegeta-bles and fruits carotenoids are sometimesfound in lipid droplets from which they maybe readily released. Cooking assists in therelease, but if excessive may lead to oxidativedestruction of the carotenoid. The carbon-carbon double bonds of carotenoids are sub-ject to oxidation by oxygen in the air, and heatmay bring about structural changes includ-ing isomerization of all-trans carotenoids tocis forms.

Table 2.10. Effect of food matrix and processing on bioavailabilityof carotenoids (after Boileau, Moore, Erdman Jr, 1999)

Very high bioavailability

Formulated natural or Formulated carotenoids insynthetic carotenoids water-dispersible beadlets

Natural or synthetic Carotenoids – oil form

Papaya, peach, melon Fruits

Squash, yam, sweet potato Tubers

Tomato juice Processed juice with fat-containing meal

Carrots, peppers Mildly cooked yellow/orange vegetables

Tomato Raw juice without fat

Carrots, peppers Raw yellow/orange vegetables

Spinach Raw green leafy vegetables

Very low bioavailability (<10%)


18

FOOD SOURCES

“E”ffectors of absorption andbioconversion

Dietary components may influence absorp-tion. A minimum of 5 g fat daily is required foradequate micelle formation. This appears tobe sufficient for optimal absorption of α-caro-tene, β-carotene and vitamin E, but luteinesters require more (Roodenburg, Leenen,van het Hof et al, 2000). Adequate proteinand zinc intake assists maintenance of vita-min A status. Vitamin E, as an antioxidant,protects vitamin A from being oxidized. Fibre,chlorophyll and nonprovitamin carotenoids,which are commonly present in the diet, tendto reduce bioavailability. There is evidencethat alcohol ingestion interferes with the con-version of β-carotene to vitamin A.

“N”utrient status of the host

Absorption of carotenoids is influenced by vi-tamin A status. If it is low, conversion ofcarotenoids to vitamin A is likely to be in-creased. There is evidence that zinc defi-ciency impairs the efficiency of β-caroteneconversion to vitamin A.

“G”enetic factors

As clinical genetics advances it is likely thatfurther cases of rare gentic defects as thecause of vitamin A deficiency will be reported.To date three types of defect are known:enzymatic failure to cleave β-carotene in thesmall intestinal mucosa (McLaren, Zekian,1971), heterozygotic reduction of plasma RBP(Matsuo, Matsuo, Shiraga et al, 1988), andmutations in the gene for retinol-binding pro-tein (Biesalski, Frank, Beck et al, 1999) (seealso Chapter 10).

“H”ost-related factors

The serum response to β-carotene is higherin women than in men but the reason is notknown. In several ways men are more

susceptible to develop VAD than women. Agedoes not appear to be a factor. Diseases thatinterfere with intestinal absorption, especiallyof lipids, are likely to impair carotenoidbioconversion. In terms of public health, es-pecially in developing countries, intestinalparasites such as Ascaris lumbricoides andGiardia lamblia are of great importance (seeChapter 9).

Mathematical “i”nteractions

This final letter of the mnemonic refers to thepossible synergistic or even antagonistic ef-fect that two or more factors might have whenacting together. At present this is a theoreti-cal concept only, as data are lacking, but itwill have to be borne in mind as knowledgeprogresses.

Remarks

As might be expected, better results from in-terventions tend to occur when more than oneadverse factor is counteracted. For example,increased fat intake and anthelminthic drugtreatment have enhanced the effectivenessof food-based programmes (Jalal, Nesheim,Agus et al, 1998).

The methodology for the accurate determi-nation of provitamin A carotenoid bioactivityin man is still in an early and rapidly growingstage of its development. There are two mainapproaches; techniques that rely on changesin one or more indicators of vitamin A status,and those that provide a more direct estimateof absorption and/or conversion efficiency ofsingle doses of provitamin A carotenoids(Parker, 2000). It seems unlikely that precisevalues will be set, as in the past, but it shouldbe possible eventually to provide reliable,practial information for application in interven-tions for the control of VADD. There is evi-dently a great deal more painstaking researchthat needs to be done (Traber, 2000). Mean-while, efforts to promote the consumption of


19

Chapter 2

green leaves and yellow fruits remain a ma-jor element of control programmes.

Preformed vitamin AMention has already been made of fish liveroils as highly concentrated sources of vita-min A. They are used as pharmaceuticalsrather than as items of diet. Fish liver is oftendiscarded along with other soft organs, but if

Table 2.11. Examples of common animalvitamin A sources (µg retinol/100 g edibleportion)

Fatty fish liver oils Halibut 900,000 Cod 18,000 Shark 180,000 Herring and mackerel 50

Dairy produce Butter 830 Margarine, vitaminized 900 Eggs 140 Milk 40 Cheese, fatty type 320

Meats Liver of sheep and ox 15,000 Beef, mutton, pork 0–4

utilized could form a valuable source of thevitamin in many parts of the developing world.The storage form is vitamin A1 alcohol (reti-nol) in salt water fish. In fresh water fish it isvitamin A2 alcohol (3-dehydroretinol), whichhas about 40% of the activity of retinol. Be-cause of the teratogenic effects of large dosesof vitamin A the consumption of liver is con-traindicated during pregnancy (Ministry ofAgriculture, Fisheries and Food, UK, 1995).Most mammalian livers consumed, such asthose of calves, ox, lambs or chicken, haveconcentrations that are comparable to thosein cod liver oil. Milk, butter, cheese and eggsare all moderate sources. Table 2.11 gives aselection of preformed vitamin A concentra-tions of some common foods.

Vitamin A has been added successfully tomany foods (Bauernfeind, 1981). What istermed food fortification (or occasionally nutri-fication) is one of the major long-term ap-proaches to the control of the problem ofVADD and is discussed further in Chapter 11.


21

In recent years knowledge of the physiology,biochemistry and molecular biology of vita-min A has advanced enormously. More isprobably known than for any other vitamin inman.

Digestion and absorptionDietary preformed vitamin A and carotenoidsare released from protein in the stomach byproteolysis. They then aggregate with lipids

and pass into the upper part of the small in-testine. Dietary fat and protein and their hy-drolytic products stimulate, through the se-cretion of the hormone cholecystokinin, thesecretion of bile. This emulsifies lipids andpromotes the formation of micelles whichhave lipophilic groups on their inside and hy-drophilic groups on their outside. In this waythe absorption of fat is facilitated. Bile saltsstimulate pancreatic lipase and otheresterases that hydrolyze retinyl esters in in-

VITAMIN A IN HEALTH

Figure 3.1. Formation of retinoids from β-carotene via the proposed central (solid line) and excentriccleavage (dashed lines) pathways (Stahl, Sies, Sundquist, 1994).

Chapter 3


22

VITAMIN A IN HEALTH

testinal mucosal cells (enterocytes). Retinol,the product of the hydrolysis, is well absorbed(70–90%) by intestinal mucosal cells.

Provitamin A carotenoids pass into themucosal cells unchanged. A proportion ofeach, along with non-provitamin carotenoids,passes through unchanged into the lymphand the blood. The remainder undergoescleavage of the molecule by a specific en-zyme 15,15'-dioxygenase within the intesti-nal mucosal cell. This process can also takeplace within the liver and some other tissues(Goodman, Huang, Shiratori, 1966). Sym-

Fig 3.2. Absorption of preformed vitamin A and provitamin A from the small intestine. RE, retinyl ester;ROH, retinol; CM, chylomicron (Blomhoff, 1994).

metrical cleavage of the β-carotene moleculeyields two molecules of retinal, which is mostlyreduced and esterified to retinyl ester. Somecleavage is asymmetrical and less retinal isproduced (see Figure 3.1). In practice β-caro-tene and other provitamin A carotenoids haveonly a fraction of the activity of retinol, as waspointed out earlier (see Tables 1.1 and 2.2).

Within the mucosal cells retinol is esteri-fied before incorporation into chylomicrons(see Figure 3.2). In this process a specificcellular retinol-binding protein (CRBPII) car-ries the lipid-soluble retinol through the aque-

VITAMIN A IN HEALTHSIGHT AND LIFE MANUAL

23

Chapter 3

ous media and delivers it to the enzymelecithin:retinol acyltransferase (LRAT) (Ong,Kakkad, MacDonald, 1987). This enzymeappears to be the main intestinal enzyme thatnormally esterifies retinol and then delivers itto the chylomicrons.

In terms of intake of vitamin A in the diet,about 10% is not absorbed, 20% appears inthe faeces through the bile, 17% is excretedin the urine, 3% is released as CO2 and 50%is stored in the liver (Olson, 1994).

Transport to the liverChylomicrons consist of aggregates of thou-sands of molecules of triglycerides andphospholipids with fat-soluble vitamins, in-cluding retinyl esters and carotenoids, cho-lesterol esters and some apolipoproteins (seeFigure 3.3).

Figure 3.3. Schematic drawing of chylomicron and chylomicron remnant (Blomhoff, 1994).

They pass into the lymph and then the gen-eral circulation and are broken down to someextent to produce chylomicron remnants. Al-most all retinyl esters remain with the chy-lomicron remnants, which are mainly clearedby the liver. Recent work has demonstratedthat they also deliver retinyl esters to lung andsome other tissues, and also to some cancercells (Blomhoff, 1994). In these sites they areconverted to retinoic acid, which can be usedfor regulation of gene expression (see later).

Metabolism in the liverIn the liver (see Figure 3.4) most vitamin Afrom chylomicron remnants in the form ofretinyl esters is taken up by hepaticparenchymal cells (hepatocytes). There theesters are hydrolyzed and after processingin endosomes retinol is transferred to the en-doplasmic reticulum. There it binds to retinol-


24

VITAMIN A IN HEALTH

binding protein (RBP) and after the complexenters the Golgi complex it is secreted fromthe cell.

In the absence of retinol RBP is retainedby the liver and tends to accumulate (Rask,Valtersson, Arundi et al, 1983). This ill-under-stood phenomenon forms the basis of rela-tive dose-response tests (RDR) of vitamin Astatus (see Chapter 4).

Most of the retinyl ester taken up byhepatocytes from chylomicron remnants istransferred as retinol attached to RBP toanother type of liver cell called stellate cells

Figure 3.4. Schematic diagram of the liver structure (Blomhoff, 1994).

(Wake, 1994). Storage of vitamin A as retinylesters seems to be one of the main functionsof this type of liver cell. They also producecollagen type III, which when excessive maycontribute to a form of cirrhosis of the liver(see also Chapter 10). 50–80% of vitamin Ain the body is in the liver. 90–95% of this is inthe stellate cells and 98% of this is in the formof retinyl esters, mostly as palmitate. Thisstore is normally sufficient to last for severalmonths. Bound to RBP retinol is released fromboth stellate and parenchymal cells. Whenliver reserves of vitamin A are lowparenchymal cells are the major site of stor-age (Batres, Olson 1987). Some parenchymal


25

Chapter 3

cells contain much more vitamin A than oth-ers. These are respectively termed “heavy”or “light” according to their density (Batres,Olson, 1987a).

Cells identical to the liver stellate cells alsooccur in many other tissues of the body, in-cluding the lung, intestine and kidney (Nagy,Holven, Roos et al, 1997). Recently it hasbeen shown that adipose tissue is an impor-tant storage site for retinol, as well as forβ-carotene (Wei, Lai, Patel et al, 1997). About15–20% of the rat’s store of retinol is inadipocytes. This comes from chylomicron-bound esters and not from circulating RBPas is the case of that in the liver. Furthermore,free retinol is secreted rather than retinolbound to RBP. The secretion of vitamin A from

the liver is a complicated process and bytracer kinetics in animal studies several poolshave been identified (Green, Green, 1996).

Transport to other cellsRetinol in plasma bound to RBP is almostentirely associated also with another protein,transthyretin (TTR) (Ingenbleek, Young,1994). The formation of this complex reducesthe loss of retinol in glomerular filtrate in thekidney. RBP has been fully characterized andis a single polypeptide chain with a molecu-lar weight of 21,230. Its three-dimensionalstructure is such that it contains a special-ized hydrophobic pocket within which the fat-soluble retinol fits (Sivaprasadarao, Findlay,1994).

Table 3.1. Properties and functions of some selected lipocalins (after Sivaprasadarao,Findlay, 1994)

Protein Size* Tissue Fluid Ligand Property/Function

β-Lactoglobulin 2 x 162 Mammary Milk Retinol (?) Possible involvementgland in transport of

vitamin A via gutreceptor

Serum retinol- 183 Liver and Serum Retinol, retinal, Retinol transport,binding protein other retinoic acid delivery of retinol(RBP) tissues to tissues via a

receptor

Complement 182 Liver Serum Retinol, Component ofC8γ retinoic acid complement

Apolipo- 169 Adrenal, Serum, Lecithin, Lipid transport,protein D kidney, gut cholesterol enhances lecithin:(ALPD) pancreas, secretion cholesterol acyl-

liver transferase activity

* Number of residues


26

VITAMIN A IN HEALTH

In well-nourished adults total RBP concen-tration in plasma is 1.9–2.4 µmol/l (40–50 µg/ml). The value for children is about 60% ofthat of adults. Protein-energy malnutrition,infections and parasitic infestations lower con-centrations of RBP in plasma and these mustbe used with caution in assessing vitamin Astatus (see Chapter 4).

RBP is a member of a family of proteins,the knowledge of which is rapidly growing. Itincludes proteins that bind to other lipid-solu-ble molecules. This group of proteins is calledthe lipocalin superfamily. Table 3.1 showssome of these.

RBP is synthesized in hepatocytes, butprobably also in many other tissues.

In healthy subjects mean values and rangesof serum retinol as a function of age and sexare shown in Table 3.2. In most age ranges,levels are higher in males.

Retinol is extensively recycled betweenplasma, liver and other tissues. At present itis thought that most of the irreversible utiliza-tion of retinol is a kind of detoxification, andonly a small fraction is functional. Smallamounts of other retinoids can be detectedin plasma, including all-trans retinoic acid.

There is a variety of molecules for the ex-tracellular transport of retinoids andcarotenoids (see Table 3.3). It will be notedthat there are no specific carrier proteins forcarotenoids.

Concentrations of carotenoids in plasma(see Figure 3.5) are highly dependent on diet.In the case of provitamin A carotenoids usuallevels in plasma are significantly higher inwomen than in men (Olmedilla, Granado,Blanco et al, 1994), in contrast to retinol.

Table 3.2. Serum retinol concentrations (µmol/L) as a function of age and sex in Ameri-can residents, 1971–74* (Olson, 1996)

Age (years) Total Males Females

3–5 1.28 (0.73–2.0) 1.29 (0.70–2.1) 1.26 (0.77–2.0)n 1414 725 689

6–11 1.31 (0.84–1.9) 1.30 (0.84–1.9) 1.32 (0.84–1.9)n 1857 930 927

12–17 1.58 (1.0–2.3) 1.62 (1.1–2.3) 1.53 (1.0–2.2)n 2035 1026 1009

18–44 1.94 (1.2–2.9) 2.08 (1.4–3.0) 1.80 (1.1–2.8)n 7035 2164 4871

45–74 2.20 (1.3–3.3) 2.29 (1.4–3.5) 2.11 (1.3–3.2)n 6111 2911 3200

* The 5th and 95th percentile values are given in parentheses. Derived from Pilch, 1987


27

Chapter 3

Figure 3.5. Pie diagram of a typical carotenoid pattern in plasma.

Table 3.3. Extracellular transport molecules for retinoids and carotenoids (Blomhoff, 1994)

ApproximateMW (kD) Main ligand Suggested function

Chylomicrons 20,000–200,000 Retinyl esters Lymph and plasma transportand their remnants and carotenoids of newly absorbed vitamin A

and carotenoids

VLDL and LDL 2,000–20,000 Carotenoids Plasma transport of carotenoids

RBP 21 Retinol Blood plasma and interstitial fluidtransport

IRBP 140 Retinol, retinal Intercellular transportin visual cycle

EBP 20 Retinoic acid Intercellular transportin epididymis

VLDL, very low-density lipoproteins; LDL, low-density lipoproteins; RBP, retinol-binding protein; IRBP,interphotoreceptor retinol-binding protein; EBP, epididymal-binding protein


28

VITAMIN A IN HEALTH

Cellular uptakeSome retinol may enter cells by diffusion butthe evidence is that most is taken up by mem-brane RBP receptors which are being char-acterized at the present time (see Figure 3.6and Table 3.4). Carotenoids are mainly car-ried in plasma by low-density lipoproteins(LDLs) and enter cells bearing the LDLreceptor.

Cellular retinoid-bindingproteins (Li, Norris, 1996)

Within cells there are many proteins that spe-cifically bind retinoids and direct them to spe-cific enzymes (see Table 3.4). These proteins,like RBP, also belong to a family with other

Figure 3.6. Hypothesis for cellular RBP metabolism. RBP-retinol may be recognized by a cell surfacereceptor. Retinol may be transferred to CRBPs either at the cell surface or after internalization intoendosomes. CRBP may also deliver normal retinol to newly synthesized RBP in the endoplasmic re-ticulum (Blomhoff, 1994).

members. In recent years mounting evidencehas established key functions for CRBP inretinoid metabolism. It acts as a kind of chap-erone in protecting retinol within the cell andinteracts with certain retinoid-metabolizingenzymes (Napoli, 2000).

Gene function and retinoidsIt is known that the functions of vitamin A indifferent tissues, with the exception of thevisual process (see p 30), are mediated byits acid derivatives (Pfahl, Chytil, 1996). All-trans retinoic acid (RA) is noncovalentlybound to three nuclear RA receptors (RARa,RARb, RARg, ) in gene transcription regula-tion. When activated the nuclear receptors forvitamin A are able to bind to “response ele-ments” in specific genes to increase or de-


29

Chapter 3

crease the level of expression of the gene.The response elements are nucleotide se-quences which in the DNA compose the genes.

Soon afterwards it was shown that 9-cis RAbinds and activates three other nuclearreceptors (RXRa, RXRb, RXRg). RA onlybinds RAR receptors, whereas 9-cis RA canbind all six nuclear receptors but in vivo it ismainly bound to RXRs. Considerable surpriseresulted when the discovery was announcedof a new metabolite of retinol, all-trans-oxo-retinol, with the functions of receptor activa-tor and differentiation agent (Achkar, Derguini,Blumberg et al, 1996). It binds and trans-activates RARs but not RXRs.

The expression of these six receptors var-ies between cells, but most if not all cells ex-press at least one of these receptors. Sev-eral hundred genes have so far been shownto be induced or repressed by retinoids. Ta-ble 3.5 gives a representative listing of vita-

min A-responsive genes thought to be acti-vated through the action of RARs and/orRXRs.

These retinoid hormone receptors are nowrecognised to be part of a hormone receptorsuperfamily whose members interact. It hasbeen called the “Steroid-Thyroid-RetinoidSuperfamily”. Table 3.6 gives a partial listingof these nuclear receptors and their respec-tive activating substances. If these nuclearreceptors are to recognise response elementswithin responsive genes they must act in pairs(dimers). A member of the RXR family mustserve as a partner if the dimer is to function.It is therefore evident that vitamin A, usuallyin the form of RA, and the RXRs can beregarded as regulators of several hormoneresponse systems.

Major sources of RA in the diet are its pre-cursors retinol and retinyl esters. The diets ofanimals and man contain little RA itself. How-

Table 3.4. Intracellular retinoid-binding proteins (Blomhoff, 1994)

ApproximateMW (kD) Main ligand Suggested function

CRBP(I) 16 Retinol Donor for LRAT reaction and oxidative enzymes; regulates retinyl ester hydrolysis

CRBP(II) 16 Retinol Donor for LRAT reaction

CRABP(I) 16 Retinoic acid Regulates free retinoic acid concentration; donor for catabolizing enzymes

CRABP(II) 15 Retinoic acid Regulates free retinoic acid concentration; donor for catabolizing enzymes

CRALBP 36 Retinal Enzymatic reactions in the visual cycle

CRBP, cellular retinol-binding protein; CRABP, cellular retinoic acid-binding protein; CRALBP, cellularretinal-binding protein; LRAT, lecithin:retinol acyl transferase


30

VITAMIN A IN HEALTH

ever, it has been shown that both rat and hu-man intestinal cytosol can produce RA fromβ-carotene (Napoli, 1994). This suggests anew source for the generation of RA withinthe body.

Cytochrome P450 (CYP) enzymes consti-tute a large superfamily with hundreds ofmembers. They catalyze the oxidative me-tabolism of many endogenous compounds aswell as numerous foreign chemicals. It hasbeen proposed that P450s regulate steady-state levels of ligands for the nuclear hormonereceptor superfamily which includes retinoids(Sonneveld, van der Saag, 1998). RA is me-tabolized through oxidation to more polarmetabolites. Recently a novel cytochromeP450 enzyme (CYP26) with specific RA4-hydroxylase activity has been cloned fromman and some animal species. It fulfils all therequirements of an enzyme which could con-trol levels of active retinoids in cells and tar-get tissues. CYP26 may play a role in embry-onic development (see below and Chapter 10)and in cancer (see Chapter 10). The great

advances made in the understanding of thehormonal control retinoids exert over genefunction have highly significant implicationsfor the management and treatment of manydiseases that occur throughout the world (seeChapter 10).

Functions of vitamin AIn recent years knowledge of the functions ofvitamin A has increased greatly. Table 3.7 in-dicates the major functions of vitamin A asfar as man is concerned. In view of the factthat nuclear receptors for retinoids have beenidentified in virtually every type of cell it couldbe argued that in some way vitamin A playsa part in every bodily process. For our presentpurposes those included in Table 3.7 may beconcentrated upon.

Vision

In the outer segment of rod cells in the retina11-cis retinal combines with the membrane-bound protein, opsin, to form rhodopsin, in-

Table 3.5. Partial and representative listing of vitamin A-responsive genes thought to be regulated through the ac-tion of RARs and/or RXRs, (Blaner, 1998).

Gene Gene function/role

Oxytocin ReproductionGrowth hormone GrowthPhosphoenol pyruvate GluconeogenesiscarboxykinaseClass I alcohol dehydrogenase Alcohol oxidationTransglutaminase Cell growth and cell deathLaminin B1 Cellular interactionsMatrix Gla Protein Bone growth and strengthKeratin SkinCellular retinol-binding protein type I Vitamin A metabolismRAR-beta Vitamin A actionHox 1.6 Fetal developmentDopamine D2 receptor Central nervous system


31

Chapter 3

volved in vision under conditions of low illu-mination. Similar complexes occur in conecells to give three specific iodopsins with dif-ferent absorption maxima, resulting in blue,green and red cones. These serve colour vi-sion and vision in bright illumination. Whenlight strikes the retina a series of complex bio-chemical changes takes place, resulting in thegeneration of a nerve impulse (Rando, 1994)(Figure 3.7).

Vitamin A, in the form of all-trans retinol isdelivered by the blood to the retinal pigmentepithelium (RPE) where it is either esterifiedfor storage, or isomerized to 11-cis retinolwhich is then oxidised to 11-cis retinal. Thisis transported to the photoreceptor rod or conecells where it combines with the protein opsinto form rhodopsin or iodopsin, respectively,which are light sensitive. On exposure to light11-cis retinal is isomerized back to all-transretinal and the nerve impulse is generated. Onrelease from the protein all-trans retinal is re-duced to all-trans retinol and is transportedback to the RPE to complete the cycle.

PicsManSEd

Table 3.6. Partial listing of members of the “ Steroid-Thy-roid-Retinoid Superfamily” of nuclear receptors and theiractivators (Blaner, 1998).

Nuclear receptor Activating substance

Retinoid X receptor (RXR) 9-cis retinoic acidRetinoic acid receptor (RAR) all-trans retinoic acidVitamin D receptor (VDR) 1,25-dihydroxy vitamin DThyroid hormone (TR) Triiodo-thyronine (T3)Estrogen receptor (ER) EstrogenProgesterone receptor (PR) ProgesteroneGlucocorticoid receptor (GR) CortisolMineralocorticoid receptor (MR) AldosteroneAndrogen receptor (AR) TestosteroneLipid X receptor (LXR) Cholesterol metabolite(s)Peroxisome proliferator- Putative fatty acidactivated receptor (PPAR) metabolite

Table 3.7. An outline of functions ofvitamin A

Vision Photopic andcolour, scotopic

Cellular Genedifferentiation, transcriptionmorphogenesis

Immune response Non-specific,cell-mediated

Haemopoiesis Iron metabolism (?)

Growth Skeletal

Fertility Male and female

The space between the RPE and the layerof photoreceptor cells is taken up mostly bya large glycoprotein called the interphotore-ceptor retinoid-binding protein (IRBP) thefunction of which is to transport two differentmolecular species of vitamin A to and fromtwo different cell types, as outlined above.Chen and Noy (1994) have proposed mecha-


32

VITAMIN A IN HEALTH

nisms to account for this process. Anotherretinoid-binding protein is also unique to theeye. It is cellular retinaldehyde (retinal)-bind-ing protein (CRALBP). It binds closely to11-cis retinal and to 11-cis retinol and pro-tects the former from photoisomerization.

In the developing embryo RA is highly con-centrated in certain tissues (Dräger, Wagner,McCaffery, 1998). These patterns are gener-ated by the local expression of RA-synthe-sizing aldehyde dehydrogenase enzymes.The eye, especially vulnerable to vitamin Adeficiency, is one of the RA-richest regions inthe embryo. In the mature eye the pattern ofthese enzymes is stable, but the amount ofRA synthesized is variable and is dependenton ambient light levels. This results fromchanging levels of the RA precursor retinal,which is released from illuminated rhodopsin.Thus this is a mechanism whereby light candirectly influence gene expression. This phe-nomenon of light-induced release of retinalfrom rhodopsin occurs only in vertebrate, butnot in invertebrate, photoreceptors. It might

be speculated that this may have acceleratedthe rapid evolution of RA-mediated transcrip-tional regulation, at the transition from inver-tebrates to vertebrates. It may also explainthe prominent role of RA in the eye. Readersinterested in more detail should consult thereferences in Further Reading.

Cellular differentiation

In vitamin A deficiency keratin-producing cellsreplace mucus-secreting cells in many epi-thelial tissues of the body. This is the basis ofthe pathological process termed xerosis thatleads to the drying of the conjunctiva andcornea of the eye (see Chapter 5). The proc-ess can be reversed by vitamin A. It has be-come clear recently that vitamin A, mainly inthe form of RA, plays a key, hormone-like,role in cell differentiation throughout the tis-sues and organs of the body (Figure 3.8). Itfollows from this that the formation of RA mustbe precisely regulated. The enzymatic sys-tems responsible are under investigation(Wolf, 1996).

Figure 3.7. Current model of the visual cycle (Rando, 1994).


33

Chapter 3

Embryogenesis

Severe vitamin A deficiency on the one hand,and excessive dosing with vitamin A and alsoRA on the other, result in malformations ofthe embryo affecting most organs of the bodyin many vertebrate species. The embryo isonly sensitive to teratogenic influences, thatis to say those that induce congenital malfor-mations, during a relatively short period afterconception. After that period, known as theorganogentic period, has passed, usually thefirst three months of fetal life in man, there is

Glycoprotein andglycosaminoglycan synthesis

Glycoproteins are polypeptides with shortchains of carbohydrates. Glycosamino-glycans are related compounds that are cellsurface molecules. Retinoids have beenshown to control the expression of enzymesinvolved in the synthesis of some of thesecompounds (Vahlquist, 1994). Impairment ofthis function by VAD may contribute to lackof mucin secretion and liquefaction of the cor-nea seen in xerophthalmia (see Chapter 5).

Figure 3.8. Suggested roles of CRBPs and CRABPs. See text for details (Blomhoff,1994).


34

VITAMIN A IN HEALTH

no longer any risk in this regard to the fetus(Gerster, 1997; Wiegand, Hartmann, Hummler,1998; Ward, MacGowan, Hornby et al, 2000).To date it has not conclusively been demon-strated that human VAD causes congenitalmalformations. A number of individual casereports have been published but the associa-tion might well be coincidental and not causal.Although some of the synthetic retinoids areclearly teratogenic in man, there is very muchless evidence for a similar effect of large dosesof retinol (see Chapter 10). Some other as-pects of this topic are considered later in rela-tion to the safe use of vitamin A (see Chapters10 and 11). Many of the effects of vitamin Aare now known to be mediated by retinoid-regulated expression of homeobox genesand other pattern-forming genes. RAreceptors are closely involved (Ross, 1999).

Immune response

Many of the epithelial tissues are importantbarriers to infection and VAD impairs this func-tion in a nonspecific way. In addition, vitaminA is known to be involved in maintainingimmunocompetence in more specific ways.It helps to maintain the lymphocyte pool. Vi-tamin A also functions in T-cell-mediated re-sponses. Some aspects of the immune re-sponse, such as immunoglobulin production,previously considered unrelated are nowknown to be affected by retinoids (Semba,1998). Direct involvement of RA in the im-mune system has not been definitely estab-lished. It has been suggested (Buck, Ritter,Dannecker et al, 1991) that a third oxidizedmetabolite of retinol, 14-hydroxy-4,14-retroretinol is the active molecule in the immunesystem, but how it acts is not known.

Much of the evidence for the functioning ofvitamin A in the immune response comes fromevidence in both experimental animals andhuman subjects who are vitamin A deficient.This subject is consequently pursued furtherin Chapters 6 and 7.

Reproduction

Until recently it was believed that the maleand female reproductive organs shared incommon with the eye the fact that they werethe only tissues known to be unable to main-tain normal function when only retinoic acidis given. They appeared to require retinol fornormal spermatogenesis in the male and theprevention of placental necrosis and fetalresorption in the female rat (Thompson,Howell, Pitt, 1964). This was not so in birds(Thompson, Howell, Pitt et al, 1969). How-ever, high levels of CRABP have been foundin the testes (Ong, Newcomer, Chytil, 1994)and high doses of RA injected peritoneallysupport spermatogenesis (Van Pelt, De Rooj,1991). In addition, dietary RA appears to betaken up by testicular interstitial Leydig cells,as it supports testosterone production(Appling, Chytil, 1991). The mechanisms ofvitamin A action in reproduction are only nowbeginning to be understood.

Haemopoiesis

VAD in man and in experimental animals isconsistently associated with an iron deficiencytype of anaemia. It has been repeatedlyshown that in these circumstances in addi-tion to iron, vitamin A is required for a fullhaematologic response. The mechanism re-mains unclear. VAD might interfere with theabsorption, transport or storage of iron. Onthe other hand it might act directly on hae-mopoiesis, although that seems less likely(Sommer, West 1996, pp 150-162). The dem-onstration that RA is necessary for erythro-cyte differentiation implies that it controls theusage of iron (Pfahl, Chytil, 1996) (see alsoChapter 7).

Growth

Retinoic acid is known to play its hormone-like function in the control of growth and de-velopment of tissues in the musculo-skeletal


35

Chapter 3

system, just as it does elsewhere. In commu-nities subject to widespread VAD the occur-rence of many other adverse factors hasmade the demonstration of the retarding ef-fect of VAD difficult (Sommer, West, 1996, pp163-188) (see Chapter 7). One possiblemechanism for the influence on growth is thevery recent demonstration that both vitamin Aand retinoic acid produce rapid release ofcyclic AMP (adenosine monophosphate) andhuman growth hormone secretion (Djakoure,Guibourdeuche, Porquet et al, 1996).

Other functions

Energy balance

Heat production (thermogenesis) by mito-chondria in small collections of brown adiposetissue plays a part in the regulation of energybalance and consequently possibly in the con-trol of obesity. In mitochondria, an enzymenot present in white adipose tissue controlsthe local production of energy as heat. Thisenzyme is regulated by the sympathetic ner-vous system, but as has been recently shown(Alvarez, De Andres, Yubero et al, 1995) it isunder transcriptional regulation by RA.

Regulation of the dopaminergicsystem

RA plays a major role in the development ofthe fetal central nervous system. All-trans and9-cis RAs bound to their receptors in the brainand the pituitary gland regulate the expres-sion of the dopamine receptor D2R, which ispart of the dopaminergic system. Dopamineis a signalling molecule in the central nerv-ous system. It controls coordination of move-ment and also the synthesis of pituitary hor-mones. Parkinson’s disease results from adefect in the dopaminergic system. D2R-knockout mice lack these RA receptors anddevelop neurological damage similar to thatin Parkinson’s disease (Wolf, 1998).

Gap junctional communication

Gap junctions are narrow, hydrophilic poresconnecting the cytosol of two adjacent cells.There is evidence that gap junctions play arole in regulation of morphogenesis, cell dif-ferentiation, secretion of hormones, andgrowth. Effects on gap junctional communi-cation might be involved in carcinogenesisand teratogenesis. RA and its analogues ex-ert their effect by acting as ligands of nuclearreceptors RAR or RXR (see page 28 andStahl and Sies 1998).

Activities of carotenoids

Olson (1999) has classified the many activi-ties of carotenoids into functions, actions, orassociations but these divisions are not strictand rigid. In Table 3.8 an attempt is made tobring these together in outline form. The un-derlying mechanisms of some of these ac-tivities of carotenoids have been discussedin Chapter 2.

Table 3.8. Functions and actions ofcarotenoids

Functions•Some carotenoids are only known precur-sors of vitamin A and its derivatives

•Accessory pigments in energy transfer inphotosynthesis

•Phototropism in simple and higher plantforms

•Photoprotective role in bacteria and alsoman

•Plant growth regulation•Reproduction regulation in fungi

Actions•Quenching of singlet oxygen•Colour attractants in flowers for insect pol-lination

•Colouration of food for mankind


36

VITAMIN A IN HEALTH

Functions usually denote a more or lessclearly defined purpose. Through the conver-sion of provitamin A carotenoids to vitamin Ain the animal body this function is the mostevident one. Others, as indicated in Table 3.8,are less well understood in chemical terms.Actions, both biological and chemical, arereadily demonstrated but their consequencesare not so clear. Finally, associations ofcarotenoids are mostly known from epidemio-logical studies and usually have their impor-tance in relation to occurrence of diseases(see Chapter 10).

Human requirementsAlong with the requirements for other nu-trients those for vitamin A for humans ofeither sex, of different ages and in variousphysiological states, such as pregnancyand lactation, are kept under regular re-view. As mentioned earlier (see Chapter2) it is customary to express these in termsof Retinol Equivalents (RE)/day to take

account of the different activities in the bodyof retinol and the provitamin carotenoids. Ta-ble 3.9 gives Recommended Dietary Intakes(RDIs) for vitamin A from several differentsources.

RDIs like those shown in Table 3.9 are de-signed to prevent deficiency and to provide asafe intake for the large majority of a popula-tion (covering about ±2SDs from the mean).They were originally meant to ensure that, ifmet, deficiency would not occur, although aconsiderable proportion of a population wouldconsume more than they needed to.

However, evidence has recently emerged fora protective effect against some chronic dis-eases of increased amounts of antioxidant nu-trients, such as the carotenoids (see above andChapter 10). These possible beneficial effectshave not previously been taken into considera-tion when RDIs have been formulated. Theusual advice being given is to increase the in-take of fresh fruits and vegetables.

Table 3.9. Recommended Dietary Intakes of vitamin A (µg RE/day). ASG* (Age and sexgrouping) refers to data immediately on right only (McLaren, 1994)

ASG* FAO/WHO1 ASG Olson2 ASG NRC3 ASG UK4

0–1 350 375 375 3501–1.9 375 1–3 400 1–3 400

1–6 400 2–5.9 400 4–6 500 4–6 5006–10 400 6–9.9 500 7–10 700 7–10 500

10–12 500 M10–11.9 600 M11–51+ 1000 M11–14 60012–15 600 12–70+ 700 15–50+ 700

M 15–18+ 600F 15–18+ 500 F10–70+ 600 F11–51+ 800 F11–50+ 600

Pregnancy 600 6–9 mo +200 800 +100Lactation 850 0–5.9 mo +400 1st 6 mo 1300 +350

6+ mo +320 2nd 6 mo 1200

1 FAO/WHO, 1988 3 National Research Council, 19892 Olson, 1987 4 Panel on Dietary Reference Values, 1991


37

Introduction

Nutritional status, or nutriture, is an importantconcept that often tends to be misunderstood.It is sometimes thought to be represented bydietary intake, but this is not so. A financialanalogy may be helpful. A person may havean income, probably from a number ofsources, and also an expenditure on a vari-ety of things. If income exceeds expenditurethen that person’s financial balance or statusis positive (in the black) and if expenditureexceeds income the status is negative (in thered). In this analogy “income” may be re-placed by “nutrients in the diet” and “expendi-ture” by “utilization of nutrients by the body”.Then the resulting nutritional status (balance)may be either deficient (negative) or normal(positive). No analogy is perfect and whilstvery few indeed would object to having a veryhigh financial status, excess nutrient intake,including that of vitamin A, may be harmful.

Although, as pointed out above, assess-ment of dietary intake on its own is not equiva-lent to assessment of nutrient status, yet it isclearly closely related. Consequently themethodology of the assessment of dietaryintake of vitamin A is given some attention atthe end of this chapter.

It is clear that deviations of nutritional sta-tus from the usually accepted normal range(which is arbitrary to a considerable extent)

may vary in degree. The terms “mild”, “mod-erate” and “severe” deficiency are often used.Another useful division of status on the defi-ciency side is the use of the terms “subclini-cal” and “clinical” deficiency.

Nutritional status concerns some aspect ofthe state of the body and consequently thereare different types of possible test for the as-sessment of status. Table 4.1 outlines thetypes of test that have been employed withsome examples.

ASSESSMENT OF VITAMIN ASTATUS

Chapter 4

Table 4.1. Types of test of nutritionalstatus

Test Examples of use

Physical signs Later stages of anydeficiency disease

Physiological Dark adaptationfunction

Subclinical Conjunctival impressionstructural change cytology

Serum level of Serum retinolnutrient

Enzyme activity Erythrocytetransketolase

Urinary excretion Vitamin C, iodine

Body stores Relative dose response


38

ASSESSMENT OF VITAMIN A STATUS

Some of the different kinds of test are notapplicable in the case of assessment of vita-min A status at present. For example, thereare none for testing the activity of enzymesthat are dependent for their action on vitaminA, as is the case for some other vitamins.Measurement of urinary excretion of meta-bolic products of vitamin A metabolism, al-though theoretically possible, has not beenutilized until the present.The use of somaticmeasurements, such as weight and height,is the mainstay of detecting protein-energymalnutrition under field conditions. Althoughthere is increasing evidence that vitamin Adeficiency does have an effect on growth (seeChapter 7) there are many other nutritionalfactors and infections that act similarly. Thereis no aspect of retardation of growth that canbe linked specifically to deficiency of vitaminA. In fact, to describe a community as “un-derweight” or “stunted” contributes no under-standing of the nature of the underlyingcauses.

In the field of assessment of vitamin A sta-tus the first steps were taken when in 1974WHO convened an expert group to report onthe knowledge at that time of the problem ofVAD and xerophthalmia (WHO Expert Group,1976). A classification of the eye lesions was

agreed upon. With the limited experience atthat time some of these eye signs were cho-sen, together with serum retinol, and criteriaproposed for the identification of a problemof vitamin A deficiency of public health mag-nitude.

Several years later the first national pointprevalence survey of vitamin A deficiency wascarried out in Indonesia (Sommer, 1982). Asecond WHO Expert Group on the Control ofVitamin A Deficiency and Xerophthalmia(WHO Expert Group, 1982) was largely influ-enced by this study to make several altera-tions in the classification and the public healthcriteria (see Tables 4.2 and 4.3).

Table 4.2. Xerophthalmia classification byocular signs (WHO Expert Group, 1982)

Night blindness (XN)Conjunctival xerosis (X1A)Bitot’s spot (X1B)Corneal xerosis (X2)Corneal ulceration/keratomalacia

<1/3 of corneal surface (X3A)Corneal ulceration/keratomalacia

≥1/3 of corneal surface (X3B)Corneal scar (XS)Xerophthalmic fundus (XF)

Table 4.3. Criteria for assessing the pub-lic health significance of xerophthalmiaand vitamin A deficiency, based on theprevalence among children less than sixyears old in the community (WHO ExpertGroup, 1982)

MinimumCriteria prevalence

Clinical (primary)

Night blindness (XN) 1.0%

Bitot’s spot (X1B) 0.5%

Corneal xerosis 0 . 0 1 % and/or ulceration/keratomalacia (X2 + X3A + X3B)

Xerophthalmia-related 0 . 0 5 % corneal scars (XS)

Biochemical (supportive)

Serum retinol (vitamin A) 5 . 0 % less than 0.35 µmol/l (10 µg/dL)

ASSESSMENT OF VITAMIN A STATUSSIGHT AND LIFE MANUAL

39

Chapter 4

A more detailed consideration of the natureof the eye lesions and the way in which theymay be used in the assessment of VADD isthe subject of Chapter 5. More recent pro-posals for examination of visual functions as ameans of assessing subclinical vitamin A defi-ciency will be discussed later in this chapter.

This raises a point which requires somediscussion and explanation relating to theterms subclinical and clinical introducedabove. Whilst the division has its uses, thereis no clear-cut borderline between the two.Subclinical implies that there is no clinicalevidence of disease. The subject has no com-plaints of ill health and the examiner is un-able to elicit any physical signs of disease.Some indicators of vitamin A status span thisborderline between subclinical and clinical.This is the case for both impairment of retinalrod function and abnormal bulbar conjuncti-val histology. Both of these will be discussedin detail later, but it is useful at this point to

see how they span the subclinical-clinical di-vide (see Tables 4.4 and 4.5).

These tables show how impairment of func-tion and abnormality of structure, respectively,increase progressively with increasing degreeof deficiency.

Although the ocular lesions of xerophthal-mia are dealt with in the following chapters,after the subclinical stages of vitamin A defi-ciency and the tests that have been devel-oped for them, it is important to recognize that,in historical terms, the eye signs were stud-ied first. This is because xerophthalmia, at-tributable to severe deficiency, was first rec-ognized to be a serious public health prob-lem. It was the recognition that xerophthal-

Table 4.5. Progressive changes in con-junctiva and cornea, illustrating the sub-clinical–clinical divide

Test Abnormal appearance

Subclinical

Conjunctival In epithelial andimpression goblet cellscytology

Clinical

Conjunctival Drynessxerosis (X1A)

Bitot’s spot (X1B) Foamy, cheesy heapingup of keratinizedepithelial cells in inter-palpebral fissure

Corneal xerosis Hazy cornea (X2)

Keratomalacia Liquefaction of part or (X3) all of corneaTable 4.4. Increasing impairment of reti-

nal rod function, illustrating the subclini-cal–clinical divide

Tests of retinal Abnormalrod function response

SubclinicalDark adaptometry Abnormal final rod

threshold

Vision restoration Delayed responseafter bleaching

Pupillary contraction Failure of contractionin low illumination

ClinicalNight blindness Subjective

impairment ofvision in lowillumination


40


mia was the most common cause of blind-ness in young children around the world, asindeed it still is, that justified all the effortsthat were expended to control it from the1960s onwards. When in the 1980s it becameevident that subclinical deficiency was asso-ciated with a significant increase in youngchild mortality (see Chapter 6), what might betermed a second wave of concern resulted.This realization provided the impetus for re-search into reliable methods for the assess-ment of vitamin A status at the subclinical level.

Indicators for the assessmentof vitamin A status at thesubclinical levelOver the past decade or so WHO has playeda leading role in bringing together the resultsof research in this field (WHO, 1996). For adetailed account of the technical and logisticalaspects of this subject this report and someothers cited in Further Reading should beconsulted. It is the present purpose to give abalanced overview, to indicate the presentstate of the art and to suggest how it mightdevelop in the near future. The recommen-dations of the 1996 report will need to be triedand tested in field studies, just as those ofthe 1976 report were.

Serum retinol (Pilch, 1987)

The level of retinol in serum is underhomeostatic control over a wide range of bodystores and reflects these stores only whenthey are very high or very low. Thus an iso-lated serum retinol value is not an accurateindicator of vitamin A status. Serum retinol isbest used when a frequency distribution canprovide useful information about the statusof a population and about response to an in-tervention programme. The disadvantagesdescribed for the RDR tests regarding bloodsampling and the effect of infections (seeChapter 9) apply equally.

In the past it has usually been consideredthat a serum retinol level <0.35 µmol/l was“deficient” and <0.70 µmol/l was “low”. TheWHO 1996 report recommended to retain the“low” value at 0.70 µmol/l and to consider thisconsistent with the presence of a subclinicaldeficiency status. It proposed the followingcut-off points: 2–10% mild; 10–20% moder-ate; >20% severe (see Table 4.7, p 48). Therehas to be a question raised about the point atwhich the mild subclinical deficiency statushas been set; i.e. >2%. In the United States(Pilch, 1987) and in the United Kingdom(Gregory, Collins, Davies et al, 1995) nutri-tion surveys that included serum retinoldeterminations on large numbers of preschoolage children have been conducted (Figure4.1). In both instances values for both sexesand all age groups fall well within the presentdefinition of a mild subclinical vitamin A defi-ciency problem. If true this would suggest thatall countries would have some degree of sub-clinical vitamin A deficiency. In view of theserious consequences of this state in termsof increased risk of morbidity and mortality itwould imply the need for universal vitamin Aintervention.

Serum retinol-binding protein(RBP)

Several studies (Blaner, Piantedosi, Gamble,1999; Donnen, Dramaix, Zihindula et al, 1999;Almekinder, Manda, Kumwenda et al, 1999)have recently shown that measurement ofserum RBP correlates very closely with se-rum retinol (see p 7).

The immunodiffusion technique commonlyemployed is much simpler and cheaper thanHPLC usually used for retinol. A simple, por-table microtechnique for measuring holo-RBPusing a fluorometer has been introduced byCraft (1999).


41

Chapter 4

RBP/TTR molar ratio

This ratio has been introduced in an attemptto assess vitamin A status in the presence ofinflammation (Rosales, Ross, 1998). In theacute phase response (APR) (see also Chap-ter 9) RBP in plasma falls, as it does in VAD.On the other hand, TTR (transthyretin), towhich retinol is also bound in plasma, falls inthe APR but is unaffected by VAD. Studies inexperimental animals and children with seri-ous infections have indicated that a low mo-lar ratio of RBP/TTR can distinguish VAD inthe presence of infection. Recently, furtherwork was carried out in malaria (Rosales,Topping, Smith et al, 1999) and negative re-sults were reported from Congo (Donnen,Dramaix, Zihindula et al, 1999).

RAG hydrolysis test

Retinoyl β-glucuronide (RAG) is a naturallyoccurring metabolite of vitamin A. It is highlyactive biologically with little toxicity. It may

have therapeutic applications (Barua, 1997).When administered orally to rats with ad-equate vitamin A status RAG is only slowlyhydrolyzed to RA, but in animals with VADRA appears in the plasma in high concentra-tions. Recent work (Olson, Barua, Kaul et al,1999) found that the RA response was pro-portional to the degree of VAD. This appearsto be a promising new test.

Assessment of body reservesIn the past there was considerable advocacyfor the concept of relying upon the estimationof vitamin A concentration in the livers of pa-tients at postmortem as a means of charac-terizing the vitamin A status of a population(WHO Expert Group, 1976). In practice thishas proved difficult, except in the context ofresearch. Furthermore, newer indirect anddirect assessment methods have come tooccupy centre stage.

Figure 4.1. Distribution of plasma retinol in children aged 1.5 to 4.5 years (Gregory,Collins, Davies et al, 1995)


42


Indirect assessment of liver stores

In Chapter 3 it was mentioned that apo-RBPaccumulates in the liver when retinol is in shortsupply. Once retinol becomes available holo-RBP is released into the circulation. This phe-nomenon is the basis of the relative dose-response tests. The magnitude of the retinolreleased from the liver when a test dose isgiven is proportional to the degree of priordepletion of the liver.

Relative dose response (RDR)(Underwood, 1990)

A fasting serum retinol is measured (A0). Vi-tamin A as 450–1000 mg retinyl ester in oilysolution is given orally. Five hours after dos-ing, another serum retinol is measured (A5).

The RDR is calculated as follows:

RDR = (A5 – A0) x 100/A5

If the result of the calculation is >20% thenthe test is considered to be positive, i.e. storesare deficient. It has been shown that a resultof 20% in the test is approximately equiva-lent to a liver reserve of 0.07 µmol/g. Twoblood samples are required.

Modified relative dose response(MRDR) (Tanumihardjo, Koellner, Olson 1990)

This test employs a metabolite of vitamin A,3, 4-didehydroretinyl acetate (DR, also knownas dehydroretinol, vitamin A2). DR binds toRBP and appears in the serum after a testdose is given if liver reserves of vitamin A arelow. A single oral dose of DR is given andonly one blood test is required, 4–6 hours af-ter the dose.

Serum concentrations of retinol (SR) anddehydroretinol (SDR) are measured. The mo-lar ratio is calculated in the following way:

MRDR = SDR/SR

An MRDR-value is considered to be abnor-mal when the above ratio is >0.06.

Serum 30-day dose response (+S30DR)(Flores, Campos, Aranjo et al, 1984)

This test is similar to the RDR describedabove but the second blood sample is taken30–45 days after the first. It has been used atthe population level and has been used formonitoring the effectiveness of interventionprogrammes for improving vitamin A status.

Advantages

It is known from work in experimental animalsthat in depletion studies vitamin A levels inthe liver fall steadily over a considerable pe-riod of time before serum retinol levels beginto fall and even longer before any functionalor structural changes begin to occur. Thesetests appear therefore to be good measuresof subclinical VAD.

Disadvantages

Blood samples are required. In manypopulations this may not be acceptable forcultural reasons and in view of the risks oftransmitting HIV, hepatitis etc. The single sam-ple for MRDR raises less of a problem thanthe two samples required for the RDR.

Retinol-binding protein is among a numberof proteins that take part in the acute phasereaction in infection and inflammation. Therelease of RBP from the liver is repressed bya number of factors that are likely to be widelyprevalent in the communities under study.These include acute and chronic infectionsand infestations and protein-energy malnu-trition. This subject is considered in moredetail later (see Chapter 9). Other than in re-search projects the means for estimating se-


43

Chapter 4

rum retinol on a routine basis are not readilyavailable. The compound DR, used in theMRDR test, is costly and is not readily avail-able (WHO, 1996).

Recommendations and comments

The WHO 1996 report proposes cut-off pointsof prevalence for each of the above three re-sponse tests that are similar. These are to beused to indicate respectively “mild”, “moder-ate” and “severe” public health problems. Thecut-off points given are: <20%; 20–<30% and≥30%. It should be noted that according tothis any % prevalence will constitute at leasta mild problem (possibly >2% has been omit-ted in error; see page 7, table 2 of the report)(see table 4.7, p 48). The same commentapplies to the “mild” category of breast milkretinol (<10%). In the case of “mild” nightblindness 0 –1% implies that the presence ofa single case will always indicate the pres-ence of a public health problem.

Several recent studies have made compari-sons between various methods of assess-ment of vitamin A status (Rice, Stoltzfus, deFrancisco et al, 2000; Apgar, Makdani, Sowellet al, 1996; Wahed, Alvarez, Khaled et, al1995; de Pee, Yuniar, West et al, 1997).

Deuterated-retinol-dilutiontechnique

This technique using the stable isotope ofhydrogen, deuterium, measuring total bodyvitamin stores indirectly but quantitatively isbeing used increasingly in research projects(Haskell, Mazumder, Peerson, 1999; Ribaya-Mercado, Mazariegos, Tang et al, 1999;Haskell, Handelman, Peerson et al, 1997).A dose of vitamin A labelled with the stableisotope deuterium is given by mouth andabout three weeks allowed for equilibrationwith the reserves of the body. Blood is sam-pled at this point and extent of dilution of the

labelled tracer relates to the amount ofendogenous reserves. Olson (1997) hasreviewed the difficulties inherent in this newmethod but describes isotope-dilution tech-niques like this as “a wave of the future inhuman nutrition”.

Breast milk vitamin Aconcentration

It has long been known that the concentra-tion of vitamin A in the breast milk of under-nourished mothers is low. The proposal to usethis as an indicator of vitamin A status of acommunity is relatively new and needs to betested under varying conditions. It has theadvantages of being non-invasive, readilyacceptable and the sample is easy to collect.It is important to follow standardized meth-ods of collection of the sample, and themethod of expression of the concentration ofvitamin A should be agreed upon. Results todate suggest that in vitamin A-sufficient popu-lations average breast milk concentrationsrange from 1.75 to 2.45 µmol/L. In a vitaminA-deficient population average values arebelow 1.4 µmol/L. The borderline of defi-ciency in a population is suggested to be<1.05 µmol/L. Prevalence rates proposed aremild <10%; moderate 10–25%; severe ≥25%(see Table 4.7, p 48).

In one study in Indonesia (Stoltzfus, Hakimi,Miller et al, 1993) there was a close correla-tion between breast milk concentrations be-low 1.05 µmol/L and the prevalence of posi-tive RDR tests in infants 6 months of age.More recently in Bangladesh a comparisonof serum retinol, MRDR and breast milk foundthat overall the most responsive indicator topost-partum maternal vitamin A supplemen-tation was the measurement of breast milkvitamin A per gram of fat in casual breast milksamples (Rice, Stoltzfus, de Francisco et al,2000).


44


Histological indicator[Conjunctival ImpressionCytology (CIC)]In Chapter 3 attention was drawn to the ma-jor role played by vitamin A in cellular differ-entiation. The abnormal changes that occurwhen vitamin A is deficient have been docu-mented best for the conjunctiva and to alesser extent for the cornea. Basically thereis a drying process, xerosis, which may ulti-mately in the conjunctiva lead to the devel-opment of a Bitot’s spot (X1B) (see Chapter5). The earlier change that is visible with thenaked eye, called conjunctival xerosis (X1A),is much less distinctive (see Chapter 5). Thisin turn is preceded by lesser degrees ofchange that are at the subclinical level.

With the introduction of the technique of CIC(Wittpenn, Tseng, Sommer, 1986) and a modi-fication termed Impression Cytology withTransfer (ICT) (Luzeau, Carlier, Ellrodt et al,1988) it has become possible to study thesevery early changes under a microscope. De-tails of the techniques that have been advo-cated are given in a training manual (Wittpenn,West, Keenum et al, 1988), in several originalpapers and also in the WHO 1996 report(WHO, 1996). In essence, a normal impres-sion of conjunctival cells when stained willshow one or more sheets of small regular epi-thelial cells and numerous mucin-secretinggoblet cells. In VAD the epithelial cells becomeflattened, enlarged and reduced in number.The goblet cells are markedly reduced innumber or absent (see Figures 4.2–4.7).

Table 4.6 shows the relationship betweenthe prevalence of abnormal CIC and vitaminA status assessed by some other indicators.Unfortunately when the results of CIC havebeen compared with those of biochemicaltests there has been little correspondence(Tanumihardjo, Permaesih, Dahro et al, 1994;Makdani, Sowell, Nelson et al, 1996).

Limitations

Difficulties have arisen over the significanceof some of the appearances. While there isno doubt about those described above forclearly normal and clearly abnormal impres-sions, the vast majority of impressions willnot be so distinct. Standardization of exist-ing interpretation schemes is required if thetechnique is to come into widespread use(WHO, 1996). The test is well accepted af-ter the age of about 3 years, but has posedproblems in younger children. The presenceof acute conjunctivit is and trachoma(Lietman, Dhital, Dean, 1998) interferes withCIC.

More recent experience suggests thatConjunctival Impression Cytology with Trans-fer (CICT) identical with ICT above is the pref-erable technique (Chowdhury, Kumar, Gang-uly et al, 1996). These investigators reportedthat healing after vitamin A dosing takes fromabout 70 to 110 days to be completed(Chowdhury, Kumar, Ganguly, 1997). Thismay seem to be a long time for a minimallesion such as early xerosis and keratiniza-tion of the conjunctiva, especially in compari-son with healing of the more severe clinicallesions (see p 64). In this regard it should beremembered that microscopic techniques arelikely to be more precise than clinical obser-vations. CIC is being used increasingly in clini-cal ophthalmology and new refinements areconstantly being introduced (Thiel, Bossart,Bernauer, 1997).

Impaired dark adaptationIt will be recalled that the rod cells of the retinacontain vitamin A in the form of 11-cis retinalbound to opsin to form rhodopsin (see Chap-ter 3). These cells are photosensitive underconditions of low levels of illumination (nightor scotopic vision). Table 4.4 above showedthe various stages of increasing deficiency atwhich different kinds of testing may be applied.


45

Chapter 4

4.2. Normal conjunctival impression withabundant goblet cells, sheets of small epithe-lial cells, and mucin spots [periodic-acid Schiff(PAS) and Harris’ haematoxylin, x 160].

4.3. Higher power of normal conjunctiva,showing contrast between PAS-positive gob-let cells and epithelial cells (PAS and Harris’haematoxylin, x 400).

4.4. Abnormal conjunctival impression withcomplete loss of goblet cells and mucin spots,along with appearance of enlarged epithelialcells (x 100).

4.5. Higher power of abnormal, enlarged con-junctival cells (PAS and Harris’ haematoxy-lin, x 400).

4.6. PAS-positive mucin spots representing“impressions” of goblet cells on conjunctivalsurface (PAS and Harris’ haematoxylin,x 400).

4.7. Impression cytology from normal child show-ing transition from abundant normal epithelium(lower left) to abnormal epithelium (upper right).Specimen was graded as normal (x 100).

Figure 4.2–4.7 Conjunctival impression cytology (Wittpenn, Tseng, Sommer, 1986).


46


Night blindness

This is the most advanced stage of deficiencythat can be related to rod dysfunction. In asubject able to cooperate this is the subjec-tive sensation of inability to see adequatelyin poor illumination, such as at dusk. It issometimes erroneously termed hemeralopia(Greek hemera, day) or nyctalopia (Greeknyct, night; alaos, obscure). Dusk blindnesswould be a better term.

The dark adaptometer is a standard pieceof ophthalmology department equipment forexamination of night vision. Some versionsare available for use under field conditions.These may be used for investigating the prob-lem of night blindness in cooperative subjectssuch as school children and pregnant andlactating women, among whom a high preva-lence has been reported in some countries(Sommer, West, 1996, p 338).

In young children, the major vulnerablegroup of VADD, direct observation and an in-terview have usually been used. A standard-ized interview of the child’s guardians hasbeen developed (Sommer, Hussaini, Muhilalet al, 1982) and use is made of the fact thatfrequently in endemic areas terms occur inthe local language. These often liken poorvision at dusk to “chicken eyes” (chickenshave no rod cells in their retina) or Bitot’s spotsto “fish scales”. If the child is old enough towalk, it may be observed to stumble in a roomat dusk, or it may fail to grasp a proffered toyor sweet (see also Chapter 5).

Vision restoration time (VRT)

The ability of the bleached eye to recognizea letter under low levels of illumination hasbeen measured in school-age children inThailand (Udomkesmalee, Dhanamitta,Sirisinha et al, 1992). From this study it ap-

Table 4.6. Abnormal conjunctival impression cytology and vitamin A status (Natadisastra,Wittpenn, Muhilal et al, 1988)

Vltamin A status Patient characteristics Number AbnormalCIC (%)

Definite deficiency • XN(+) plus X1B(+) responding to vitamin A• Serum retinol <20 µg/dL 14 93

Probable deficiency • Bilateral X1B(+) responding to vitamin A 22 82

Probable deficiency • XN(+) responding to vitamin A• serum retinol <20 µg/dL 15 67

Possible deficiency • Unilateral X1B(+) [XN(–)] responding to vitamin A 8 50

Possible deficiency • Normal exam• Serum retinol <20 µg/dL 26 46

Borderline deficiency • XN(+) plus retinol ≥20 µg/dL or normal exam and retinol 20–25 µg/dL 43 14

“Normal” • Normal exam• Serum retinol >25 µg/dL 18 6


47

Chapter 4

peared that zinc was a more important deter-minant of VRT than vitamin A (see also Chap-ter 7). The test is applicable only to older chil-dren with some degree of literacy.

Pupillary threshold

This test is based on the fact that the weak-est threshold of light visible in the dark-adapted state is approximately of the sameintensity as that needed to cause pupillarycontraction. The pupils of night blind subjectsfail to react or constrict normally in low illumi-nation. Children as young as one year oldhave been studied successfully (Congdon,Sommer, Severns et al, 1995). Further test-ing in children with VAD in India (Sanchez,Congdon, Sommer et al, 1997) and of preg-nant women in Nepal (Congdon, Dreyfuss,Christian et al, 1999) has been distinctly prom-ising. The test has proved readily acceptable,is associated closely with serum retinol, andresponds to vitamin A supplementation. It alsohas the advantages of being non-invasive,applicable to young children and sensitive atthe subclinical stage of VAD.

Table 4.7 indicates how some of these bio-logical indicators may be used to grade dif-ferent levels of subclinical VAD (WHO, 1996).

Assessment of dietary intakeof vitamin A

As mentioned above, this is strictly speakingnot a measure of vitamin A status but can pro-vide useful and complementary informationnot available otherwise. It has the advantagesof not being invasive, expensive or compli-cated, large numbers of subjects can be read-ily targetted and a profile of a population ob-tained. Knowledge of available and utilizedsources of vitamin A can be collected that mayprove to be of value in subsequent dietaryinterventions. Two organizations, InternationalVitamin A Consultation Group (IVACG ) and

Helen Keller International (HKI) have beenlargely instrumental in promoting the devel-opment of assessment methods and fieldstudies.

IVACG (1989) introduced a simplified di-etary assessment (SDA) as a method to iden-tify and monitor groups at risk of suboptimalvitamin A intake. Intake information is obtainedby past 24-hour dietary recall and by historyof the usual pattern of consumption of vita-min A-rich foods during the previous month.Food quantities were estimated. Some expe-rience with this method has found it to be dif-ficult, time-consuming, or poorly correlatedwith measures of vitamin A status. The semi-quantitative 24-VASQ (twenty four hoursvitamin A semiquantitative) method is partlybased on the IVACG method. It estimatesvitamin A intake using 24 h recall data, usesindividual ingredients instead of dishes, andfrom four sources – vegetables, fruits, ani-mal foods and fortified foods. It has been usedsuccessfully in Indonesia, Bangladesh andNepal (de Pee, Bloem, Kiess et al, 1999; dePee, Bloem, Halati, 1999).

The Helen Keller International Food Fre-quency Method (HKI FFM) was introduced in1993 (Rosen, Haselow et al, 1993). Thismethod studies the diet of children 1–6 yearsof age. A score is assigned to each childbased on the number of rich sources (> 100RE/ 100 g vitamin A content), both animal andplant, consumed during the previous week,with amounts ignored.

Animal milk was ignored in the originalmethod, but subsequently it has been shownthat in some areas this can provide 5–18% ofthe “safe” RDI and should be considered. Ex-perience with five communities in each thePhilipinnes, Tanzania and Guatemala, usingserum retinol <20 µg/dL as deficient, foundcorrect classification as deficient in 73.3%, buta high false-positive rate of 42.9% (Sloan,Rosen, Paz, 1997).


48


Unfortunately, the uncertainty that now ex-ists about the bioavailability and biocon-version factors for provitamin A carotenoids(see Chapter 2) overshadows these and allmethods of assessment of dietary vitamin Aintake. Until these matters are resolved re-sults of field work will have to be interpretedwith caution.

Ecological indicatorsThe WHO 1996 report introduced the conceptof the use of what it termed “Ecological and re-lated indicators associated with risk of VAD”. Itrecognized that these indicators could not beused alone to replace biological indicators(those described above and specifically relatedto VAD) or to define whether a population has aVAD problem of public health significance. Itgoes on to describe and to define these indica-tors. Table 4.8 shows these indicators and howthey may be used in VAD surveillance.

Table 4.7. Biological indicators of subclinical vitamin A deficiency in children 6–71 monthsof age (WHO, 1996)

Prevalence below cut-offs to define a publichealth problem and its level of importance

Indicator(cut-off) Mild Moderate Severe

FunctionalNight blindness >0–<1% ≥1–<5% ≥5%(present at 24–71 months)

BiochemicalSerum retinol ≥2–<10% ≥10–<20% ≥20%(≤0.70 µmol/L)

Breast milk retinol <10% ≥10–<25% ≥25% (≤1.05 µmol/L or ≤8 µg/g milk fat)

RDR (≥20%) <20% ≥20–<30% ≥30%

MRDR <20% ≥20–<30% ≥30% (ratio ≥0.06)

+S30DR (≥20%) <20% ≥20–<30% ≥30%

HistologicalCIC/ICT <20% ≥20–<40% ≥40%(abnormal at 24–71 months of age)


49

Chapter 4

The WHO 1996 report proposes that a pub-lic health problem exists when the criteria setin Table 4.7 are met in the case of at leasttwo of the biological indicators, or when onebiological indicator is supported by at leastfour of the ecological indicators in Table 4.8(two of which are nutrition- and diet-related).

The 1996 WHO report suggests a tentativeranking of the biological indicators discussedhere for usefulness in various activities (seeTable 4.9). This is bound to be very subjective.It is disappointing to see how low CIC/ICT ranks,

as, on a priori grounds, it might be consideredone of the most promising tests of all.

In conclusion it has to be said that now thereis available a plethora of methods of as-sessment of vitamin A status at the sub-clinical level. Most have been developed onlyin the last two decades at most. Each tendsto have its advocates and this makes deci-sions about choice of method very difficult.This is expecially so while discrepancies con-tinue to be reported between the results withthe various tests.

Table 4.8. Ecological indicators of areas/populations at risk of VAD: Nutrition- and diet-related indicators* (WHO, 1996)

Indicator Suggested prevalence

Breast-feeding pattern<6 months of age <50% receiving breast milk≥6–18 months of age <75% receiving vitamin A-containing foods

in addition to breast milk, 3 times/week

Nutritional status (< –2SD from WHO/NCHSreference for children <5 years of age)

Stunting ≥30%Wasting ≥10%

Low birth weight (<2500 g) ≥15%

Food availabilityMarket DGLV1 unavailable ≥6 months/yearHousehold <75% households consume

vitamin A-rich foods 3 times/week

Dietary patterns6–71 months old children, <75% consume vitamin A-richpregnant/lactating women foods at least 3 times/week

Semi-quantitative/qualitative Foods of high vitamin A content eatenfood frequency <3 times/week by ≥75% vulnerable groups

* There are also illness-related indicators not reproduced here1 Dark Green Leafy Vegetables


50


Table 4.9. Relative ranking on a population base of some biological indicators usefulfor various surveillance purposes (WHO, 1996)

Indicator Risk Targeting Evaluatingassessment programmes effectiveness

Night blindness +++ +++ +++

Breast milk retinol (lactating mothers and breast-fed infants) ++ +++ ++

Serum retinol ++ + ++

RDR/MRDR +++ +++ +++

CIC/ICT + -- --

+S30DR -- -- +++


51

Chapter 5

XEROPHTHALMIA

DefinitionsThe term xerophthalmia literally means “dryeye”. However, dryness or xerosis, which alsoaffects other parts of the body (see Chapter3), is only part of the abnormal process un-dergone by the eye in vitamin A deficiency.Xerosis is confined to the epithelial structuresof the eye, the conjunctiva and the cornea.Only the conjunctiva covering the globe,known as the bulbar conjunctiva, and not thatlining the eyelids or the palpebral conjuncti-va, is affected by xerosis. In addition, the cor-nea undergoes other changes, known askeratomalacia, as will be described later. Af-ter recovery from acute vitamin A deficiencythat affects more than just the most superfi-cial layer of the cornea, scars of varying ex-tent and depth remain (XS).

In vitamin A deficiency the retina is also af-fected. The rhodopsin system in the rod cellsof the retina is much more sensitive to defi-ciency than is the iodopsin system in the conecells. As a result, rod function is impaired earlyon, resulting when sufficiently marked in im-pairment of night vision. Impairment of conefunction, i.e. day vision and colour vision, israrely seen clinically. There have been a fewreports of structural damage to the rod cellsin the retina.These have been calledxerophthalmic fundus (XF).

All of these eye changes are included inthe term xerophthalmia. In other words,xerophthalmia is synonymous with all of the

clinical signs and symptoms that affect theeye in vitamin A deficiency. The various ocu-lar appearances in xerophthalmia were clas-sified by WHO in 1976 (WHO Expert Group,1976) and modified in 1982 (WHO ExpertGroup, 1982). Criteria of a public health prob-lem were also developed. These tables werereferred to previously (see Chapter 4, Tables4.2 and 4.3) but for convenience they are re-produced here (see Tables 5.1 and 5.2).

To a considerable extent the ocular signsin Table 5.1 have been listed in an increasingorder of severity. This means that retinal func-tion tends to be impaired before xerosis af-fects first the conjunctiva and then the cor-nea. Liquefaction of the cornea, of increas-

Table 5.1. Xerophthalmia classification byocular signs (same as Table 4.2)

Night blindness (XN)

Conjunctival xerosis (X1A)

Bitot’s spot (X1B)

Corneal xerosis (X2)

Corneal ulceration/keratomalacia<1/3 of corneal surface (X3A)

Corneal ulceration/keratomalacia≥1/3 of corneal surface (X3B)

Corneal scar (XS)

Xerophthalmic fundus (XF)


52

XEROPHTHALMIA

ing severity, is a very late stage normally.Corneal scars are not part of the active defi-ciency process.They may be considered tobe stigmata of previous deficiency, providingthere is circumstantial evidence suggestiveof vitamin A deficiency as their cause. Thesecharacteristics are discussed later. Thexerophthalmic fundus is a rarity and does notfit neatly into the classification (see later).

Background

There are two other aspects of the subject ofthe definition of xerophthalmia that need tobe made quite clear. Firstly, there are othercauses of xerophthalmia than dietary vitaminA deficiency, the epidemic disease that pri-

marily affects young children in developingcountries and that is our main concern in thisManual. These cases arise sporadically andare caused by various defects in the utiliza-tion of vitamin A within the body. Most of theseare quite uncommon. They are instances ofsecondary or endogenous VAD and are con-sidered later in Chapter 10.

The other aspect of the subject that needsto be pointed out is that some of the eyechanges may be caused by diseases that arenot related to vitamin A deficiency. For exam-ple, night blindness is a symptom of severalrare degenerative disorders of the retina. It isalso a main feature of a not uncommon blind-ing disease called retinitis pigmentosa. Forthe most part these diseases do not respondto treatment with vitamin A (see Chapter 10).

Dryness of the conjunctiva and cornea isalso a feature of several diffuse connectivetissue disorders, one of which is Sjogren’ssyndrome. The xerosis results from atrophyof the secretory epithelium of the lacrimalglands and does not respond to vitamin A.

There are several facts that shed light onthe way in which xerophthalmia has tendedto be neglected over the years. For reasonsthat are not clear xerophthalmia was usuallynot included among the classical vitamin de-ficiency diseases when these were first iden-tified in the 19th and early 20th century. Ber-iberi, scurvy, pellagra and rickets were usu-ally considered together and xerophthalmiawas rarely included (Funk, 1912). Eventhough fat-soluble A was the first vitamin iden-tified (McCollum, Davis, 1915) and was there-fore given the first letter in the alphabet,xerophthalmia was not studied in detail at thetime. Night blindness and Bitot’s spots tendedto be described in isolation from the blindingchanges of corneal xerophthalmia. It may bethat scientists and general physicians did notfeel competent to examine the eye and dealwith eye disease. It is of interest that the only

Table 5.2. Criteria for assessing the pub-lic health significance of xerophthalmiaand vitamin A deficiency, based on theprevalence among children less than sixyears old in the community (same as Ta-ble 4.3)

MinimumCriteria prevalence

Clinical (primary)

Night blindness (XN) 1.0%

Bitot’s spot (X1B) 0.5%

Corneal xerosis 0 . 0 1 % and/or ulceration/keratomalacia (X2 + X3A + X3B)

Xerophthalmia-related 0 . 0 5 % corneal scars (XS)

Biochemical (supportive)

Serum retinol (vitamin A) 5 . 0 % less than 0.35 µmol/l (10 µg/dL)

XEROPHTHALMIASIGHT AND LIFE MANUAL

53

Chapter 5

vival. These matters are the topic of Chapter6. This new knowledge has given a tre-mendous impetus to the drive to control andeventually eradicate vitamin A deficiency ofall degrees. This important and fully justifiedshift of emphasis in recent times must not,however, be allowed to draw attention awayfrom the fact that large numbers of youngchildren still suffer visual impairment as theresult of consuming a diet deficient in vitaminA and its precursors.

It is interesting to note that this revolutionin the thinking about the significance of vita-min A deficiency in man is part of a generalpattern also seen in other micronutrient defi-ciency diseases. This is particularly true ofthe two elements iron and iodine, which arenow very commonly associated with vitaminA and termed Micronutrient Disorders (WHO,1992). Iron deficiency was for long consid-ered to be of little more public health signifi-cance than an important cause of anaemia.Now we know that work capacity may be se-riously affected and in the young mentaldevelopment and ability to profit from school-ing may be impaired. In the case of iodinethe term Iodine Deficiency Disorders (IDD)has been coined. It is now known that en-demic colloid goitre is not the most significantconsequence for public health of iodine defi-ciency. Development of the brain in fetal andearly postnatal life may be retarded and rela-tively minor degrees are much more commonthan clinical cretinism. Other examples ofexpansion in recent years of the significanceof micronutrient deficiency are provided byvitamins D and K and the element zinc.

Night blindness (X1N)It will be recalled that the subject of retinaldysfunction was considered previously in con-nection with indicators of VAD (see Chapter4). As shown in Table 4.3 night blindness isthe most extreme form of retinal dysfunction;sufficiently severe to cause subjective impair-

vitamin deficiency to have reached epidemicproportions and to persist at these levels to-day is xerophthalmia. This historical aspectof VADD has been discussed recently(McLaren, 1999).

Corneal xerophthalmia is usually associ-ated with a severe degree of vitamin A defi-ciency which is often accompanied by severegeneralized malnutrition (PEM) and seriousinfections (McLaren, Shirajian, Tchalian et al,1965). Death is the most likely outcome atthis late stage, even in adequately treatedpatients. In this way death “removes” the prob-lem of long-term care of the blinded survivors.Follow-up over a period of one year after thediagnosis of corneal xerophthalmia hasshown that only about 40 % survive (tenDoesschate, 1968). Of these survivors about25 % remain totally blind and 50–60 % arepartially blind. It is, consequently, uncommonto find a high proportion of inmates of blindschools in developing countries havingxerophthalmia as the cause of their blindness.Even those that do recover from acute se-vere vitamin A deficiency when young arelikely to fare badly in the community. In suchcircumstances there is little possibility of theirreceiving an education. Without special train-ing they will be unable to do any work andtheir survival constitutes a continuing burdenon the family and the community at large.

The close association between vitamin Adeficiency and susceptibility to infections wasnoted in both experimental animals and inchildren many years ago (Semba, 1999;Sommer, West, 1996, pp 62-98). It was onlyin the past twenty years or so that this phe-nomenon was explored systematically andscientifically at the community level. This re-search has resulted in, among other things,an appreciation of the public health impor-tance of subclinical vitamin A deficiency in thecontext of the increased susceptibility ofyoung children to suffer from various infec-tions and also their diminished chance of sur-


54

XEROPHTHALMIA

ment of vision at night. As an indicator ofVADD it has both advantages and disadvan-tages. On the positive side, tests arenoninvasive and some of them may be ap-plied by investigators with no specialized oph-thalmological training. In this category arequestionnaires and observation of the per-formance of young children under conditionsof low illumination.

On the negative side, the objective testingof night vision requires sophisticated and ex-pensive equipment, operated by skilled oph-thalmological staff. The subjects need to beof sufficient age and education to cooperatefully in the testing. This applies to darkadaptometry, rod scotometry, and to someextent to electroretinography, which is lesssensitive.

The most promising of the new tests of darkadaptation is measurement of the pupillarythreshold (see Chapter 4). This has been pio-neered by one group and is still undergoingfield trials. Some of its advantages and dis-advantages were discussed previously. Infield studies the most practical method ofdetecting night blindness at the present timeis by interview, and WHO has recommendeda scheme for this purpose (see Table 5.3).

This scheme may increase the specificityand reduce the error of classification solelyon the basis of familiarity with the term. Theuse of focus group discussions in differentsituations may be useful in identifying localterms for night blindness and the specificitywith which they are useful for identifying VAD.

One study in Bangladesh (Hussain, Kvale,Odland, 1995) compared over a hundred chil-dren aged 2–15 years and reported to be nightblind by their parents with a similar numberof matched controls. Both groups received aneye examination, test of scotopic vision by aluxometer – a simple form of dark adaptom-eter – and serum retinol level. Although there

Table 5.3. Scheme for the classification ofnight blindness by interview (WHO, 1996)

1) Does your child have any problem seeingin the daytime?

2) Does your child have any problem seeingat nighttime?

3) If (2) = yes, is this problem different fromother children in your community? (Note:this question is particularly appropriatewhere VAD is not very prevalent.)

4) Does your child have night blindness (uselocal term that describes the symptom)?

was fairly close correlation between the twomethods of diagnosing night blindness, theparents’ report appeared to be less sensitive.

The occurrence of names for night blind-ness in local languages suggests that thisrather distinctive phenomenon is occurringwith some regularity in a community. Thecommonest terms used are “night eyes” and“chicken eyes” (chicken have no rods andare therefore night blind). Night blindness issuch a distinctive symptom that it has givenrise to some interesting stories about its oc-currence. For instance, many years ago itoccurred in fishermen in Newfoundland inCanada. They learned to bind up one eyebefore they went out in the bright glare onthe ocean. The retina of the exposed eyewould become bleached and vitamin A defi-ciency prevented regeneration of rhodopsin.Fishing could continue by unbinding theother eye.

Little night blindness is detected in veryyoung children because the effects of de-ficiency only become evident when thechild tries to move around at dusk. Fromabout 2 years onward rates of night blind-ness tend to rise, because of increased


55

Chapter 5

activity. Evidence has accumulated in re-cent years to show that school age chil-dren and pregnant and lactating women(Khan, Haque, Khan, 1984; Katz, Khatry,West et al, 1995) are also vulnerablegroups in which the measurement of rodvision may be a useful means of assess-ing vitamin A status in a community. Thesegroups can cooperate in dark adaptometryand this is the method of choice.

Clinical dark adaptometers, designed foruse in hospitals, are expensive and sensitivepieces of equipment. There are simpler andmore robust forms of equipment that may bereadily transported for use in field studies. Vi-tamin A deficiency results in delay in rod ad-aptation to conditions of illumination of lowintensity, followed by reduction in thresholdsensitivity. Figure 5.1 shows the curve that isobtained on testing a normal subject. Figure

Figure 5.1. Normal curve of dark adaptation showing cone-rod transition time, cone threshold, and finalrod threshold (Hume, Krebs, 1949). Log millilamberts are units of intensity of illumination.


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XEROPHTHALMIA

5.2 illustrates how test curves rose progres-sively in a volunteer subject receiving a vita-min A-deficient diet.

In practice it is usually sufficient to allowboth examiner and a group of subjects fortesting to undergo dark adaptation for about30 minutes in a darkened room. At this pointmaximum rod adaptation possible will haveoccurred and the tests are carried out at thefinal rod threshold (see Figure 5.1).

Night blindness is frequently the mostprevalent form of xerophthalmia, as mightbe expected. Although serum retinol of>20 µg/dL has customarily been consideredto be “normal” it was found that about 20% ofchildren with night blindness and 10% withnight blindness and Bitot’s spot had higherlevels of serum retinol (see Table 5.4). Asmight be expected, impaired dark adaptationcould be detected with serum retinol between20 and 30 µg/dL.

Figure 5.2. Curves of dark adaptation for one deprived subject at different stages of depletion (Hume,Krebs, 1949). Log millilamberts are units of intensity of illumination, numbers on right are dates of tests.


57

Chapter 5

Conjunctival xerosis (X1A)The term conjunctival xerosis could apply toany stage of xerotic change in the conjunc-tiva (see Figure 5.3). This would range fromabnormal impression cytology, through dry-ness of the conjunctiva, to keratinization andheaping up of material as in Bitot’s spot (X1B,see below). CIC is subclinical and was dealtwith previously (see Chapter 4). In theXerophthalmia Classification (see Table 5.1)X1A distinguishes dryness from Bitot’s spot.Before this scheme was agreed upon a greatdeal of attention was given to various con-junctival appearances, including thickening,wrinkling and pigmentation. It is now recog-nized that these changes and the degree towhich they occur are not related directly tovitamin A deficiency. If the classification (seeTable 5.1) and the criteria (Table 5.2) are com-pared it will be evident that X1A is not one ofthose appearances chosen for use in surveys.This is because it has repeatedly been foundthat, while advanced instances of X1A can

be readily identified, minor changes are sub-ject to great inter- and intra-observer varia-tion. This makes X1A an unreliable indicatorof VAD. Even so it is often, wrongly, used insurveys, making interpretation of results verydifficult. To obtain reproducible and compa-rable results it is of great importance thatWHO guidelines be followed in matters likethis (WHO Expert Group, 1982).

Both experimental and clinical evidencesuggests that the process of xerosis, whichalso affects other epithelial tissues than theconjunctiva and cornea, is primarily due tochanges in the proteins of the tissue itself.Loss of tears also occurs but is a secondaryphenomenon, tending to make existing xero-sis worse. Loss of goblet cells and lack ofsecretion of mucin, is an integral, but second-ary part of the process of xerosis in the con-junctiva. Local eye infections are frequent,making the clinical condition worse, but arenot aetiologically involved.

Table 5.4. Association between xerophthalmia status and serum retinol (µg/dL) (fromSommer, West, 1996)

Clinical status Deficient Low Adequate Mean Number(<10) (10–20) (>20) of cases

XN (+), X1B (-) 27% 55% 18% 13.9 174

XN (-), X1B (+) 31% 57% 12% 13.4 51

XN (+), X1B (+) 38% 53% 9% 12.1 79

Neighbourhood – – – 17.7 282controls

Random sample 8% 37% 55% 20.0 268

XN = night blindness; X1B = Bitot’s spot; controls = neighbourhood peers of same age and sex; ran-dom sample = peers from throughout the six villages studied


58

XEROPHTHALMIA

Bitot’s spot (X1B)As was mentioned earlier, Bitot’s spot is thefinal part of the process of xerosis affectingthe bulbar conjunctiva. The typical Bitot’s spot(see Figures 5.4–5.6) occurs in the exposedpart of the conjunctiva, the interpalpebral fis-sure.

The temporal aspect is usually first affectedand consequently most Bitot’s spots are foundthere. The nasal aspect is affected later andonly in extensive involvement do the inferiorand then finally the superior quadrant undergochange. A Bitot’s spot consists of a heapingup of desquamated, keratinized epithelial cellswhich form a slightly raised area that may bereadily wiped away. This leaves an uneven,eroded base in the superficial epithelium onwhich more abnormal cells may accumulateover a few days. The transient nature of Bi-tot’s spots creates a problem over their usein surveys. A subject may “remove” a spot byvigorously rubbing their own eyelids.

Bitot’s spots vary considerably in size andshape. The areas of conjunctiva affected maybe multiple, but more usually there is a singlespot to an eye. Some single spots are ovoid,

others linear, and occasionally they take aroughly triangular form with the base close tothe limbus. None of these characteristics hasany special clinical significance (McLaren,1962).

Broadly speaking the appearance of Bitot’sspots has been likened either to 1) foam or2) cheese (see Figures 5.4 and 5.5). Gas-forming bacteria may be responsible for thefirst appearance. There is no known signifi-cance to this difference in appearance.

Undoubtedly the most significant way inwhich Bitot’s spots may be classified is as towhether they are 1) responsive to vitamin Atreatment, or 2) unresponsive (Djunaedi,Sommer, Pandji et al, 1988). There are sev-eral characteristics that may be of assistancein any attempt to identify the nature of anyBitot’s spot (see Table 5.5).

It is usually not possible to determine thecause of an unresponsive Bitot’s spot. Someappear to be stigmata of earlier deficiency andmay therefore in this sense resemble cornealscars (XS) that are considered to relate toearlier deficiency (see later). For others thereis no evidence of either earlier or presentdeficiency and these may result from localtrauma of some kind. This might be due to a

Figure 5.3. Conjunctival xerosis (X1A). Markedconjunctival thickening and wrinkling, with infil-tration and haziness of the cornea (X2). Plasmavitamin A, 3 µg/dL.

Figure 5.4. Bitot’s spot (X1B) on temporal aspectof bulbar conjunctiva in inter-palpebral fissure.Bubbles of foam are clearly visible.


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Chapter 5

Corneal xerosis (X2)Many instances of conjunctival xerosis areaccompanied by a superficial punctatekeratopathy (SPK), which can be seen whenexamined with the slit-lamp microscope(Sommer, Emran, Tamba, 1979). This sug-gests that the process of xerosis tends tospread from the conjunctiva to later involvethe cornea. Clinically evident corneal xerosis(X2) in which the cornea has a distinct hazyappearance (see Figure 5.7) tends to last fora matter of only a day or two before advanc-ing to deformation of the cornea; known askeratomalacia (see below).

combination of environmental factors amongwhich might be included ultra-violet exposureat high altitude, smoke-filled huts, or chroniceye infections, especially trachoma. This hy-pothesis is supported by the fact that Bitot’sspots form most readily on the most exposedpart of the conjunctiva. Further evidence fora role of exposure in Bitot’s spot formationare reports of their presence on unusual as-pects of the conjunctiva as a result of distor-tions of the eyelids (McLaren, 1980) (seeFigure 5.6).

Table 5.5. Characteristics of vitamin A-re-sponsive and unresponsive Bitot’s spots(X1B)

Responsive• Subject usually a child of less than 6 years

of age• With the maximum vitamin A dosage, re-

sponse usually evident within one week• Usually accompanied by generalized con-

junctival xerosis and night blindness• Males more commonly affected than fe-

males

Unresponsive• Commonly occur in children over 6 years

and in otherwise healthy adults• Usually a small, single spot• No accompanying evidence of VAD• Largely responsible for the apparent in-

crease of X1B prevalence with increasingage

Figure 5.6. A single Bitot’s spot associated withabnormal exposure of the conjunctiva due to ec-tropion associated with scar on cheek.

Figure 5.5. Bitot’s spot without foam and of a“cheesy” appearance. The nature of the materialis not known to have any significance.


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XEROPHTHALMIA

Up to the stage of corneal xerosis (X2)prompt treatment with large doses of vitaminA can result in full preservation of sight with-out any residual impairment. It is of paramountimportance that all stages of xerophthalmiashould receive the maximum treatment withvitamin A (see Chapter 11). In contrast to thelengthy full response to vitamin A therapy ofabnormal conjunctival cytology mentionedearlier (see p 44), clinical improvement hasbeen reported to take place in 70% of cor-neal lesions (X2/X3) within four days, in 95%within one week and the vast majority wereentirely healed within two weeks (Sommer,West, 1996, p 285). Histological and clinicalhealing are both subjective and clearly notstrictly comparable.

Figure 5.7. Bilateral haziness of the cornea (X2)in a young child identified in a survey.

Keratomalacia (X3A, X3B)In the 1982 WHO Xerophthalmia Classifica-tion keratomalacia has been divided into twostages according to the extent of the involve-ment of the cornea (see Table 5.1). Keratoma-lacia is characterized by softening of the cor-

neal substance in addition to increasing xero-sis of the epithelium (see Figures 5.8 and 5.9).

Corneal softening is due to a unique patho-logical process termed colliquative necrosis.The stroma becomes oedematous. It is sus-pected that activation of collagenases andother enzymes may be responsible but theprecise pathogenesis is not known.

Many years ago (Pillat, 1929) cases ofkeratomalacia in adults in China were alsodescribed as having similar colliquativechanges in the skin. This was termed“dermomalacia”. Figure 5.9 shows one eyeand the surrounding skin of a five-month-oldPalestinian refugee child who died shortlyafter admission to hospital in Amman,Jordan.There is advanced keratomalacia withalmost the entire cornea affected and thecentral area about to prolapse. In addition,the skin has a markedly burnished appear-ance which also affected much of the skin ofthe head and neck. The skin change is veryreminiscent of that described earlier asdermomalacia. As a result of this process inthe cornea there will always be some degreeof residual damage and deformity.

In corneal ulceration there is usually onlyone ulcer per eye. The typical ulcer is infero-nasal in position, about 0–2 mm in diameterand 0.25 – 0.5 mm in thickness. In about 20%of cases both eyes are affected and the char-acteristics tend to be similar. Hypopyon (col-lection of sterile pus in the anterior chamber)is common and infection is frequent.

Corneal scar (XS) – vitaminA-related

Scarring of the cornea may result from a widevariety of diseases affecting the eye. Visualimpairment is inevitable; its degree dependson the location and the density of the scar.Damage that is confined to the cornea may


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Chapter 5

be overcome by surgery. This is not possiblewhen internal structures are also involved,usually as a result of accompanying infection.Prevention is clearly infinitely preferable.Careful and detailed history taking and gen-eral physical examination, in addition to theeye examination, are of particular importancein this instance (see Figure 5.10). If, as a re-sult of these, there is any residual doubt aboutthe likely aetiology of a corneal scar, then itshould not be attributed to vitamin A defi-ciency. Table 5.6 gives the information to beelicited in order to come to a diagnosis.

Figure 5.9. Entire cornea is undergoing liquefac-tion (X3B). Skin surrounding the eye shows hy-perkeratinization suggestive of “dermomalacia”(see text).

Figure 5.10. Bilateral corneal scars (leucomata XS)in an anaemic and generally malnourished infant.The inferior situation of the scars is typical.

Figure 5.8. Colliquative necrosis (keratomalacia)affecting the greater part of the cornea (X3B).Therelative sparing of the superior aspect is typical.Plasma vitamin A, 4 µg/dL.


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XEROPHTHALMIA

Xerophthalmic fundus (XF)This rare condition has been described mainlyin school age children or young adults in southeast Asia (Teng-Khoen-Hing, 1959; Sommer,Sugana, Djunaedi et al, 1978). It appears toresult from prolonged deficiency of vitamin Ain which impairment of rod function is suc-ceeded by structural damage to the retina.Recently a report from Malawi associated the

Table 5.6. Distinguishing characteristics ofvitamin A-related corneal scars (XS)

Eye examination• Location: typically nasal and inferior on the

cornea if only a small part involved• Often bilateral, not necessarily equal in ex-

tent

History• Onset between about 2 months and 5 years• Accompanied at that time by severe PEM,

measles, severe diarrhoea, respiratory in-fection

• Absence of trauma, or prolonged purulentdischarge

whitening of the retina described in childrenwith cerebral malaria with low vitamin A sta-tus and abnormal CIC (Lewallen, Taylor,Molyneux et al, 1998). Retinal changes andsigns of raised intracranial pressure respon-sive to vitamin A were reported in a case ofsecondary VAD in the United States(Panozzo, Babighian, Bonora, 1998).

RemarksIn conclusion, there are several generalpoints that should be noted. Signs of xeroph-thalmia are usually present in both eyes, butnot necessarily to the same degree.Keratomalacia may proceed very rapidly, no-ticeably within a matter of some hours ratherthan days. This is especially true in veryyoung children. In this age group keratoma-lacia may present without any evidence ofxerosis in the conjunctiva or cornea. It fol-lows that a diagnosis of vitamin A deficiencymay be made in the absence of xeroticchanges. In corneal involvement accompa-nying infection is probably the rule. Fre-quently this obscures the classical pictureof changes due to xerophthalmia. Unless thisis remembered the result may beunderdiagnosis of xerophthalmia.


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Chapter 6

MORTALITY AND MORBIDITY

IntroductionIt can be instructive, on occasion, to look backin time and speculate about the reasons whyevents in history took the path they did. InChapter 5 it was pointed out that recognitionof xerophthalmia as a vitamin deficiency dis-ease lagged behind that of several other dis-eases of nutritional aetiology. In the presentcontext it is a cause of surprise that wide-spread acceptance of the significant impactof vitamin A on mortality and morbidity hascome only in recent years (Semba, 1999). Notlong after the discovery of fat-soluble A thevitamin was dubbed “the anti-infective vita-min” (Green, Mellanby, 1928). This was onthe basis of the susceptibility of experimentalanimals fed on diets deficient in the vitaminto infections resulting in death and of the re-sponse of humans with infections to vitamin A.

Sommer and West (1996, pp 19-61) haverecently reviewed hospital-based reports ofchildren with xerophthalmia and severe PEMin whom mortality was significantly increasedby the presence of eye signs accompanyinggeneral malnutrition. In some of these stud-ies there was a four-fold (McLaren, Shirajian,Tchalian et al, 1965) or even greater mortal-ity in children severely vitamin A deficient ascompared with those equally generally mal-nourished but with normal eyes. The implica-tions of these findings were not pursued fur-ther at that time. In explanation it should bepointed out that epidemiological and statisti-cal methodologies had not advanced suffi-

ciently in those times and there was still greatreticence on the part of governmental andother agencies to recognize the magnitudeand severity of VAD.

Mortality associated withnon-corneal xerophthalmia

The significance of vitamin A deficiency inchild survival in the community was first sug-gested by a study of Sommer, Hussaini,Tarwotjo et al (1983) that followed a point-prevalence survey of vitamin A deficiency inIndonesia (see Chapter 8). The results, pre-sented in Table 6.1, show a significantly in-creased relative risk of death in those groupswith evidence of xerophthalmia. The great-est risk is among those with both X1B andXN. It should be noted that only those withthe milder, non-corneal signs of xerophthal-mia were included.

It is probable that the mechanism of thegreater mortality in those children who hadclinical VAD was in some way related to animpairment in their immune response to anaccompanying infectious disease. Whilst it isrelatively easy to ensure that all deaths arerecorded in a study like this, it is much moredifficult to obtain accurate information as tothe cause or causes of death. In addition, inthe circumstances that prevail in field studiesit is usually not possible to make a definitivediagnosis of any accompanying infections.These matters are further discussed later


64


Table 6.1. Mortality in relation to xerophthalmia (vitamin A) status (Sommer, Hussaini,Tarwotjo et al, 1983)

Ocular status Child intervals* Deaths Mortality Relative risk(per 1000)

Normal 19,889 108 5.4 1.0

XN (+), X1B (-) 547 8 14.6 2.7

XN (-), X1B (+) 269 6 35.5 6.6

XN (+), X1B (+) 215 10 46.5 8.6

* Examined at six three-monthly intervals

when the relationship between vitamin A de-ficiency and morbidity is considered.

Vitamin A intervention andmortality in young children

The first of these trials was carried out in Aceh,Indonesia ( Sommer, Tarwotjo, Djunaedi etal, 1986). A large dose of vitamin A (200,000IU) was given every 6 months. The initial re-port found a 34% reduction in mortality in thetreated group. Alternative analyses suggestedat least 40% to >50% reduction (Tarwotjo,Sommer, West et al, 1987; West, Pokhrel,Katz et al, 1991). Figure 6.1 shows some ofthe results from this study.

Over a period of several years further fieldtrials were carried out in other locations. Asummary of these major community mortalityprevention trials is given in Table 6.2.

As an indication of the magnitude of trialsof this nature it should be noted that morethan 150,000 preschool age children took partin the eight trials described in outline above.All or some of them have formed the basis ofseveral meta-analyses that have been made.The results of all the meta-analyses are in

general agreement that improvement in thevitamin A status of deficient populations re-duces significantly the overall preschool-agechild mortality. Figure 6.2 is a summary of theresults of one of these meta-analyses of theeight major mortality intervention trials(Beaton, Martorell, Aronson et al, 1993). Theoverall reduction of mortality from this was23%.

These results are remarkably consistent inview of the fact that the communities studiedwere very heterogeneous with regard to manyfactors such as culture, ecology, disease pat-terns, and details of the interventions carriedout differed considerably.

It should also be noted that there are sev-eral reasons why the reported reductions inmortality may have underestimated the ac-tual reductions. Some deaths may have beenincluded that occurred before the vitamin Aintervention had had a chance to act. In moststudies children with xerophthalmia wereidentified, treated and excluded from the mainstudy. In the absence of the intervention thesechildren would be expected to be among themost vulnerable. Periodic large-dose vitaminA supplementation may not be the optimalmeans of improving vitamin A status in the

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Chapter 6

Figure 6.1. Cumulative mortality, by sex, of preschool-age children in Aceh, Indonesia,from Sommer, Tarwotjo, Djunaedi et al,1986.

long term. Consistent with this may be thehighest reductions in mortality being reportedfrom Bogor, Indonesia, and Tamil Nadu, In-dia (see Table 6.2), where vitamin A was pro-vided in a more physiological way. Finally,each of the eight studies reported what istermed an “intention-to-treat” analysis. In thisit is assumed that a full intervention was re-ceived by each subject supposed to do so. Ithas been found (Tarwotjo, Sommer, West etal, 1987) that in most health interventions ofthis kind those who fail to participate, termed“noncompliers”, are usually those most inneed of the intervention. Their mortality hasbeen found to be greater than that of the con-trol group (see Figure 6.3).

Knowledge of the level of noncompliancein any study is essential for assessing impact.It is also a reminder that when any measureis adopted for routine application there willalways be those who for various reasons fail

to participate. Furthermore, they are likely tobe the most at risk.

In a reassessment of most of these studiesSommer and West (1996, pp 34-37) foundthat in children aged 6 months and older thereduction in mortality tended to increase inmagnitude with age. The majority of deathsoccurred in children < 2 years of age. Theseauthors also discuss the evidence for the ef-fect on mortality of vitamin A dosing in chil-dren under the age of 6 months. Under theage of 3 months 100,000 IU appeared to havea detrimental effect, but 50,000 IU was ben-eficial. In infants over the age of 3 monthsthe larger dose was effective. 300,000 IU ina single maternal dose has been shown toraise maternal stores, vitamin A levels inbreast milk, serum retinol of breast-fed chil-dren, and to reduce mortality in infants byabout 30% (de Francisco, Yasui, Chakraborty,1994).


66


Table 6.2. Major community mortality prevention trials (Sommer, West, 1996, p 28)

Reportedmortality Primary

Study Country Vitamin A supplement reduction reference

Aceh Indonesia Large dose every 6 mo 34% Sommer et al,1986

Bogor Indonesia Vitamin A-fortified MSG 45% Muhilal et al,1988

NNIPS Nepal Large dose every 4 mo 30% West et al,1991

Jumla Nepal One large-dose follow-up 29% Daulaire et al,1992at 5 mo

Tamil Nadu India Weekly RDA1 54% Rahmathullahet al,1990

Hyderabad India Large dose every 6 mo 6% (ns*) Vijayaraghavanet al,1990

Khartoum Sudan Large dose every 6 mo +6% (ns*) Herrera et al,1992

VAST Ghana Large dose every 4 mo 19% Ghana VASTStudy Team, 1993

* Not statistically significant1 Once a week a dose was given, providing the RDA

Cause-specific mortalityThis was studied in four of the eight interven-tions subject to meta-analysis and the resultsin Table 6.3 indicate that vitamin A interven-tion tends to make more of an impact on mea-sles and diarrhoea than it does on respira-tory infections in this regard.

It should be noted that this seems to beconsistent with the results of studies that haveattempted to investigate the impact of vita-min A intervention on several aspects of theevolution of various infectious diseases (seesection on morbidity later).

Contribution of vitamin Adeficiency to child mortality

While subclinical vitamin A deficiency is muchless fatal than overt xerophthalmia, it is verymuch more widespread (see Chapter 8).Beaton, Martorell, Aronson et al, 1993 (seeFigure 6.4), were unable to find any associa-tion in the field trials that have been citedabove between relative risk (RR) of mortalityand prevalence of xerophthalmia.

This may have been due in part to differ-ences in the reporting of xerophthalmia in the


67

Chapter 6

Figure 6.2. Meta-analysis of the eight major community mortality intervention trials. For details includ-ing explanation of fixed effect and random effects, see reference (Beaton, Martorell, Aronson et al,1993).

different studies (McLaren, 1991), but it prob-ably indicates that xerophthalmia does notmake a major contribution to mortality withina community. The largest contribution is mostlikely to be attributable to subclinical vitaminA deficiency.

In Nepal a sustained reduction in child mor-tality with vitamin A was shown for the firsttime (Pokhrel, Khatry, West et al, 1994).Where deficiency is endemic vitamin A sup-plementation can achieve a rapid reductionin early childhood mortality and a lower levelof mortality can be sustained as long as cap-sule coverage is adequate (>85%).

In Malawi 377 HIV-negative women hadserum retinol mesured in the second and thirdtrimester of pregnancy. Their infants wereobserved from delivery until 12 months of age.Mothers whose infants died had serum reti-nol levels lower than mothers of the survivors.Infants born to mothers whose serum retinolswere in the lowest quartile had a three-foldgreater mortality risk than those of motherswith serum retinols in the higher quartiles(Semba, Miotti, Chiphangwi et al, 1998).

It has been estimated (Humphrey, West,Sommer, 1992) that worldwide vitamin A de-ficiency may be responsible for as many as


68


Table 6.3. Cause-specific mortality, vitamin A supplementation community preventiontrials (Sommer, West, 1996, p 41)

Symptoms/Diseases

Measles Diarrhoea RespiratoryStudyc Vitamin A Control Vitamin A Control Vitamin A Control

Tamil NaduDeaths (n) 7 12 16 33 2 3RRa 0.58 0.48 0.67

NNIPSDeaths (n) 3 12 39 62 36 27RR 0.24 0.61 1.29/1.00b

JumlaDeaths (n) 3 4 94 129 18 17RR 0.67 0.65 0.95

Ghana VASTDeaths (n) 61 72 69 111 47 45RR 0.82 0.66 1.00

a RR (Relative Risk): Cause-specific mortality rate of vitamin A group divided by rate in control groupb Originally published results RR=1.29; reanalysis as an associated cause that recognizes other un-

derlying causes RR=1.00c For details see Table 6.2

Figure 6.3. Mortality in the Aceh trial among children in treatment villages who did and did not receivetheir intended vitamin A dose, compared with children in control villages. Mortality was higher amongchildren who were assigned to receive vitamin A but did not get it than for any other group, includingchildren in control villages (Tarwotjo, Sommer, West et al, 1987).


69

Chapter 6

1.3 to 2.5 million deaths annually. In addition,PEM is considered to be a contributory causeof infant and child deaths in nearly 50%(Puffer, Serrano, 1973). Recently much atten-tion has been given to the importance in in-fections of other micronutrient deficiencies,especially of zinc (see Chapter 7).

Measles mortality and vitamin Atreatment

Measles occupies a unique position amongcommon childhood infectious diseases andvitamin A deficiency. Of these diseases, it isin measles alone that the infective agent, inthis case a virus, invades the eye. In seriouscases it causes a damaging measles kerato-conjunctivitis. Even immunization againstmeasles has been shown to result insymptomless, minimal invasion of the cornea

which may take months to disappear. This eyepathology may predispose to corneal lique-faction in the presence of vitamin A deficiency.

Measles generally takes a more seriousform in the generally undernourished child,resulting in more frequent and more seriouscomplications and a much higher death ratethan in the well-nourished. This was shownin the community prevention trials referred toalready (see Table 6.3). Table 6.4 shows thatin hospital the majority of deaths occur in chil-dren under the age of 2 years.

Dramatic reduction in mortality rates in hos-pitalized cases of measles has been repeat-edly shown in those where treatment includedvitamin A supplementation (see Figure 6.5).

1.2

1

0.8

0.6

0.4

0.2

0

Relative Risk (RR)

0 2 4 6 8 10 12 14Prevalence of xerophthalmia (%)

Ghana

MSG

Aceh

Sarlahi

Sudan

Hyderabad

Tamil Nadu

Jumla

Figure 6.4. Relative risk of mortality and prevalence of xerophthalmia. No relation-ship could be established (Beaton, Martorell, Aronson et al, 1993).


70


Figure 6.5. Measles case-fatality rates among hospitalized patients randomized to receivehigh-dose vitamin A (cod liver oil in the London trial) compared with those of their controls.Vitamin A supplementation reduced mortality by 50% in all three trials (Sommer, West,1996, p 53).

Table 6.4. Measles mortality – Cape Town Trial (Hussey, Klein, 1990)

Vitamin A Controls RelativeRisk

Age Children Deaths Mortality Children Deaths Mortality Control:(months) (%) (%) Vitamin A

<6 4 0 – 3 1 33.3 33 : 06–12 53 1 1.9 64 7 10.9 5.7 : 1

13–23 19 1 5.3 18 1 5.6 1.1 : 1

0–23 76 2 2.6 85 9 10.6 4.1 : 1

≥24 16 0 – 12 1 8.3 8.3 : 0

Total 92 2 2.2 97 10 10.3 4.7 : 1


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Chapter 6

Vitamin A supplementationand maternal mortality

The preliminary results of the first trial of thiskind caused a considerable stir when theywere reported at the XVIII IVACG Meeting inCairo, 22–26 September 1997 (West, Khatry,Katz et al, 1997). The definitive paper waspublished nearly 18 months later (West, Katz,Khatry et al, 1999) together with an editorial(Olsen, 1999). An area of Nepal was chosenfor the study where VAD is known to be com-mon in pregnant women as well as in youngchildren. Well over 40,000 women partici-pated and were observed over 31/2 years. Ap-proximately equal numbers in three matchedgroups received vitamin A (7,000 µg retinolequivalents on a weekly basis), β-carotene(42 mg or 7,000 RE on a weekly basis), or aplacebo). Maternal deaths from any causeduring pregnancy or within 12 weeks of de-livery were the end point. The preventive ef-fects, expressed as relative risks were 0.60(40% reduction) for vitamin A and 0.51 (49%reduction) for β-carotene (see Table 6.5). It issuggested that the antioxidant effect of β-carotene might have had some relationshipto the higher reduction rate rather than that

of vitamin A. There was no reduction in fetalor infant mortality through until 6 months ofage nor any impact on neonatal birth weight.

It is understood that similar trials are beingconducted in other areas but results are notyet available. A preliminary report at the XIXIVACG Meeting in March 1999 (Hakimi,Dibley, Suryono et al, 1999) on a trial withvitamin A and zinc supplements on maternalpostpartum infections showed that there wassignificant benefit in groups receiving vitaminA but zinc gave no improvement. There is nodoubt that if the results from Nepal are con-firmed from elsewhere there could be a sig-nificant extension of the public health impor-tance of vitamin A intervention into the areaof maternal health where the mortality rate indeveloping countries far exceeds that in thedeveloped countries.

Vitamin A supplementationand infectious morbidity

Mortality and morbidity are related but clearlyquite distinct. All disease states carry someelement of morbidity. In a medical context theword relates in an unspecific way to illness.

Table 6.5. Impact of supplementation on mortality related to pregnancy up to 12 weekspost partum (West, Katz, Khatry et al, 1999)

Placebo Vitamin A β-carotene Vitamin A orβ-carotene

Number of pregnancies* 7,241 7,747 7,201 14,948Number of deaths 51 33 26 59Mortality (per 100,000 704 426 361 395pregnancies)Relative risk (95% CI) 1.0 0.60 (0.37–0.97) 0.51 (0.30–0.86) 0.56 (0.37–0.84)p value <0.04 <0.01 <0.005

* Includes 157 pregnancies that were lost to follow up (43, 70, and 44 in the placebo, vitamin A, andβ-carotene groups, respectively)


72


Some instances of morbidity may result indeath, but that aspect is normally dealt withseparately. Fatal diseases have, until recently,been given more attention than the muchmore numerous non-fatal ones. This may bepartly because the latter have been consid-ered to be of only secondary importance. Itmay also be because they are much moredifficult to document. A fatality is a discrete,one-off event; a morbidity or disability is quitevague. Morbidity may be acute or chronic,mild or severe.

The relationship of morbidity due to VADand infection is complicated by several fur-ther points. There is an apparent synergisticrelationship between impaired vitamin A sta-tus and infections; each seems to increasethe risk of the other (see also Chapter 9).Other nutritional deficiencies, especially PEMof mild degree, are often also present and thismakes interpretation of results difficult. Epi-sodes of infectious diseases vary greatly fromcase to case and may also differ to a consid-erable extent from one location to another.For many reasons their recognition in differentstudies may be based upon very different crite-ria. Finally, although the phenomenon has beennoted for many years, it is only relatively recentlythat research workers have given due regardto the fact that the acute-phase reaction asso-ciated with infections also causes a depressionof serum retinol. This casts doubt on the valueof serum retinol as an indicator of vitamin A sta-tus under such circumstances. This subject willbe considered in more detail in Chapter 9.

Vitamin A deficiency has been induced inexperimental animals for many decades. Theuniform experience has been that this nutri-tional deficiency, more than any other, is as-sociated from a relatively early stage with thedevelopment of infections, especially thoseaffecting epithelial tissues. Most prominenthave been those of the upper and lower res-piratory tracts, parts of the gut, and the genito-urinary tract (Moore, 1957). These infections

often became apparent early on in the defi-ciency, long before the changes of xeroph-thalmia occurred (McLaren, 1959).

Diarrhoeal diseases

This is probably a less-well defined group ofdiseases than the others to be consideredhere. There is a variety of bacterial and viralorganisms that have been isolated from pa-tients with diarrhoea. Isolation does not nec-essarily mean that an organism was respon-sible for the diarrhoea. In addition, even withfull laboratory facilities, in some instances noorganisms have been isolated. Furthermore,the difficulties of defining what constitutes acase are probably greater for diarrhoea thanfor any other infection or group of infections.

Cross-sectional studies of impaired vitaminA status and various infections have beencarried out in many developing countries(Sommer, West, 1996, pp 62-98). The strong-est association in most was with diarrhoea,especially when it was persistent, chronic, orsevere. From these studies the relationshipis not clear. Which came first?

Intervention trials cast some light on thislast point. Vitamin A supplementation appearsnot to have an effect on mild diarrhoea (usu-ally defined as 3 or 4 stools/day). As wasnoted earlier, it does reduce diarrhoea-relateddeaths. As expected then, it also reduces theincidence of severe diarrhoea and the ben-efit is proportional to the number of stools/day (see Table 6.5).

Respiratory diseases

This term usually applies to diseases affect-ing the lower respiratory tract; in general thismeans one form or another of bronchitis orpneumonia. Fever, cough, rhonchi or rales(sounds detected by stethoscope) are cus-tomarily required to be present for the diag-nosis to be made.


73

Chapter 6

Table 6.6. Diarrhoeal episodes by fre-quency of movements (Brazil) (Barreto,Santos, Assis et al, 1994)

Number of loose Relative Riskmovements (Vitamin A group)

3 0.924 0.90*5 0.80**6 0.77**

* p < 0.05, ** p < 0.01

Figure 6.6. The prevalence of respiratory disease among Indonesian children presenting to the CicendoEye Hospital increased with the severity of their xerophthalmia (p <0.01 for linear trend) (Sommer, 1982).

Animal studies, clinical and autopsy stud-ies in children, and observational studies inhuman populations all show an associationbetween vitamin A deficiency and respiratoryinfections. Respiratory disease prevalence

increased in a linear fashion with increasingseverity of xerophthalmia in a large hospitalstudy (see Figure 6.6).

However, meta-analysis from mortality andmorbidity intervention trials showed in gen-eral a lack of any impact of vitamin A sup-plementation on acute lower respiratory tractinfections (ALRIs). There was some indica-tion that there might be reduction in the se-verity, if not the duration, of respiratory symp-toms. It has been pointed out that increase incough in the supplemented group might be afavourable response (Herrera, Fawzi, Nestelet al, 1996). Strength of the cough reflex couldbe beneficial in removing infective material.These conclusions have been supported ingeneral by subsequent studies from other


74


countries. Treatment with vitamin A of respi-ratory syncitial virus (RSV) infection also hadno significant benefit (Dowell, Papic, Breseeet al, 1996).

Measles

The evidence for the association between vi-tamin A deficiency and measles, in its vari-ous aspects (see Chapters 6 and 9), isstronger than for any other infectious disease.Diagnosis probably has a firmer basis, as asingle organism is responsible and the clini-cal picture is usually typical. Measles is theonly specific disease for which there is firmevidence that vitamin A status influences mor-bidity and mortality (Sommer, West, 1996, pp62-98).

Hospital-based studies in South Africa dem-onstrated that both the complications (seeTable 6.7) and outcome (see Table 6.8) inmeasles are significantly improved by vitaminA supplementation.

Outcome during the prolonged recoveryafter discharge home is also markedly im-proved by a further dose of vitamin A (seeTable 6.9).

Both measles and vitamin A deficiency areknown to impair immune response and thiscombination helps to explain the serious na-ture of the disease in most developing coun-tries. With the widespread take-up of mea-sles immunization as part of the WHO Ex-panded Programme on Immunization (EPI)there is already evidence of a marked fall incorneal blindness associated with measles(Foster, Yorston, 1992). The combination ofvitamin A supplementation with measles im-munization is discussed later (see Chapter11).

Recent work suggests that a single doseof 200,000 IU (210 µmol) retinol does not en-hance the immune response (Rosales,Kjolhede, 1994) nor is it effective in reducingmeasles complications (Rosales, Kjolhede,

Tables 6.7. Measles complications – Cape Town vitamin A controlled treatment trial(Hussey, Klein, 1990)

Complication Vitamin A Controls Relative RiskN=92 N=97 Vitamin A : Controls

Pneumonia ≥10 days 12 29 0.44 (0.24, 0.80)

Diarrhoea ≤10 days 8 21 0.40 (0.19, 0.86)

Post-measles croup 13 27 0.51 (0.28, 0.92)

Requiring airway 3 9 0.35 (0.10, 1.26)

Herpes stomatitis 2 9 0.23 (0.05, 1.06)

Intensive care 4 11 0.38 (0.13, 1.16)

Hospital days 10.54 15.24 p < 0.004


75

Chapter 6

Table 6.9. Post-hospital outcome – Durban measles vitamin A controlled treatment trial(Coutsoudis, Broughton, Coovadia, 1991; Coutsoudis, Kiepiela, Coovadia et al, 1992)

6 Weeks 6 MonthsVitamin A Placebo Vitamin A Placebo

(N = 24) (N = 24) (N = 20) (N = 16)

Weight gain (kg) 1.29 ± 0.17 0.90 ± 0.14 2.89 ± 0.23 2.37 ± 0.20

Diarrhoea episodes 6 12 3 6

Score/episode – diarrhoea 2.17 ± 0.31 2.25 ± 0.25 1.67 ± 0.67 2.17 ± 0.31

URI* episodes 7 9 3 8

Score/episode – URI 1.71 ± 0.28 2.66 ± 0.17 2.00 ± 0.58 2.37 ± 0.18

Pneumonia episodes 5 6 0 3

Score/episode – pneumonia 4.40 ± 0.98 6.67 ± 0.67 − 6.67 ± 0.67

Chest x-ray score ≥3 2 6 0 3

IMS 2.21 ± 0.45 5.74 ± 1.17 0.60 ± 0.22 4.12 ± 1.13

* Upper Respiratory Infections

Table 6.8. Hospital outcome – Durban measles vitamin A controlled treatment trial(Coutsoudis, Broughton, Coovadia, 1991; Coutsoudis, Kiepiela, Coovadia et al, 1992)

Vitamin A PlaceboOutcome (N = 29) (N = 31)

Duration (days) – pneumonia 3.8 ± 0.4 5.7 ± 0.8

Duration (days) – diarrhoea 3.2 ± 0.7 4.5 ± 0.4

Duration (days) – fever 3.6 ± 0.3 4.2 ± 0.5

Clinical recovery in <8 days 28 (96%) 20 (65%)

IMS on day 8* 0.24 ± 0.15 1.37 ± 0.40

* lntegrated Morbidity Score


76


Goodman, 1996) and doubling the dose maybe required. Where access to healthcare andimmuninization is good and where VAD is mildto moderate vitamin A supplementation mayhave no effect on general morbidity(Ramakrishnan, Latham, Abel et al, 1995).High-dose treatment (one dose of 200,000 IUvitamin A) did not improve morbidity in hospi-talized, malnourished children in Congo, butdaily low dosage (5,000 IU) reduced the inci-dence of diarrhoeal disease but had no ef-fect on acute lower respiratory infections(Donnen, Dramaix, Brasseur et al, 1998). Inone study in Indonesia (Humphrey, Agoestina,Wu et al, 1996) neonatal vitamin A supple-mentation reduced infant mortality and theprevalence of severe respiratory infectionamong young infants.

HIV/AIDS

Evidence is accumulating that vitamin A sta-tus in HIV infection is of considerable impor-tance. Serum retinol levels are depressed andin proportion to the severity of infection(Beach, Mantero-Atienza, Shor-Posner et al,1992). Mortality in AIDS patients is higher inthose with lower serum retinol levels (Tang,Graham, Kirby et al, 1993). Vitamin A sup-plementation of a group of HIV-positive injec-tion drug users had no significant effect onHIV load or CD4 lymphocyte count (Semba,Caiaffa, Graham et al, 1995).

It was at first reported that mothers with HIVinfection have an increased chance of pass-ing on the infection to their offspring if theirserum retinol is low (Semba, Miotti, Chiph-angwi et al, 1994). However, this has not beensubsequently confirmed by three recentlycompleted controlled trials of vitamin A sup-plementation of HIV-positive pregnantwomen. No significant differences were foundin mother-to-child-transmission between con-trol and supplemented groups (Humphrey,2000; Blaner, Gamble, Burger et al, 1997).One study was unable to show any benefi-

cial effects of vitamin A supplementation onpregnancy outcomes and T-cell counts in HIV-infected women, although these occurred withmultivitamins (Fawzi, Msamanga, Spiegel-man et al, 1998). Maternal vitamin A defi-ciency during HIV infection is reported to pre-dispose to growth failure (Semba, Miotti,Chiphangwi et al, 1997) and to increased in-fant mortality (Semba, Miotti, Chiphangwi etal, 1995). Vitamin A supplementation of HIV-infected infants significantly reduced morbid-ity (Coutsoudis, Bobat, Coovadia et al, 1994)and reduced mortality among both HIV-in-fected and non-infected malnourished chil-dren (Fawzi, Mbise, Hertzmark et al, 1999).

An interesting study was carried out inMombasa, Kenya (Mostad, Overbaugh,DeVange et al, 1997), on factors that affectHIV-1 shedding in cervical and vaginal se-cretions. Both hormonal contraceptive useand vitamin A deficiency were associatedwith increased risk of vaginal shedding. Af-ter adjustment for CD4 count severe VADmoderate VAD and low normal vitamin Astatus were associated with 12.9, 8.0, and4.9-fold increased risk of vaginal shedding,respectively. The public health implicationsof these results in the control of HIV/AIDSspread are evident.

Malaria

In an early study no relation was found be-tween vitamin A status and malarial infection(Binka, Ross, Morris et al, 1995). A later studyin Papua New Guinea (Shankar, Genton,Semba et al, 1999) found a substantially lowerincidence of clinical episodes of falciparummalaria (p=0.001), parasite density (p=0.09),and prevalence of spleen enlargement(p=0.01) in children attending health facilities.No such effects were found in vivax infection.The role of iron and zinc supplementation inmalaria are considered in Chapter 7.


77

Chapter 6

Other infections

Urinary tract

Bacteriuria was more than fourfold greater inchildren with xerophthalmia than in those with-out and the prevalence increased with theseverity of xerophthalmia (Brown, Gaffar,Alamgir, 1979).

Otitis media

Children with abnormal CIC had a significantlygreater risk of middle ear infection in a studyin Truk (Lloyd-Puryear, Humphrey, West etal, 1989).

Meningococcal disease

Meningococcal disease is a major cause ofchild morbidity and mortality in sub-SaharanAfrica. A study in Rwanda (Semba, Bulterys,Munyeshuli et al, 1996) found a case fatalityrate of 20 %, most patients had low serum reti-nol levels, and mean CD4 lymphocyte percent-age was higher and mean CD8 lymphocytepercentage lower in children with meningitiscompared with reference populations. Vita-min A intervention appears not to have beencarried out yet.

RemarksDespite a great deal of research there is stillmuch we do not yet know about the precisecontribution that VAD makes to morbidity ininfectious diseases. This will probably remainso until we are in possession of more accu-rate methods of defining the various mani-festations of morbidity and until some exist-ing discrepancies have been resolved. Theselatter have been discussed by Kirkwood(1996). Epidemiological studies, describedhere, have indicated that vitamin A supple-mentation reduces child mortality and severemorbidity and that most of the reduction isdue to the effect on diarrhoea and measles.These studies have not shown a similar ef-fect on acute lower respiratory tract infections(ALRIs). No explanation exists at present forthis difference, especially in view of the evi-dence that supplementation with zinc benefitsboth diarrhoeal and respiratory infections (seeChapter 7). Observational studies and animalexperiments tend to show a beneficial effectof supplementation on lung disease. Moreo-ver, in clinical trials in measles much of theimpact of vitamin A on mortality and morbid-ity in measles has been related to reductionin incidence and severity of associated pneu-monia. Notwithstanding, all are agreed thatundernourished children treated for pulmo-nary infections should be given supplemen-tal vitamin A to improve their status.


79

Chapter 7

OTHER EFFECTS OF VITAMINA DEFICIENCY

Introduction

In the first edition of the Manual it was sug-gested that much of the evidence for the im-portance of VAD in this chapter was basedon work in experimental animals and lackedfirm evidence as far as human disease wasconcerned. In recent years there has been asteady increase in our knowledge of the roleof vitamin A, especially in the form of retinoicacid (see Chapter 3) in many systems of thebody. We are on ever increasingly firm groundto use the term vitamin A deficiency disorders(VADD) to cover all possible consequences ofthe lack of dietary intake of vitamin A.

Another development that has gained in-creasing momentum in recent years is theconcept that VAD should not be consideredin isolation, but recognised to occur togetherwith other nutrient deficiencies. This is, ofcourse, by no means a new concept. It haslong been accepted that almost always dietarydeficiencies are complex, involving many nu-trients to varying degree. In practical termsthis has usually come down to a small groupof nutrients. In the case of vitamin A its in-teractions with two essential elements, iron andzinc, have been highlighted in particular. Theseinteractions as they apply to our understandingof VADD are dealt with in this chapter. At thesame time this broadening concept has begunto have an influence on thinking in relation tothe control of VADD (see Chapter 11).

Growth

The first clearly evident response of a younganimal to dietary restriction of any kind is adecrease in the velocity of growth. Young ani-mals, and children, have relatively highernutritional requirements partly because theyneed nutrients for growth as well as mainte-nance. Vitamin A is no exception (see Chap-ter 3) and in fact is among the nutrients to adeficiency of which the growing organismappears to be most sensitive.

The situation in the young child is infinitelymore complicated than that in animals. It can-not be so clearly defined nor can specific re-strictions be applied as in the case of experi-mental animals. Furthermore, there are fre-quently accompanying infections and theseinfluence nutrient status in several ways.Appetite is usually impaired, pyrexia tends toincrease the demand for nutrients, and ab-sorption may be impaired by gut infestationsand infections.

Another difficulty is the multiplicity of waysin which growth is customarily assessed.Skeletal measurements, such as height andhead circumference, during undernutritionundergo decrease in the velocity of their rateof increase. There is no absolute loss.Height/age is usually employed to indicate“stunting”.


80

OTHER EFFECTS OF VITAMIN A DEFICIENCY

Figure 7.1. Children with corneal disease (X2/X3) were shorter than children who had Bitot’s spots(X1B) (p < 0.01); children with X1B were shorter than their matched controls (p < 0.01). There were nosignificant differences in height between randomly sampled children without xerophthalmia (normalrandom sample) and matched controls (Sommer, 1982).

On the other hand, measurements of softtissues like muscle and fat may involve ab-solute loss of tissue. Body weight, skinfoldthickness and muscle circumference meas-urements are of this type. Weight/height indi-cates “wasting”, a more acute state of growthretardation than “stunting”. Some of thesemeasurements are subject to quite large ob-server errors. While body weight can bemeasured with considerable accuracy, therehas to be some doubt about its interpretation,

especially in children. Body composition isknown to vary considerably in malnutrition;fat and muscle decrease but water increasesproportionately. Consequently weight may notaccurately reflect healthy body mass. Therelationship between anthropometric statusand mortality was discussed in Chapter 6.

Children with corneal xerophthalmia haveconsistently been observed to be stunted.This has perhaps best been documented in

OTHER EFFECTS OF VITAMIN A DEFICIENCYSIGHT AND LIFE MANUAL

81

Chapter 7

the country-wide survey in Indonesia carriedout in 1978–79 (Sommer, 1982) (see Figure7.1). The degree of vitamin A deficiency wasproportional to the degree of retardation ofgrowth. There is also evidence for frequentwasting in xerophthalmic children. In this moreacutely deficient state mortality may makeinterpretation difficult.

It appears that periodic large-dose vitaminA supplementation has a significant impacton growth in children with xerophthalmia, butnot on those with evidence of subclinical de-ficiency. However, three studies in which pre-formed vitamin A was consumed in adequateamounts regularly showed slight improvementin linear growth (Sommer, West, 1996, pp163-188).

Several studies of the effect of vitamin Asupplementation on growth have failed todemonstrate any effect (Ramakrishnan, La-tham, Abel, 1995a; Kirkwood, Ross, Arthur etal, 1996; Fawzi, Herrera, Willett et al, 1997).It may be pointed out that “absence of evi-dence is not evidence of absence”. This gen-eral principle in interpretation of results shouldbe applied to the negative results found inthese studies. A group in India (Bahl,Bhandari, Taneja et al, 1997) observed im-proved weight gain with vitamin A supplemen-tation only in the summer season when sub-clinical vitamin A deficiency peaks. Studies inNepal (West, Le Clerq, Shrestha et al, 1997)and Indonesia (Hadi, Stoltzfus, Dibley et al,2000) both reported improved growth withsupplemental vitamin A. The effect was seenmost in children with the lowest serum retinollevels and in the long term affected mainlyheight. Soft tissue growth improvementtended to occur earlier on.

A possible mechanism for an effect of vita-min A on growth is provided by a study car-ried out in a group of short prepubertal chil-dren (Evain-Brion, Porquet, Thérond et al,1994). Fasting plasma retinol correlated with

nocturnal growth hormone (GH) secretion butnot with stimulated GH secretion. Dietary in-take of vitamin A was lower in children withlow nocturnal GH secretion, and supplemen-tation with vitamin A for 3 months increasedtheir nocturnal GH secretion.

There is one aspect of growth and devel-opment that does not appear to have beenaddressed in relation to a possible effect ofvitamin A deficiency. That is brain growth andintellectual development.

Immune responseInterest in the possibility of vitamin A beinginvolved in the function of the immune sys-tem derived first from the association of vita-min A deficiency with infectious diseases.More recently it has been shown experimen-tally that retinoids can stimulate immune re-sponses.

There are two distinct responses to expo-sure to antigens; humoral and cellular (cell-mediated) immunity. Humoral immunity re-sults from antibody production mediated byB-lymphocytes, which is often T-lymphocyte-dependent. Cellular immunity is mediated byT-lymphocytes. There are two main effectormechanisms: cytolytic T-lymphocyte (CTL)responses, and delayed-type hypersensitiv-ity (DTH) responses.

There are also natural killer (NK) cells,which are part of the innate or nonspecificimmune system. Phagocytic cells also belongto this system.

It has been proposed (Ross, 1996) thatthere are broadly speaking two hypothesesto explain the protective action of vitamin Aagainst infection (see Table 7.1).

The epithelial cell linings of organs and tis-sues are generally considered to have a de-fensive function. They have been considered


82


Table 7.1. Two contrasting hypotheses for the protective role of vitamin A against infec-tion (after Ross, 1996).

Epithelial barrier hypothesis Immunologic response hypothesis

The basic reaction is The basic reaction isOFFENSIVE DEFENSIVE

This protects against invasion This enhances the body’sby infection defence against pathogens

Structural integrity is of Functional integrity isgreatest importance most important, as is

cell differentiation

Consequently resistance to Consequently resistanceestablishment of infection to proliferation of infectionwill be reduced by VAD will be reduced by VAD

Major effect of vitamin A Major effect of vitamin Aintervention will be intervention will bedecreased incidence of decreased duration and/orinfection severity of infection

to provide a first line of defence in resistenceto infection taking place. Ross argues that thisis a misconception and that they primarilyhave an offensive role. On the other hand theimmunologic response is a defensive re-sponse against infection once it has takenplace.

The available evidence as to which mightbe closer to reality from studies of humanpopulations is strictly limited (see Chapter 6).It would be expected that offensive protec-tion would reduce the incidence of infections.A defensive mechanism would be likely toreduce the duration or the severity of an in-fection. As was shown in Chapter 6, the fewstudies that addressed these points tendedto suggest that the impact of vitamin A

supplementation has been on duration andseverity. This supports the immunologic re-sponse hypothesis.

Most of the evidence from both animal andhuman studies suggests that the various as-pects of humoral immunity are little affectedby vitamin A deficiency. Cell-mediated immu-nity, however, has been shown to be mark-edly impaired. The production and matura-tion of lymphocytes are reduced by lack ofvitamin A. In a study in Indonesia it was foundthat the ratio of T-cells bearing CD4+ andCD8+ antigens was lower in the peripheralblood lymphocytes of xerophthalmic childrencompared with non-xerophthalmic controls(Semba, Muhilal, Ward et al, 1993). After vi-tamin A supplementation the proportion of


83

Chapter 7

CD4+ to CD8+ T-cells and the percentage ofnaive CD4+ T-lymphocytes increased.

The precise mechanisms whereby vitaminA plays a part in maintaining normal functionof the immune response are not yet fully un-derstood. The active form at the cellular levelappears to be retinoic acid, but it is possiblethat other metabolites of retinol may also beactive.

Semba (1998) has recently reviewed therole of vitamin A and related retinoids in im-mune function. Table 7.2 is a simplified ver-sion of the table in his paper.

Interaction of iron andvitamin A

It has long been known that vitamin A defi-ciency and iron deficiency tend to exist to-gether in population groups. This might beexpected to occur because natural dietarieswhen deficient usually involve more than a

single nutrient. Controlled trials have beencarried out in several countries in which vita-min A supplementation has brought about asignificant increase in haemoglobin level(Sommer, West, 1996, pp 150-162). The bestresults were obtained when daily ingestion ofvitamin A in amounts close to recommendedlevels of intake was used.

There is some evidence that administrationof iron to treat anaemia may exacerbate co-existing infection. Many pathogenic bacteriarequire iron and might proliferate as they com-pete for it. In one study (Northrop-Clewes,Paracha, McLoone et al, 1996) an increasein dietary intake of vitamin A under these cir-cumstances appeared to counteract any ad-verse effects of iron. The authors suggest thatthe beneficial effects of vitamin A on iron sta-tus may be related to reduced levels of infec-tion.

Fortification of sugar with vitamin A wasused in Guatemala to study the effect on ironstatus over a prolonged period (Sommer,West, 1996, pp 150-162). Table 7.3 showsthe mean changes sampled at 6-monthly in-tervals over a 2-year period. It was concludedthat there was initially enhanced iron mobili-zation leading to lower iron stores. This prob-ably triggered increased efficiency of ironabsorption which would gradually restore ironstores. These in turn would make availablefor haemopoiesis iron at an enhanced levelover that available before sugar fortificationbegan. It was shown recently (Garcia-Casal,Leets, Layrisse, 2000) that β-carotene im-proved the absorption of iron in vitro, and alsoof non-haem iron from rice, wheat and maizein humans (Garcia-Casal, Layrisse, Solanoet al, 1998). It was suggested that they forma complex with iron, keeping it soluble in theintestional lumen and preventing the inhibi-tory effect of phytates and polyphenols on ironabsorption.

Table 7.2 Main immune response elementsthat may be regulated by retinoids (afterSemba, 1998).

Keratinization

Mucin production

Haematopoiesis (influences many types of cell)

Apoptosis (programmed cell death)

Function of neutrophil, natural killer, mono-cyte/macrophage, various lymphocyte andother cells

Immunoglobulin production

Production of numerous interleukins


84


Figure 7.2. Relationship between haemoglobin level and prevalence of vitamin A deficiency assessedby conjunctival impression cytology (CIC) in children 3–6 years of age in Truk, Micronesia (Lloyd-Puryear, Mahoney, Humphrey et al, 1991).

Table 7.3. Change in serum retinol and iron status in preschool children following sugarfortification with vitamin A in Guatemala (Mejia, Arroyave, 1982)

Duration of study (months)

6 12 18 24

No. of subjects analized 77 75 46 51

Retinol (µg/dL) +5.1* +5.2* +3.6* +2.5

Serum iron (µg/dL) +4.5* -3.6 +13.1* + 9.1*

Total iron-binding capacity (µg/dL) +18.3* -8.8 -7.8 -13.6

Transferrin saturation (%) +0.6 -1.0 +3.8* + 2.2*

Serum ferritin (ng/ml) -3.3* +2.1 +5.5* + 4.9*

* p ≤ 0.05


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Chapter 7

The prevalence of anaemia associated withvitamin A deficiency has not been estimated.It is likely to be quite widespread. Iron defi-ciency affects hundreds of millions of theworld’s population. Especially vulnerablegroups are young children and women in thereproductive age period. These groups arealso at risk of vitamin A deficiency. One re-cent study in the Pacific region (Lloyd-Puryear, Humphrey, West, 1989) showed thatthe prevalence of subclinical vitamin A defi-ciency, as evidenced by abnormal CIC, wasinversely proportional to the haemoglobinlevel (see Figure 7.2).

The mechanism of vitamin A-related anae-mia is unclear. It has consistently beenshown that vitamin A deficiency restricts therelease of iron from the depots, resulting inevidence of iron overload and, in the ab-sence of increased absorption of iron, even-tually in anaemia. Although infection alsocauses iron overload, it can occur in the ab-sence of infection.

Serum iron tends to be low and vitamin Asupplementation causes increase in serumiron and in % transferrin saturation (Sommer,West, 1996, pp 150-162). Recent animal work(Rosales, Jang, Pinero et al, 2000) showedthat a fall in haemoglobin due to feeding low-iron diets was accompanied by a lowering ofplasma retinol but an increase in hepaticretinyl esters. Low iron status seems to inter-fere with hepatic release of vitamin A.

In conclusion, despite the need for moredetailed understanding of vitamin A–iron in-terrelationships, the prevention of vitamin Adeficiency should be considered along withiron supplementation in the control of nutri-tional anaemia (IVACG, 1998).

Interaction of zinc andvitamin A

This relationship has been known for sometime but has only recently begun to be ex-plored in the context of VADD. Many enzymesare zinc-dependent and among them is reti-nol dehydrogenase involved in rod function.As a result it has been found that some casesof night blindness that are resistant to vita-min A may respond to zinc. Zinc deficiencymay interfere with the synthesis of retinol-binding protein.

A number of recent studies have demon-strated that supplementation with zinc has abeneficial effect in diarrhoeal and some otherinfectious diseases (Bhutta, Black, Brown etal, 1999; Shankar, 1999) very similar to thatof vitamin A. One preliminary report (IVACG,1999) found a significant increase in mortal-ity in a group of children receiving a large doseof zinc. These trials are at an early stage andsafety issues and problems with assessmentof zinc status have still to be resolved. Com-bined therapy with vitamin A and zinc doesnot appear to have been reported until thepresent.

This area is tending to become complicatedby the use of supplementation with varyingcombinations of the three micronutrientsvitamin A, iron and zinc. Lymphocyte respon-siveness has been enhanced with vitamin Aand zinc (Kramer, Udomkesmalee, Dhana-mitta et al, 1993). Growth in height andweight was improved by vitamin A but not byzinc (Smith, Makdani, Hegar et al, 1999). Aninteresting report claimed a better haem-atologic response in anaemic women whenvitamin A and zinc were added to iron thanwhen treatment was with iron alone orvitamin A and iron (Kolsteren, Rahman,Hildebrand et al, 1999).Recently it wasshown that supplementation with iron and


86


zinc improved serum retinol levels (Muñoz,Rosado, López et al, 2000). It seems likelythat there will be many more studies likethese in the near future.

Normal and diseased skinThis subject has been extensively reviewedby Vahlquist (1994). Retinol and several otherretinoids have been detected in the skin,mainly in the epidermis. Some years ago,when clinical signs and symptoms were re-lied upon for the diagnosis of nutritional defi-ciency disease, hyperkeratosis of the skinaround hair follicles was frequently attributedto vitamin A deficiency. This change did notcorrelate with xerophthalmia or serum retinol.At present the general view is that the skindoes not undergo any characteristic clinicalchange in vitamin A deficiency.

In recent years numerous retinoids havebeen synthesized for use in the treatment ofa variety of dermatological disorders (seeChapter 10).

Reproductive systemsStudies in experimental animals have shownthat vitamin A is necessary for the proper func-tioning of both male and female reproductiveorgans. The subject has been reviewed byEskild and Hansson (1994). In the male sper-matogenesis is impaired and the functions ofthe Sertoli and Leydig cells are interfered with.

There is growing evidence that vitamin A,in some form, is required for every stage inthe reproductive process in the female. Thisis in addition to the implication of both defi-ciency and excess of vitamin A during the or-ganogenetic period in the production of mal-formations of the fetus discussed elsewhere(see Chapters 3, 10 and 11).

Other systemsVitamin A deficiency in cattle has a markedeffect on the modelling of bone. Most notablythis has led to compression of the optic nervein the optic foramen, leading to blindness.

Experimentally keratinizing metaplasia hasbeen described in the cochlea in the inner ear.


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Chapter 8

GLOBAL OCCURRENCE

Introduction

The magnitude of the problem of VADDthroughout the world, within a nation, and incertain regions of a nation, is clearly of para-mount importance for the implementation ofmeasures aimed at controlling the problem.Identification of VADD in the first place andmonitoring the progress of control measuresrequire data-collecting systems to be in placeand operating.

Global occurrence

Up to the 1950s there were reports of en-demic xerophthalmia in India, Indonesia andseveral other countries but little more wasknown. The World Health Organization spon-sored a global survey in the early 1960s inwhich three consultants visited about 50countries where VADD was suspected to bea public health problem (Oomen, McLaren,Escapini, 1964). This revealed the wide-spread nature and serious magnitude of theproblem, especially in much of South andEast Asia, and parts of Africa and LatinAmerica. Estimates of the worldwide mag-nitude of the problem were also made(McLaren, 1962;Sommer, 1982).

In recent years the Nutrition Unit of theWorld Health Organization in Geneva, Swit-zerland, with its worldwide contacts, has takenon the role of collecting and disseminating

data. The data file MDIS (Micronutrient Defi-ciency Information System) of the NutritionUnit of the WHO is continuously updated.

This process culminated in the publishingin 1995 of a monograph, Global Prevalenceof Vitamin A Deficiency (WHO, 1995), whichis the most complete database in the field todate. The results of surveys reported fromeach country, where data are available, arepresented in two disaggregated tables: 1) forprevalence of ocular signs and symptoms,and 2) for serum retinol levels. On the basisof these data, and making allowance for par-tial coverage of a country by multiplicationfactors, summary tables and maps by WHOregion were constructed of the prevalence ofvitamin A deficiency (by category: clinical,severe subclinical, and moderate subclinical).Figures 8.1 to 8.7 show the global and re-gional maps updated by October 2000 fromMDIS.

A classification is also presented in tabu-lar form of estimates that have been madefrom the country data of the category occu-pied by each country. As mentioned, WHOkeeps the database under regular review andfrom time to time publishes revised lists ofcountries and their vitamin A status, by WHOregion. Table 8.1 is updated by October 2000from MDIS.

In 1994 the global estimate of the numberof children aged 0–4 years clinically affected


88

GLOBAL OCCURRENCE

Fig

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294

GLOBAL OCCURRENCESIGHT AND LIFE MANUAL

89

Chapter 8

Figure 8.2. Prevalence of vitamin A deficiency in the African Region, based on Figure 8.1 (from infor-mation available to WHO by the year 2000). The designations do not necessarily imply VAD severity isuniformly distributed throughout each country.

Clinical deficiency

Subclinical deficiency

Insufficient data, but possibility of VAD

Insufficient data, but VAD unlikely

Not in region


90

GLOBAL OCCURRENCE

Figure 8.3. Prevalence of vitamin A deficiency in the Region of the Americas, based on Figure 8.1(from information available to WHO by the year 2000). The designations do not necessarily imply VADseverity is uniformly distributed throughout each country.

Clinical deficiency




Not in region


91

Chapter 8

Figure 8.4. Prevalence of vitamin A deficiency in the South-East Asian Region, based on Figure 8.1(from information available to WHO by the year 2000). The designations do not necessarily imply VADseverity is uniformly distributed throughout each country.

Clinical deficiency




Not in region


92

GLOBAL OCCURRENCE

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93

Chapter 8

Figure 8.6. Prevalence of vitamin A deficiency in the Eastern Mediterranean Region, based on Figure8.1 (from information available to WHO by the year 2000). The designations do not necessarily implyVAD severity is uniformly distributed throughout each country.

Clinical deficiency




Not in region


94

GLOBAL OCCURRENCE

Figure 8.7. Prevalence of vitamin A deficiency in the Western Pacific Region, based on Figure 8.1(from information available to WHO by the year 2000). The designations do not necessarily imply VADseverity is uniformly distributed throughout each country.

Clinical deficiency




Not in region


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Chapter 8

Table 8.1. Public health imortance of vitamin A deficiency, from information available toWHO as of October 2000

WHO Clinical Subclinical Insufficient data, Insufficient data,Region deficiency deficiency but possibility of VAD but VAD unlikely

Africa Angola Algeria Cent. African MauritiusBenin Botswana Republic SeychellesBurkina Faso Burundi EquatorialCameroon Cape Verde GuineaChad Congo GabonComoros Côte Guinea-BissauEthiopia d’Ivoire LiberiaGhana Eritrea Republic ofGuinea Gambia CongoKenya Lesotho São Tomé andMalawi Madagascar PríncipeMali NamibiaMauritania SenegalMozambique Sierra LeoneNiger SwazilandNigeriaRwandaSouth AfricaTogoUgandaUnited Republic of TanzaniaZambiaZimbabwe

Americas Argentina Chile Antigua andBelize Cuba BarbudaBolivia Haiti BahamasBrazil Paraguay BarbadosColombia Suriname CanadaCosta Rica Uruguay DominicaDominican Grenada Republic JamaicaEcuador St. Kitts and NevisEl Salvador St. LuciaGuatemala St.Vincent and theGuyana GrenadinesHonduras Trinidad andMexico TobagoNicaragua United States ofPanama AmericaPeruVenezuela

South East Bangladesh Indonesia DemocraticAsia Bhutan Myanmar People’s Rep.

India Thailand of KoreaNepal MaldivesSri Lanka


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GLOBAL OCCURRENCE

(Continued Table 8.1)

WHO Region Clinical Subclinical Insufficient data, Insufficient data,deficiency deficiency but possibility of VAD but VAD unlikely

Europe Israel Albania Azerbaijan Armenia AustriaRomania Belarus Belgium Czech RepublicUzbekistan Bosnia and Herzegovina Denmark Hungary

Bulgaria Croatia Finland FranceEstonia Georgia Germany GreeceKazakastan Kyrgyzstan Iceland IrelandLatvia Lithuania Italy LuxembourgMalta Malta MonacoRepublic of Moldova Netherlands NorwaySlovakia Slovenia Poland PortugalTajikistan Russian FederationThe former Rep. of Yugoslav San Marino SpainRepublic of Macedonia Sweden SwitzerlandTurkey Turkmenistan United KingdomUkraine Yugoslavia


Eastern Iraq Afghanistan Djibouti CyprusMediterranean Somalia Egypt Kuwait

Sudan Islamic Republic of Iran QatarYemen Jordan Lebanon

Libyan Arab JamahiriyaMorocco OmanPakistan Saudi ArabiaSyrian Arab Rep.TunisiaUnited Arab Emirates


Western Cambodia Commonwealth China AustraliaPacific Kiribati of Northern Malaysia Brunei Darussalam

Lao People's Mariana Islands Palau Cook IslandsDem.Rep. Papua New Fiji French PolynesiaMongolia Guinea Guam JapanMarshall Viet Nam Rep. of Korea Islands NauruFederated New Zealand States of Niue Samoa Micronesia Tonga TokelauPhilippines Tuvalu SingaporeSolomon Islands Vanuatu


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Chapter 8

was 2.8 million, and that for severely and mod-erately subclinically affected children was 251million. The report acknowledges a numberof shortcomings and limitations in the data.These were supplied to WHO by the variouscountry authorities and they constitute a veryheterogeneous collection. Many data setsshow weaknesses in survey design, subjectselection, data aggregation, and in informa-tion reporting. With the exception of data fromthe few large research vitamin A interventiontrials reviewed previously (see Chapter 6), thenumber of subjects in the majority of studiesis far too small to meet the minimum samplesize specified by WHO (1996).

Many of the studies used either clinicalsigns or serum retinol, but not both as rec-ommended. This makes categorization diffi-cult. Corneal scar related to vitamin A defi-ciency (XS) is an indicator of deficiency in the

Table 8.2. Preliminary assessment of vitamin A status of a population (after Sommer,1995)

1. Interviews, by structured questionnaire, with central and provincial public health offi-cials, clinicians, nutritionists, community health workers, directors and staff of hospitals,feeding and rehabilitation centres, and schools for the blind.

2. Chart reviews at hospitals, clinics, institutions where children suspected to suffer fromcorneal destruction, or where coded charts do not exist, records from malnutrition, in-fectious diseases, paediatric and ophthalmic services.

3. Search for clinically active cases among children in high-risk situations – hospitals,clinics, impoverished communities.

4. Search for old, healed disease in schools for the blind etc.

5. Collect existing data on child rearing, including breast and other feeding and hygienepractices.

past and is thus unsuitable for inclusion inprevalence data. Xerophthalmia was reportedas “clinical vitamin A deficiency”, making nodifferentiation between blinding (corneal) andnon-blinding (non-corneal) xerophthalmia. Itwould have been useful to have an estimateof the number of cases of blindness beingproduced annually. This could be comparedwith those of other causes of blindness.

MethodologyIt is evident that careful attention should begiven to the methods used for data collectionon the prevalence of VADD. In a country orarea where there has been no previous studyit is advisable to employ a preliminary assess-ment, along the lines of that advised by WHO(WHO Expert Group, 1982). Table 8.2 indi-cates the kind of background data that shouldbe sought in the first instance.


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GLOBAL OCCURRENCE

This can be done in a simple way that iseconomical of personnel and resources. It willbe observed that most of these data relate tothe detection of a problem of xerophthalmia.If the health concern is at the subclinical levelof VAD then an assessment may be madeusing the socioeconomic and ecological indi-cators recommended by WHO (1996). Onlyif the results are highly suggestive of the pres-ence of a significant problem should a fullpoint prevalence survey be embarked upon.This is much more expensive and time-con-suming and should be carried out meticu-lously if the results are to be relied upon(Sommer, 1995).

Figure 8.8. Trends in xerophthalmia in children up to six years (ACC/SCN Con-sultative Group, 1994).

Country situationsThere is still a surprisingly large number ofcountries from which no data are availableand where the occurrence of a problem mightbe suspected (see Table 8.1). The largestblock of such countries is that of the formerSoviet Union with millions of children at risk.

The situation is, of course, fluid and theremay be improvement or deterioration overquite a short period of time. For example,there is good evidence that the situation hasimproved considerably in three of the majorcountries where VADD was highly endemiconly two decades or so ago (see Figure 8.8).


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Chapter 8

In the Philippines in 1993 a National Nutri-tion Survey carried out by the Food and Nu-trition Research Institute showed that clinicalVAD prevalence among six-month- to six-year-old children was 0.4% for XN and 0.2%for X1B, and for the total population preva-lence of XN was 0.8% and of X1B 0.3%, indi-cating that VAD is no longer a clinical publichealth problem (as shown in Figure 8.7 andTable 8.1). However, serum retinol <0.35µmol/L among six-month- to six-year-old chil-dren occurs in more than 5% in 11 out of 15regions. Low serum retinol (<0.70 µmol/L)occurs in 24.9%. These results suggest thatat present the Philippines should be catego-rized to have a severe subclinical VAD publichealth problem (F. Solon, personal commu-nication).

Xerophthalmia was extremely common inVietnam until after the cessation of hostilities.

In recent years, highly efficient capsule dis-tribution nationwide has resulted in a pro-nounced decrease (Khoi, Khan, Thang et al,1996). Sometimes improvement is more likelyto be attributable to general economic andsocial development, rather than just to spe-cific vitamin A interventions.

On the other hand, VADD has emerged inseveral countries in the Pacific region, as aresult of rapid changes in lifestyle and theabandonment of traditional dietary and otherpractices that were protective (Lloyd-Puryear,Humphrey, West et al, 1989; Schaumberg,O’Connor, Semba, 1996).

In other countries a public health problemhas long been suspected but data were notavailable. This seems to be the situation inLaos (Malyavin, Bouphany, Arouny et al,1996) and is true for Afghanistan.


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Chapter 9

EPIDEMIOLOGY

IntroductionEpidemiology may be defined as the study ofthe distribution and determinants of diseasein a population. In simple terms various partsof the Manual may be considered to havedealt in turn with the answers to different ques-tions about VADD. For example the first fourchapters described how VADD occurs. Chap-ters 5–7 stated what VADD causes. Chapter8 dealt with where VADD occurs and howmuch there is. The present chapter sets outto give some answers to the question “whydoes VADD occur?”. A clear understandingof these matters is vital before appropriatemeasures can be taken for the control ofVADD. It is logical that this chapter on epide-miology should precede Chapter 11 on “whatcan be done?”.

Those factors that are closely associatedwith the occurrence of a disease are knownas risk factors. This association may be dem-onstrated by the application of statistical meth-ods. However, there is no statistical way ofproving that the association is causal; i.e. thatthe factor causes the disease. A logical rela-tionship between the factor and the diseaselends support to the association being causal,but does not provide proof.

Consequently, epidemiology can provideuseful indications as to how a disease arises.Vulnerable groups can be identified towardswhom interventions may be targeted. Defec-tive or, on the other hand, protective aspects

of diet and other aspects of lifestyle may berevealed and as a result this knowledge maybe used in planning interventions.

It is important to recognize that epidemio-logical factors may vary considerably fromplace to place. Interventions need to be ap-propriate for local conditions. For example,in some circumstances it may be found thatthe weaning diet lacks rich sources of provi-tamin A in the form of dark green leaves oryellow fruits. Ways should be sought to en-sure that these are incorporated into theyoung child’s diet if at all possible. On theother hand, it may be found that dietary in-take of carotenoids is adequate but VADD isnevertheless a problem. Further investigationmay reveal that there is heavy round-worminfestation in the community and it is likelythat much of the ingested carotene is not be-ing absorbed. Deworming and measures toimprove sanitation should have priority in thiscase.

There is no special order in which the riskfactors are considered here, but in generalthose of greater importance are taken first.

AgeEvidence from every source agrees that pre-school age children form the most vulnerablegroup (Sommer, 1982). This applies to cor-neal xerophthalmia in hospitals (see Figure9.1) and non-corneal xerophthalmia in fieldstudies (see Figure 9.2). Of the data taken


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EPIDEMIOLOGY

Figure 9.1. Age distribution of consecutive cases with corneal xerophthalmia (X2 or X3) presenting tothe Cicendo Eye Hospital (n=162), Bandung, Indonesia, and to the Lahan Eye Hospital (n=295),Nepal (Sommer, West, 1996, p 337).

together it will be evident that the more seri-ous lesions peak at an earlier age than theless serious.

A combination of factors probably lies be-hind this phenomenon. The requirements forgrowth of the younger child tend to be greater,while the body stores tend to be lower. Thediet of the vulnerable child tends to be morerestrictive and limited during infancy or justafter weaning than later on. Infections havean additional adverse nutritional impact.

Keratomalacia in the infant usually pro-ceeds rapidly without any tendency for xero-sis of the conjunctiva to develop. From someparts of India there have been recent reportsof increase in the occurrence of infantkeratomalacia. This may be related to the in-creasing practice of women of low socioeco-nomic status to go out to work and to leave

their infants at home without adequate atten-tion (Rahmathullah, Raj, Darling et al, 1994).

School age is another period of increasedsusceptibility, usually involving the milderdegrees of xerophthalmia (night blindness orBitot’s spots) (Khan, Haque, Khan, 1984).This may be due to increased requirementsfor growth, especially during the adolescentgrowth spurt (Ahmed, Hasan, Kabir, 1997).

Physiological statusIt has long been recognized that the pregnantand lactating woman is especially vulnerable.Recently some very high rates have beenreported especially from the Indian subconti-nent (Katz, Khatry, West et al, 1995). In thisstudy from Nepal 16.2% of women reportedXN at some time during the pregnancy thatproduced the child they were breast-feeding

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Figure 9.2. Age distribution of mild xerophthalmia in selected countries in Asia and Africa: Nepal,Zambia, India and Indonesia (showing data from both countrywide surveys in 1978–79 and 1992)(Sommer, West, 1996, p 338).

at the time of the interview. 8.1% reported XNat the time of the interview. The chances ofXN in the current pregnancy were six timesgreater for those who reported XN in their pre-vious pregnancy than for those who did not.

Only mild xerophthalmia is usually seen andthe mother’s health may not be permanentlyaffected. However, low vitamin A content ofbreast milk will contribute to the increasedsusceptibility of the infant. The proposal thatbreast milk retinol be used as a biological in-dicator of vitamin A status in the communitywas discussed in Chapter 4.

More recent studies by the same group inNepal have shown that XN in pregnancy may

be a marker of other nutritional and healthrisks (Christian, West, Khatry et al, 1998). At-titudes of women towards XN have beendocumented (Christian, Bentley, Pradhan etal, 1998) as has the extent to which it impairstheir work activities (Christian, Thorne-Lyman,West et al, 1998).

DietRegular ingestion of the customary dietariesaround the world, both now and in the past,has provided for vitamin A requirements tobe met. It has only been when consumptionwas limited, perhaps at certain seasons ofshortage or when certain food items wereomitted altogether, that problems have arisen.


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Young children have to rely on others to feedthem, and pregnant and lactating women aresometimes especially targeted for food ta-boos.

Staple foods, mostly cereals but includingsome starchy roots, provide the bulk of a diet.They generally contain small concentrationsof carotenoids but because they are eaten inbulk the amount supplied may be consider-able. Rice is the main exception to this rule.It contains no carotenoids in the form in whichit is consumed (see Chapter 11). Furthermore,it is often considered to be a complete dietfor the young child by the mother. Infants findit easy to eat and satisfying. “Rice-depend-ent” communities, where rice and little elseforms the daily diet, have proved to be espe-cially prone to suffer from VADD. It is ironicalthat this situation occurs mainly in the moisttropics, where carotene is readily availableon every hand. This is truly an instance ofnutritional “poverty in the midst of plenty”(McLaren, 1962).

Enquiries about dietary intake should startwith identification of the staple food. In thisway the traditional “home” of xerophthalmiawas found to be the rice-dependent areas ofsouth and east Asia. In India the rice-eatingsouth has been much more vulnerable thanthe wheat-eating north. On some of the smallislands of Indonesia maize is the staple food,and xerophthalmia was virtually confined tocommunities that consumed white maize(carotene-free) and not seen among thosethat ate the yellow variety (Oomen, 1961).

Recent studies continue to provide evi-dence for the close relationship between VADand the details of dietary intake and culturalpractices, especially in young children(Hudelson, Dzikunu, Mensah et al, 1999).Adverse factors are large family size(Kjolhede, Stallings, Dibley et al, 1995), shar-ing of the food plate with an adult male ratherthan a female family member (Shankar,

West, Gittelsohn et al, 1996) and lack of childcare (Gittelsohn, Shankar, West et al, 1998).Feeding practices in infancy can influencesubsequent risk for VAD (Gittelsohn, Shan-kar, West et al, 1997). Preformed vitamin Aintake may be more important than caroten-oid-containing foods for the protection of chil-dren and others (Shankar, West, Gittelsohnet al, 1996).

Breast-feedingThere is abundant evidence that breast-feed-ing is highly protective against xerophthalmia(Sommer, West, 1996, pp 343-345). This maybe partly due to the regular supply of pre-formed vitamin A in the milk. Another impor-tant factor is the lower rate of infections ascompared with artificially fed children. A studyin south India (Ramakrishnan, Martorell,Latham et al, 1999) showed that whilenonbreast-fed children met only 60% of theIndian RDA, those breast-fed met 90% dur-ing the second year of life. WHO and UNICEFrecommend that all infants be exclusivelybreast-fed for at least 4 and if possible 6months and that they continue to be breast-fed up to two years or beyond with the addi-tion of adequate complementary foods fromabout 6 months of age.

The composition of the weaning diet is ob-viously of great importance. Infrequent con-sumption of dark green leaves or yellow fruitswas associated with four- to sixfold increasein the risk (odds ratio) of xerophthalmia in onestudy (see Figure 9.3).

Cultural factorsThe customs practised by a community areusually deeply embedded within the fabric ofthe society. They are not as open to under-standing by outsiders as are less complicatedcharacteristics like others considered here.Groups under study often speak a languagenot readily understood by the investigators,


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Figure 9.3. Relative risk (case-control odds ratio) (±95% CI) of mild xerophthalmia (vitamin A defi-ciency) by type of food reportedly consumed by children daily or every other day during their firsttwelve months of weaning (Mele, West, Kusdiono et al, 1991). Not eating dark green leaves e.g.,increases the risk about sixfold.

even if of the same country. For outsiders,and this is what scientists investigating a com-munity inevitably are, understanding theworldview of others is always limited.

More than forty years ago (McLaren, 1956)the apparent protection of the children of atribal group in an area of south India wherekeratomalacia was highly endemic was attrib-utable to the custom of child-spacing prac-tised by this group, but not practised by an-other group among whom corneal xerophthal-mia was common. In this rice-dependent stateof Orissa, India, the “deposed child” was thetarget of keratomalacia. This phenomenonhad first been described in Ghana (Williams,1933) where the victim of kwashiorkor wasthe child who had been abruptly weaned whenthe mother realised she was pregnant again.It is of considerable interest that in both in-stances the investigators made their contri-

butions as by-products of their primary workand from long and intimate contact with thepeople concerned.

Infectious diseasesAs was noted earlier, when the topic of theimpact on infections of vitamin A deficiencywas considered (see Chapter 6), the relation-ship is complex. Infections also predisposeto the development of vitamin A deficiency,as will be considered here.

Systemic infections

Sommer and West (1996, pp 191-220) havereviewed the extensive evidence that a vari-ety of infections are associated with a decline,often dramatic, in serum retinol levels. It isonly in recent years that this phenomenon hasreceived the attention it deserves. The fall in


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serum retinol is usually greatest in acute andsevere infections and there is a return to pre-infection levels during recovery. However,even a normally trivial illness like chicken poxmay have a dramatic and prolonged effect inreducing serum retinol, even in children whopreviously appeared healthy.

The fall in serum retinol appears to be partof what is known as the acute-phase proteinreaction (Smith, Goodman, 1971). Serumlevels of C-reactive protein and other pro-teins rise in response to significant infectionsand other insults. It is thought that these re-sponses may be set in motion by proin-flammatory cytokines produced early on bythe infection. On the other hand there is evi-dence (Rosales, Ritter, Zolfaghari et al,1996) that this results in suppression of thesynthesis of transport proteins like albuminand RBP by hepatocytes. These proteinsmay also be diverted from the plasma intothe extra-cellular space, resulting in de-creased serum levels. This phenomenon hasbeen studied in pregnant women in relationto their experiencing illness symptoms andnight blindness (Christian, West, Khatry etal, 1998a).

An important implication of these observa-tions is that care must be exercised in theinterpretation of serum retinol levels, in rela-tion to the assessment of vitamin A status,including their use in relative dose-responsetests, in subjects who may be harbouring aninfection at the time.

There is every likelihood that vulnerablechildren frequently become trapped in a cy-cle of infectious disease and increasing vita-min A deficiency which potentiate the effectof each other. This can lead to serious con-sequences of morbidity and death.

Diarrhoeal diseases

There is strong evidence from both clinicaland field studies that diarrhoeal disease isclosely associated with xerophthalmia andwith impaired vitamin A status.

Considerable interest was aroused by thereport from Peru (Alvarez, Salazar-Lindo,Kohatsu et al, 1995) that diarrhoeal disease,especially that due to rotavirus infection andwith accompanying high fever, may lead toas much as a tenfold increase in the urinaryexcretion of vitamin A (see also Table 10.1).Alvarez and colleagues reported a similarurinary loss of vitamin A in adults with sepsisand pneumonia in the United States and haveextended their studies to Bangladesh (Mitra,Alvarez, Stephensen, 1998). In shigellosisurinary retinol loss was proportional to theseverity of the disease, and impaired tubularreabsorption of low molecular weight proteinslike RBP appeared to be the cause.

Intestinal parasites

Giardia lamblia, Ascaris lumbricoides, (round-worm) and Ankylostoma duodenale (hook-worm) have all been shown to reduce vita-min A absorption, and in some instances tobe associated with clinical VAD (Curtale,Pokhrel, Tilden et al, 1995). The impact maybe greater on absorption of carotenoids thanon absorption of preformed vitamin A. Mostof the population becomes infested wheresanitation is lacking. Deworming programmesfail to have a long-term impact in the absenceof improvements in sanitation and the break-ing of the cycle of transmission.

Respiratory diseases

As was the case for diarrhoeal diseases, alsofor respiratory infections there is good evi-dence from field and hospital studies that theyworsen vitamin A status at all levels. Several


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Table 9.1. Corneal ulceration within one month of measles infection by cause and ageas a percentage of all ulcers in Tanzanian children (Foster, Sommer, 1987)

Age Xerophthalmia Herpes simplex Traditional(years) eye medicine

N n % N n % N n %

<2 16 10 62 24 3 12 8 1 12

2–4 12 11 92 10 3 30 5 5 100

5–10 6 3 50 13 4 31 5 2 40

Total 34 24 71 47 10 21 18 8 44

N=total numer of children seen with corneal ulceration due to a specific cause; n=number of childrenseen with corneal ulceration due to a specific cause which developed within one month of measlesinfection

possible mechanisms may be at work includ-ing loss in urine and impaired absorption ofboth vitamin A and carotenoids (Sommer,West, 1996, pp 191-220).

Measles and associated conditions

The effect of vitamin A deficiency on thecourse of measles infection was discussedearlier (see Chapter 6). Decades ago mea-sles was recognized to carry a high mortalityrisk in children in Africa with severe PEM, andinvolvement of the eye was occasionallynoted. It took many years to provide the evi-dence that was necessary to bring about gen-eral acceptance of the fact that vitamin A de-ficiency is frequently responsible for the blind-ness that sometimes followed an attack ofmeasles. There is evidence from other partsof the world, as well as from several regionsof Africa, that about one quarter to one half ofall cases of corneal blindness in young chil-dren are associated with measles (Sommer,West, 1996, pp 191-220).

It is now recognized that often there is notonly the combination of VAD and measles butthat other factors may also play a part. Some-times the initial eye involvement is treated bythe application of traditional eye medicines thatusually serve to increase the damage. Ulcera-tion in the periphery of the cornea, especiallyin otherwise quiet eyes, is then characteristic(Lewallen, Courtright, 1995). Severe involve-ment of the cornea may be due to superaddedinfection with the herpes simplex virus (seeTable 9.1). In this series of cases of cornealulceration treated in hospital there is a higherproportion of cases following measles infec-tion in the group with xerophthalmia as a spe-cific cause than in those in which herpes sim-plex or traditional eye medicine was the cause.This is perhaps not surprising as severe mea-sles tends to precipitate nutritional deficiency.

This combination has been reported fromseveral parts of Africa but is not known to havethe same importance elsewhere. Malaria hasalso been reported to be a precipitating factorin some places (Yorston, Foster, 1992; Genton,


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Al-Yaman, Semba et al, 1994). This merits in-vestigation elsewhere in view of the wide-spread occurrence of drug-resistant malaria.

HIV/AIDSOnly in recent years has the association be-tween HIV infection and vitamin A status be-gun to be investigated (see Chapter 5). Thereis no evidence yet as to whether infectionimpairs vitamin A status. It is likely that a se-rious disease like AIDS would have such aneffect, and the reverse is certainly so.

Protein-energy malnutrition(PEM)

Impaired growth usually accompaniesxerophthalmia and tends to increase paripassu with the degree of vitamin A deficiency(see Chapter 7). Severe degrees of PEM,evidenced clinically as marasmus, marasmic-kwashiorkor, or kwashiorkor, are not neces-sarily associated with eye signs of xeroph-thalmia, although serum retinol is usually de-pressed. Corneal xerophthalmia on the otherhand is usually accompanied by severe PEMin some form (McLaren, Shirajian, Tchalianet al, 1965).

Much of the association can be explainedby dietary habits and disease patterns thatat the same time adversely affect both pro-tein energy and vitamin A status. In addi-tion, there is both experimental and clinicalevidence that low protein status can impairRBP synthesis and its release from the liver.Therefore the RBP response to a large doseof vitamin A is reduced (Sommer, West,1996, p 207). Low protein status can im-pair response to vitamin A therapy and de-lay recovery of corneal xerophthalmia(Sommer, West, 1996, p 207). However, inchronic protein deficiency growth and meta-bolic demands are inhibited and when pro-

tein is given therapeutically vitamin A de-mands may be increased and xerophthal-mia precipitated.

SeasonFluctuation in the amount of vitamin A andcarotene available in the diet throughout theyear is well documented (Moore, 1957).Where sources are limited the change is re-flected in variations in plasma levels of vita-min A and the seasonal occurrence of signsof vitamin A deficiency. Cattle fed on winterfodder produce milk with a lower vitamin Acontent than when they receive summer pas-ture. In developing countries yellow fruits likemangoes and papaya are usually consumedduring their quite short seasons and may notbe stored. Leafy vegetables have longer, butstill limited, seasons. Communities often ex-perience an annual dry, “hungry” seasonwhen young children and their mothers tendto suffer most (Oomen, 1969). Failure of therains or, conversely, excess flooding for sev-eral years in succession can lead to seriousfood shortage or even famine. Under suchconditions outbreaks of night blindness andother deficiencies tend to affect a high pro-portion of the total population.

Among communities that subsist in semi-desertic terrain, as in the deserts of Rajasthan(Desai, Desai, Desai, 1992), a single seasonwith a lack of monsoon rainfall can spell nu-tritional disaster (Fig 9.4).

Frequently superimposed upon the sea-sonal pattern described above there is theadded effect of seasonal outbreaks of infec-tious diseases (Oomen, McLaren, Escapini,1964; McLaren, Shirajian, Tchalian et al,1965). The most important of these is thegroup of diarrhoeal diseases, gastro-enteri-tis, often known locally as “summer diarrhoea”because of its peak season. VAD is usuallyaccompanied by PEM and emerges towards


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Figure 9.4. The yearly prevalence of xerophthalmia in a population of children aged less than 10years shows a peak of 34.3% in 1987, the year of severe drought in western Rajasthan (Desai,Desai, Desai, 1992).

the end of the diarrhoea season, as the ef-fects of prolonged and repeated attacks ofdiarrhoea take their toll.

Respiratory infections tend to peak in thewinter, which in some developing countrieswith a continental climate or at high altitudemay be bitterly cold.

The most precise documentation of sea-sonal patterns and VADD was made by Sinha,

who resided for two years in the West Ben-gal village area of Ichag (see Figure 9.5).

Socio-economic statusEconomic deprivation was found in thecountrywide survey in Indonesia (Sommer,1982) to correlate closely with vitamin A sta-tus. Other indices of health have shown thesame thing, as did for example growth ofyoung children in Lebanon (Kanawati, McLa-ren, 1973).


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Figure 9.5. Seasonal prevalence of vitamin A deficiency signs, Ichag, 1971–73 (Sinha, Bang, 1976).

LocationSommer and West (1996, pp 335-354) sum-marize a large body of evidence that showsthat VADD tends to cluster at a variety of lev-els. This phenomenon applies to provinces,districts, subdistricts, villages and households(IVACG, 1996a). Figure 9.6 shows this clus-tering in regions in Bangladesh.

In some countries childhood blindness haslong been known to be a special feature ofcertain remote regions. The Luapula Valleyin Zambia (Sukwa, Mwandu, Kapui et al,1988) and the Lower Shire Valley in Malawi(West, Chirambo, Katz et al, 1986) are twoespecially well studied examples. Vitamin Adeficiency has proved to be the major causeof childhood blindness in both places. Theunderlying reasons have proved to be com-plex.

As for any disease, the occurrence of clus-ters may be seen as the probable presenceat one time and place of a combination insome degree of intensity of several of the risk

Figure 9.6. Regional clustering of VAD by sever-ity and district in Bangladesh (Cohen, Rahman,Mitra et al, 1987).

X1B >1%XN >3% and X1B <1%XN <3% and X1B <1%Not surveyed


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Chapter 9

Figure 9.7. The prevalence of Bitot’s spots increased significantly (p >0.01) at 1, 2, and 3 years ofage. Bitot’s spots were more common among boys (12.5/1000) than among girls (7.2/1000)(p <0.001) (Sommer, 1982).

factors considered here. There might also beother variables that are as yet unrecognized.

Katz, Zeger, West et al (1993) have stud-ied clustering of xerophthalmia within house-holds and villages in Malawi, Zambia, Indone-sia and Nepal. The magnitude of clusteringvaried between countries and in all placesstudied it was much greater within householdsthan within villages. Infectious diseases ap-peared not to explain much of the clustering.Other household factors related to diet andnutrition are suspected to be more important.

Identification of clustering can considerablyinfluence the implementation of an interven-tion. In Nepal it was estimated that measuresto prevent xerophthalmia were 7–34 timesmore efficient in high-risk, highly populatedareas than in remoter communities (West,Pokhrel, Khatry et al, 1992).

WHO (1996) has proposed a number ofecological indicators of VAD assessment tobe used in conjunction with biological indica-tors (see Chapter 4). Most of these have beenreferred to elsewhere in this chapter.

SexMost of the evidence from animals and hu-mans suggests that males are more suscep-tible to VAD than females. In healthy humanadults plasma retinol and RBP are both about20% higher in males, but the significance ofthis is unclear (Pilch, 1987; Smith, Goodman,1971). Night blindness and Bitot’s spot arealmost uniformly reported to be from 1.2 to10 times more common in males (Paton,McLaren, 1960; ten Doesschate, 1968; So-lon, Popkin, Fernandez et al, 1978). Theseselected samples were supported by thecountrywide survey in Indonesia (Sommer,


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Figure 9.8. Seasonal prevalence of vitamin A deficiency (night blindness and/or Bitot’s spot) accordingto sex, Ichag, 1971–73 (Sinha, Bang, 1973).

1982) with about twice as many Bitot’s spotsin males as in females (see Figure 9.7).

Interestingly, no evident sex difference wasfound in the detailed longitudinal study ofSinha and Bang (1973) (see Figure 9.8).Prevalence of VAD was extremely high in thisarea. Not only did it reach an astonishing peak

of 15 to 16% in both sexes at the beginningof the rainy season; it never fell to a rate be-low that of the WHO criteria (1% and 0.5%).

Male preponderance was again found in thelargest hospital series ever reported (Oomen,1961) from the eye hospital of Dr Yap Kie Tiongin Jogjakarta, Indonesia (see Figure 9.9).


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Figure 9.9. Age distribution of 6300 cases of xerophthalmia in the Yap Eye Hospital at Jogjakarta,Indonesia, from 1935 to 1954. The male preponderance throughout increases with age (Oomen, 1961).


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Among the 6300 cases the male:femaleratio varied with age. It was 1.4:1.0 in the pre-school age period, and 6.0:1.0 at around 10years of age.

In some cultures in hospital studies malechildren will tend to appear preferentially be-cause medical attention is more likely to besought for them.

The Vitamin A DeficiencyDisorders (VADD) cycle

This flow diagram (see Figure 9.10) has beendevised to give some impression of the kindof combinations of risk factors that conspiretogether at different stages of the life cycle topredispose to the development and persist-ence of a VADD problem in a community.

Figure 9.10. The Vitamin A Deficiency Disorders (VADD) cycle.


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Chapter 10

RETINOIDS IN GENERALMEDICINE

IntroductionIn addition to the various aspects of the glo-bal problem of VADD with which this Manualis primarily concerned, there are other closelyrelated and rapidly expanding areas of inter-est that concern retinol and other retinoids ina human health context. The intent in thischapter is to touch on these and to indicatewhere more detailed information can be ob-tained if desired.

In addition to arising from some deficiencyin the dietary intake of vitamin A, VADD mayalso occur as a result of some defect in thethe body’s physiology or metabolism. Thismay be called secondary or endogenous, asopposed to exogenous VAD, and attention willbe given here to a variety of forms that it cantake.

There is an increasing number of diseasesin which dosing with vitamin A appears to havea beneficial effect, even in the absence of anydeficiency. This area is clearly a part of thevitamin A story and is rightly receiving con-siderable interest at present.

Vitamin A is one of the vitamins that canlead to disease as the result of not only defi-cient, but also excessive, intake. This is usu-ally known as hypervitaminosis A. This mayarise as the result of prophylactic or thera-peutic use of vitamin A as will be discussed

later in Chapter 11. Some aspects of the ex-cessive intake of retinol or other retinoids aremore appropriately dealt with here.

As mentioned (see p 2 ) when the chemis-try of retinoids was introduced, large numbersof them have been synthesized for use in vari-ous diseases, especially those in which epi-thelial cell differentiation has been disturbed.Some attention will be paid to the topic here.

Finally, many of the carotenoids, irrespec-tive of whether they are provitamins ornonprovitamins, have been shown in recentyears to have the potential to play a protec-tive part, illunderstood at present, in a numberof common diseases. There is growing evi-dence that habitual consumption of diets thatare rich sources of these carotenoids are as-sociated with low rates of some of these dis-eases.

Secondary VADTable 10.1 summarizes the various differentkinds of secondary VAD that have been re-ported to date, together with the mechanisms.In most instances the degree of vitamin Adeficiency is not severe. As little attention isgiven to VAD or any other nutritional defi-ciency in general medicine it is usually notuntil some clinical manifestation, like nightblindness or conjunctival xerosis, occurs thatdeficiency is suspected. Consequently it is


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really not known how common deficiency isin these conditions, especially at the subclini-cal level. The various causes of malabsorp-tion are by no means uncommon and mostcases of secondary VAD have this basis. Onthe other hand only single cases have so farbeen reported of the enzyme defect, the trans-port abnormality and the genetic problem intwins. However, there are indications thatgenetic predisposition to VAD may be of moreimportance than has hitherto been generallyrecognized (Ward, MacGowan, Hornby et al,2000). Larger doses than normal of vitamin Aare required to overcome the metabolic prob-lems present, and where there is impaired fatabsorption a water-miscible preparationshould be given by mouth and perhaps ini-tially intramuscularly. It is often not appreciat-ed that the usual form of oily vitamin A givenintramuscularly stays in the muscle and is notreleased to any extent into the circulation(McLaren, 1969).

Non-nutritional diseasesresponsive to vitamin A

Bronchopulmonary dysplasia (BPD) is theleading cause of chronic lung disease in in-fancy and affects particularly very low birthweight infants. In the United States amongthe 3.9 million or so births annually approxi-mately 55,000 newborns weigh <1500 g atbirth. These are classified as very low birthweight (VLBW). About 49,000 survive hospi-talization and about 24% of these suffer fromBPD. The histological changes in the lungsthat accompany this condition are similar tothose described in children dying with xeroph-thalmia. Most of these infants have serumretinol and RBP in the deficient range. Theyare also born with low liver reserves. Severaltrials have shown benefit from dosing withvitamin A. The usual regime is 5000 IU ofwater-miscible vitamin A intramuscularly threetimes a week for four weeks (Shenai, 1999).The precise requirement of vitamin A, the

Table 10.1. Secondary or endogenouscauses of vitamin A deficiency

Diseases Mechanisms

Coeliac disease, Impaired absorptionsprue, obstructive of lipids, includingjaundice, ascariasis, vitamin Agiardiasis, partial ortotal gastrectomy

Chronic pancreatitis In some casessecondary to zincdeficiency

Chronic liver Storage impaireddisease, especially by damage tocirrhosis liver cells;

zinc deficiencyenhances theeffect

(1) Severe infection Loss of RBP in urine

(2) Cystic fibrosis Excessive faecalloss, unrelatedto degree of fat instools

(3) Enzyme defect Failure to cleaveβ-carotene insmall intestine

(4) Heterozygotic One case reported ofreduction of keratomalacia due toplasma RBP reduced transport

(5) Mutations in the Biochemical but notgene for RBP clinical deficiency

(1) Alvarez, De Andres, Yubero et al (1995)(2) Ahmed, Ellis, Murphy et al (1990)(3) McLaren, Zekian (1971)(4) Matsuo, Matsuo, Shirago et al (1988)(5) Biesalski, Frank, Beck et al (1999)


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Chapter 10 RETINOIDS IN GENERAL MEDICINE

optimal mode and duration of its administra-tion need further investigation.

Experimental model ofemphysema

Emphysema is another common lung dis-ease, affecting about 2 million Americans andcausing the deaths of 17,000 each year. Mostcases are associated with cigarette smokingbut about 5% are caused by a deficiency ofthe enzyme alpha-1-antitrypsin. Emphysemahas been induced in rats by intratracheal in-stillation of a saline solution of elastase whichdestroys elastin fibres leading to collapse ofalveolar walls in the lu“ngs and resulting inemphysema. It has been shown (Massaro,Massaro, 1997) that retinoic acid can reversethe action of elastase and permits the growthof new alveoli. This work holds out hope forthe development in future of a treatment inhuman disease. Chytil, (1992) has reviewedthe role of retinoids in lung physiology.

Retinitis pigmentosa andsome other retinopathies

As was pointed out in Chapter 4 in additionto VAD several other diseases affecting theretina may also have night blindness as partof their symptomatology. Almost all of theseare rare genetic disorders. Retinitispigmentosa (RP) affects about 1 in 4000worldwide and eventually leads to total blind-ness. There are many different genetic formsof the disease. Over many years claims havebeen made for improved vision with vitaminA and other treatments, but the only large,fully controlled trial with vitamin A over a pro-longed period was carried out in the UnitedStates (Berson, Rosner, Sandberg et al, 1993).The claim was made that patients receivingvitamin A tended to experience a slowing inthe rate of deterioration of their electroretino-gram, compared with those who did not.

There was no improvement in vision. Therewas considerable controversy about thesefindings at the time. The publicity the reportreceived has unfortunately meant that manypatients have started self-medication with vi-tamin A in the absence of any proven treat-ment. The equivocal nature of the results mayhave been at least in part due to the mixednature of RP cases included in the trial. Re-cent evidence suggests that some forms ofRP may be more likely to respond than oth-ers (Fariss, Zong-Yi, Millam, 2000). Other rarediseases in which vitamin A has brought aboutsome improvement in rod function areBassen-Kornzweig Syndrome and SorsbyFundus Dystrophy (Berson, 1999).This wholecomplex subject was discussed at greaterlength recently (McLaren, 2000).

Hypervitaminosis AVitamin A toxicity may be either acute orchronic. Acute toxicity usually follows a largesingle dose of vitamin A and is recognised bysymptoms that suggest an acute rise in in-tracranial pressure – nausea, vomiting andheadache. Providing no further vitamin A isgiven symptoms rapidly subside and there areno permanent ill effects (see Chapter 11). Thesubjects have usually been young children ina supplementation programme or arctic ex-plorers short of food who have consumed theliver of polar bear, seal or their own sled dogs.

Chronic vitamin A toxicity is uncommon butmay be very difficult to diagnose. This is partlybecause the physician may neglect to take acareful dietary history and routine clinicallaboratories are not usually capable of meas-uring serum retinol. Perhaps even more im-portant is the fact that the symptomatology ofhypervitaminosis A may be very varied, af-fecting a number of different systems andsometimes mimicking other diseases.Common symptoms are headache, vomit-ing, diplopia, alopecia, dryness of mucusmembranes, desquamation, bone and joint


118


pain, liver damage including cirrhosis, haem-orrhages into the skin and coma. If not cor-rectly diagnosed and further excessive vita-min A intake is prevented, death can result.

Congenital malformationsIn experimental animals both vitamin A defi-ciency and toxicity have been known for a longtime to induce congenital malformations. Inseveral animal models similar malformationshave been regularly produced by syntheticretinoids.

In humans the evidence for the involvementof deficiency of vitamin A is slender, amount-ing mainly to isolated case reports. A defini-tive report of a study of the effect of maternalvitamin A or β-carotene supplementation onthe incidence of birth defects in Nepalese in-fants (Khatry, LeClerq, Adhikari et al, 1997)is awaited with interest. In striking contrast,there are numerous reports of high incidences(>20%) of spontaneous abortions and birthdefects in the fetuses of women ingestingtherapeutic doses of 13-cis RA and otherretinoids during the first trimester of preg-nancy (Ross, 1999).

The most controversial area has been thepossible teratogenic effect of excess vitaminA intake during early pregnancy. The presentconsensus is that in communities where VADis known to be present vitamin A supplemen-tation throughout pregnancy should not ex-ceed 10,000 IU per day (see also Chapter11). Where the diet supplies the RDA andmore, even this level may be excessive. Evenso, a recent Europe-wide study found no as-sociation between high vitamin A intake inearly pregnancy and major malformations(Mastroiacovo, Mazzone, Addis et al, 1999).120 infants exposed to more than 50,000 IUdaily showed no malformations. Another verylarge study from Europe (Czeizel, Rocken-bauer, 1998) reported on the population-based data set of the Hungarian Case-Con-

trol Surveillance of Congenital Abnormalitiesfor 1980–94. This included 35,727 normalinfants and 20,830 infants with congenitalabnormalities of all kinds. The mothers of3399 (9.5%) of the normal infants receivedvitamin A supplements, as did 1642 (7.9%)of those who had infants with malformations.The difference was highly significant(p<0.001). It was suggested that this analy-sis was in favour of low or moderate doses ofvitamin A being protective, and not tera-togenic. An additional analysis, not pursuedby the authors, is to group the infants accord-ing to whether or not their mothers receivedvitamin A and to compare the numbers ofthose with malformations in each group. Of5041 receiving vitamin A 1642 (32.5%) hadmalformations ; of 51,516 not receiving vita-min A 19,188 (37.2%) had malformations. Thisdifference is also highly significant at thep<0.001 level and also suggests that vitaminA might be protective. All of the evidence avail-able to date is reassuring with regard to thesafety of the use of vitamin A supplementsaccording to generally accepted practice.

Pharmacological use ofsynthetic retinoids

Dermatology

Natural and synthetic retinoids influence epi-thelial cell proliferation and differentiation andare increasingly being used in dermatologi-cal practice to treat hyperkeratotic disorders.Etretinate and acitretin are very effective inpsoriasis. 13-cis retinoic acid and retinoyl-β-glucuronide suppress sebum productionand are used in acne and acne-related disor-ders (Figure 10.1). Tretinoin has a beneficialeffect in some cases of actinic keratosis,caused by chronic exposure to sunlight. Atpresent only three retinoids are approved fororal administration in many countries;isotretinoin, etretinate, and acitretin. Theirteratogenic effects were discussed above.


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Cancer chemoprevention and treatment

Many studies in experimental animals haveshown the ability of both natural and syntheticretinoids to reduce carcinogenesis in organssuch as breast, skin, liver, colon, prostate,lung and other sites. Natural retinoids are tootoxic for prolonged use in man, but some syn-thetic retinoids are well tolerated and havethe potential for prophylactic use. In recentyears attention in this field has turned moreto the potential of some carotenoids to act asagents in chemoprevention of cancer andsome other conditions (see below).

At present retinoid treatment of cancer isconfined to one retinoid and one form of can-cer. Acute promyelocytic leukaemia (APL) isa form of leukaemia which is a group of ma-lignant neoplasms affecting the cells of theblood-forming tissues. In APL chromosome15 is abnormal with a translocation that af-fects the gene for RAR-alpha (Norum, 1994).All-trans RA is highly effective in bringingabout remission of the disease, but the exactreasons for the success of this “differentia-tion therapy” are not fully understood. Unfor-tunately some patients react badly to high-dose treatment with all-trans RA and somebecome resistant.

Carotenoids and chronicdiseases

There is a great deal of evidence to show thatserum levels of β-carotene are lower thanusual in many disease states. It has usuallybeen assumed that this indication of whatmight be called low “β-carotene status” is anadverse effect and if corrected should lead tosome health benefit. Surprise has been ex-pressed that β-carotene supplementationunder some circumstances, such as in ciga-rette smokers with lung cancer, has been re-lated to deterioration rather than benefit (Theα-Tocopherol, β-Carotene Cancer Prevention

Figure 10.1 Formulae of some highly active syn-thetic retinoids.


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Study Group, 1994; Omenn, Goodman,Thornquist et al, 1996). The hypothesis hasrecently been put forward (Jandacek, 2000)that low β-carotene reflects the result of dis-ease, serves as an indicator of the presenceof disease, and is in no way causally related.This might be an explanation of some of theanomalous results that have been obtained,but much more work needs to be done.

On the other hand it has been suggested,on the basis of work in experimental animals,that abnormal oxidation products of β-caro-tene might be responsible for the adverseeffects of large doses mentioned above. Un-til recently it has always been assumed thathypercarotenosis had no harmful effects butonly caused high blood levels and pigmenta-tion of the skin. It seems that there is still a lotto learn about both the safety as well as thebenefits of carotenoid ingestion.

The skin

Erythropoietic porphyria is an uncommon dis-order of porphyrin metabolism in which a se-vere dermatosis may affect areas of the skinexposed to sunlight. The regular ingestion ofvery high levels of β-carotene leads tohypercarotenosis in which the blood level ishigh and deposition occurs in the skin. Thiswas shown to be protective in this diseaseand the recommended dose is about 180 mgper day.

The eye

In Chapter 1 it was mentioned that carot-enoids commonly accumulate in various tis-sues and certain carotenoids appear to havea predilection for certain tissues. β-carotenepreferentially accumulates in the human ovarybut the significance of this is unclear. In pri-mates there is a specific uptake of twononprovitamin A carotenoids, lutein and ze-axanthin, from the diet by the macula regionof the retina. This accounts for the yellow

colour of the macula which is the site of maxi-mal visual acuity (Harnois, Samson,Malenfaut et al, 1989; Demmig-Adams,Gilmore, Adams III, 1996).

Age-related macular degeneration (AMD)is a disease, or group of diseases, that causesa devastating loss of vision in the elderly. It isthe commonest cause of blindness in the over75 years age group. The cause is unknownbut there is now intensive research going on,both epidemiological and clinical, in which itis hypothesized that diet plays a part. Dietaryintake of lutein and zeaxanthin, the twomacula pigments, does not appear to be re-lated and there is some evidence that anothercarotenoid, lycopene, in high concentrationin tomatoes, may be protective. Other nutri-ents such as zinc and some antioxidants maybe involved (Taylor, 1999; Schalch, 2000).

Cataract, which consists of a gradual opaci-fication of the lens of the eye leading eventu-ally to blindness, has hitherto only been ca-pable of treatment by removal of the dam-aged lens. On the basis that oxidative dam-age may be responsible the possible asso-ciation of dietary intake of antioxidant nutri-ents, like the carotenoids, and vitamins C andE is being studied. As in the case of AMD thereis no conclusive evidence either way atpresent (Taylor, 1999). A recent study ofmonozygotic and dizygotic twins in the UKshowed that almost 50% of the variation inseverity of nuclear cataract could be ex-plained by heredity, about 38% by age andonly 14% by environment (Hammond,Snieder, Spector et al, 2000). In other partsof the world where nutritional deficiencies andother environmental factors are very differ-ent, results might also be very different.

Cancer

As was the case with vitamin A (see above)so with the carotenoids the types of cancerthat appear to be most closely related to


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carotenoid intake are those of epithelial cellorigin – lung, head and neck, oesophagus andstomach, colorectal, breast, cervix, and pros-tate cancers. β-carotene has been most stud-ied, but in the case of prostate cancerlycopene appears to be most promising. Tri-als of β-carotene supplementation in high-riskgroups like asbestos workers and cigarettesmokers have given unexpected results thatshowed either negative or even adverse ef-fects of supplementation. It is generally con-cluded that supplementation with specificnutrients, especially in large doses, is notadvisable. Increased intake of fruit and veg-etables provides a variety of antioxidant andother beneficial substances (Orfanos, Braun-Falco, Farber et al, 1981).

Cardiovascular disease

The results of numerous epidemiological stud-ies involving β-carotene and other micro-nutrients in relation to the occurrence of is-chaemic heart disease are conflicting. A pos-sible mechanism – if there is an effect – isreduced oxidation of low density lipoproteins,which seem to play a part in atherogenesis.Other carotenoids rather than β-carotene it-self may be effective but a great deal moreresearch is required in this and other relatedareas touched on here.


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IntroductionAt the World Summit for Children in 1990 andat the International Conference on Nutritionin 1992 the goal agreed upon was to “virtu-ally eliminate vitamin A deficiency and all itsconsequences including blindness by the year2000”. 1995 passed without the mid-decadegoal of “ensuring that at least 80% of chil-dren under 24 months of age receive ad-equate vitamin A through a combination ofstrategies” being met. In the first edition it wasnoted that “ With very little time remaining thegoal for the year 2000 is most unlikely to bereached in its entirety”. At that time the latestfigures (Underwood, 1996) suggested thatclinical xerophthalmia had diminished to a fig-ure of about 3 million annually. The prevalenceof subclinical deficiency was estimated to haverisen to about 230 million. Data are still un-available from a number of countries and thesefigures are likely to be a considerable under-estimation (see Chapter 8).

Among the criticisms that were levelled atthe first edition of the Manual one recurredmuch more frequently than any other. Thiswas that the chapter on Control should beexpanded considerably in any later version.This point has been well taken and what fol-lows is meant to satisfy this need.

There are several distinct types of interven-tion designed to lead to the control of VADDand these will be briefly introduced before theyare considered at greater length later.

Treatment

For the forseeable future control of clinicalVAD will include treatment of establishedcases in hospitals and clinics. Central to thisprocess is the administration of high-dosevitamin A preparations as capsules or in otherforms. Provision of a regular supply of vita-min A in these forms where they are neededhas yet to be achieved in vast areas of theworld where VADD are a serious public healthproblem. In addition to provision on a routinebasis of vitamin A preparations, there is wide-spread need for training in the recognition ofthe various stages of VADD and in simplemeasures for preventing recurrence of theproblem. Achievement of even these modestgoals is an important part of control. In re-cent years it has been recognized that chil-dren with subclinical deficiency have an in-creased risk of dying. Many of these havesevere measles, diarrhoea, and/or PEM andhave been recommended in the past for whathas been termed “targeted prevention” withvitamin A supplementation. In these circum-stances they should be considered to be sub-jects of treatment which includes vitamin A.

Prophylaxis

Periodic high-dose vitamin A distribution orsupplementation in the community may beviewed as a prophylactic extension of treat-ment in hospital. The form of vitamin A is usu-ally the same – capsules. The aim here isshort-term prevention. The measure, like


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treatment of the established case, is an emer-gency one, to be superseded or supple-mented by something of longer-term effect assoon as possible.

Control of infections

In recent years the close two-way associa-tion between VADD and infectious diseaseshas become well recognized (see Chapters6 and 9). This has led to the view that thecombination of vitamin A supplementation withimmunization has distinct theoretical andpractical advantages. In recent years thiscombined approach has been tested andfound not to have important adverse effects.The promotion of National Immunization Days(NIDs) by many countries has provided anovel opportunity for vitamin A supplementa-tion of young children on a large scale. Thisand other aspects of the subject are dis-cussed further below.

Food fortification

Food fortification has a long history, startingin industrialized countries and spreading morerecently to developing countries. It is argu-ably justified to add nutrients to widely con-sumed foodstuffs if vulnerable groups areunlikely to obtain their nutrient requirementsin any other way. Certain conditions need tobe met if a programme is to be successfullysustained. In the past few years this form ofVAD control has grown considerably andrecently multimicronutrient fortification hasbeen introduced.

Dietary interventions

Dietary interventions of various kinds wouldseem to be the logical approach to the prob-lem in most circumstances. For those whoapproach the problem for the first time it isusually a surprise and a shock to learn thatthe vast majority of young children going blindand dying with vitamin A deficiency do so sur-

rounded by readily available sources of thevitamin. There are indeed “many slips be-tween cup and lip”: problems in getting thevitamin out of the food and into the child. Theevidence produced in recent years that thebioavailability of provitamin A carotenoidsfrom fruit and vegetables is usually less thanpreviously thought (Chapter 2) has tended toincrease the difficulties of VAD control bymeans of dietary improvement. As a conse-quence, greater emphasis is being placed onthe value of promoting the much more read-ily bioavailable preformed vitamin A sourceswherever this is feasible.

New plants

Plant breeding and genetic modification: Veryrecently plant breeding has been applied tothe development of a number of high-caro-tene foods. The genetic modification of riceto provide β-carotene has attracted worldwideattention and requires careful considerationin relation to the control of VADD.

Disaster relief

Disaster relief victims of natural and man-made disasters are especially susceptible tohunger and malnutrition. In these unnaturaland emergency situations it is important thatthose who take on their care are able to pro-vide an adequate and balanced diet.

General considerationsIn a recent report by the Administrative Com-mittee on Coordination, Subcommittee onNutrition (ACC/SCN Consultative Group,1994) on Controlling Vitamin A Deficiencyresults were reported of a comparative evalu-ation of different interventions, drawing on 46individual evaluations. 25 were of supplemen-tation interventions (vitamin A dosing), 13 ofdietary modification, 4 of fortification, 2 ofpublic health, and 2 of breast-feeding. Sup-plementation is easiest to implement and to

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evaluate. It is difficult to make valid compari-sons between the different types of interven-tion. In addition to this it should be realizedthat some studies have been carried out un-der carefully controlled research conditionswhile others have been of a more routinenature. What goes on in strictly routine pro-grammes is very unlikely to be reported in thescientific literature.

In practice choices will need to be made atthe local level between the various controlmeasures on offer that have been outlinedabove. Wherever possible this choice shouldbe made after the situation has been as-sessed in some way (see Table 8.2). A base-line may then be established and the efficacyof measures introduced evaluated to someextent. Treatment of cases and prophylaxisfor vulnerable groups can be instituted almostright away. Other measures take much longerto be implemented fully. However, it shouldalways be possible to start some nutrition andhealth education pari passu with capsule use.

It is important to bear in mind that interven-tions of this nature are taking place in a situ-ation that can never be fully characterized andthat is constantly undergoing change. Itshould therefore be evident that it will rarelybe possible to attribute any benefit observeddirectly to the intervention. Good examplesof this are provided by the improvements thathave been documented in Bangladesh, Indiaand Indonesia (see Figure 8.8).

The wider implications of health interven-tions should be constantly at the back of theminds of those engaged in the control ofVADD and others like them. If health is to bea sustainable state (King, 1990) then in cir-cumstances where communities have out-grown, or are in the process of outgrowing,the carrying capacity of their ecosystem theethical implications of applying effective healthinterventions like vitamin A supplementationshould not be shirked (King, Elliott, 1993).

Finally, it may be helpful to point out thatthe SIGHT AND LIFE Newsletter regularlyprovides examples of what is going on allaround the world with regard to the routinecombat of VADD. We hope that some read-ers may be encouraged by reading aboutsome of these accounts to “have a go” them-selves.

TreatmentOn several occasions WHO has made rec-ommendations for the treatment of xeroph-thalmia. The latest schedule is shown in Ta-ble 11.1.

Retinyl palmitate in oily solution (as con-tained in capsules) by mouth is the preferredform and route of administration. The full dos-ing schedule should be given for all stages ofclinical xerophthalmia, not just for the moresevere. This should also apply to those eligi-ble for what was termed “targeted prevention”referred to above.

In rare cases where there is persistent vom-iting or severe diarrhoea that might preventingestion and absorption of the vitamin, in-tramuscular water-miscible vitamin A may begiven. Recently, an aerosol of retinyl palmi-tate for inhalation has been successfully fieldtested in preschool children in Ethiopia(Biesalski, Reifen, Fürst et al, 1999). Vitamin Awas well absorbed through the respiratorytract and might be preferable to injection.

Because of the known teratogenic effectsof large doses of vitamin A, care has to beexercised in the treatment of xerophthalmiain pregnant women. Active corneal lesionsshould receive the full treatment, but XN andX1B are treated with 10,000 IU (3.0 mg reti-nol, see Table 11.1) daily for two weeks(WHO, UNICEF, IVACG Task Force, 1988).

Associated medical conditions, such asPEM, measles, diarrhoea, should receive


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appropriate treatment. Frequently, secondaryinfections of the eye are also present andshould receive local and/or systemic treat-ment.

ProphylaxisChildren under the age of 6 years and preg-nant and lactating women constitute the mainvulnerable groups in communities where VADhas been identified as a public health problem.They should participate in a supplementationprogramme wherever this is deemed to be ap-propriate (see Table 11.2).

A number of studies carried out recently inseveral developing countries have shed ad-ditional light on some aspects of vitamin Asupplementation programmes. In Nepal(Christian, Schulze, Stoltzfus et al, 1998) sup-plementation with weekly dosage of vitaminA or β-carotene at about the RDA level failedto eliminate maternal night blindness in about60%. It is possible that some other factor be-sides vitamin A may also play a part, such as

deficiency of zinc (see Chapter 7). In a simi-lar study in Bangladesh (Rice, Stoltzfus, deFrancisco et al, 1999) vitamin A or β-carotenefailed to prevent subclinical vitamin A defi-ciency in lactating mothers and their infants.Universal distribution of vitamin A capsulesin Bangladesh was reviewed (Bloem, Hye,Wijnroks et al, 1995) and was shown to bean effective strategy for reducing night blind-ness incidence, but weaknesses were re-vealed in the rural areas of the programme.

There are two main areas of concern withregard to the safety of use of vitamin A prophy-laxis (Sommer, West, 1996, pp 394-399). Thefirst of these relates to acute adverse effectsin children. Nausea, vomiting and headachehave been reported in several per cent ofchildren taking part in large-dose programmes(30, 60 mg vitamin A). Severe vomiting (1.2%)was limited to the children given 60 mg vita-min A; symptoms lasted for almost all nolonger than 12–24 hours. In young infantsthere may also be observed bulging of theanterior fontanelle of the skull, which is still

Table 11.1. Treatment schedule for xerophthalmia for all age groups except women ofreproductive agea (WHO, UNICEF, IVACG Task Force, 1997)

Timing Vitamin A dosageb

Immediately on diagnosis:<6 months of age 50,000 IU6–12 months of age 100,000 IU>12 months of agea 200,000 IU

Next day Same age-specific dosec

At least 2 weeks later Same age-specific dosed

a Caution: Women of reproductive age with night blindness or Bitot's spots should receive daily doses≤10,000 IU, or weekly doses of ≤25,000 IU. However, all women of reproductive age, whether or notpregnant, who exhibit severe signs of active xerophthalmia (i.e. acute corneal lesions) should betreated as above.

b For oral administration, preferably in an oil-based preparation.c The mother or another responsible person can administer the next-day dose at home.d To be administered at a subsequent health-service contact with the indivldual.


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open at that age. Like the other symptomsthe effect is transient and there is no evidenceof after-effects (de Francisco, Chakraboty,Chowdhury et al, 1993). Several controlledtrials have been carried out and the consen-sus is that the extremely slight risk is fully jus-tified in view of the potential benefit to life andhealth (Florentino, Tanchoco, Ramos et al,1990). The effects of neonatal vitamin A sup-plementation was followed over a period ofmany months and no evidence was found foran adverse effect on development or growth(van Dillen, de Francisco, Wouterina et al,1996; Humphrey, Agoestina, Juliana et al,1998).

A very recent review of the vitamin A sup-plementation of young infants (Humphrey,Rice, 2000) concludes that “a regimen inwhich mothers are given 200,000 IU vitamin Aat delivery and their infants receive four dosesof 50,000 IU (i.e. at birth and with their immu-nization contacts) would allow nearly all in-fants to enter the second half of infancy inadequate vitamin A status”.

The second issue concerns vitamin Aprophylaxis during and shortly after preg-nancy. Vitamin A and related compounds inlarge doses are known to be teratogenic inearly pregnancy (Nau, Chahoud, Dencker etal, 1994). High-dose vitamin A given at orshortly after delivery has been shown to raisebreast milk levels considerably for a numberof months. Frequently this is a rare opportu-nity to apply prophylaxis. Present recommen-dations are that the high-dose prophylaxis(200,000 IU) would be given only to breast-feeding women at delivery or during the in-fertile postpartum period, currently thought tolast 4–6 weeks. IVACG (1998a) has issued astatement on “Safe doses of vitamin A duringpregnancy and lactation”.

WHO currently recommends that the rela-tively small increased need for vitamin A dur-ing pregnancy be met by diet, or a supple-ment not exceeding 10,000 IU daily through-out gestation (WHO, UNICEF, IVACG TaskForce 1997). This is a second edition of itsguide to the use of vitamin A supplements and

Table 11.2. High-dose universal-distribution schedule for prevention of vitamin Adeficiency (WHO, UNICEF, IVACG Task Force 1997)

Infants <6 months of agea

Non-breast-fed infants 50,000 IU orallyBreast-fed infants whose 50,000 lU orallymothers have not receivedsupplemental vitamin A

Infants 6–12 months of age 100,000 lU orally, every 4–6 monthsb

Children >12 months of age 200,000 IU orally, every 4–6 monthsb

Mothers 200,000 IU orally, within 8 weeks of delivery

a Programmes should ensure that infants <6 months of age do not receive the larger dose intended formothers. It may therefore be preferable to dose infants with a liquid dispenser to avoid possibleconfusion between capsules of different dosages.

b Evidence suggests that vitamin A reserves in deficient individuals can fall below optimal levels 3–6months following a high dose; however, dosing at 4–6 months intervals should be sufficient to pre-vent serious consequences of vitamin A deficiency.


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prevention of vitamin A deficiency and xeroph-thalmia. This was followed in by recommen-dations and a report of a consultation on “Safevitamin A dosage during pregnancy and lac-tation” (WHO, 1998).

As mentioned above, supplementationdoes not address the underlying cause(s) andis an emergency measure. It should beaccompanied by dietary counselling. Re-search studies (Sommer, West, 1996, pp 388-409) have shown that full implementation ofthe schedule is very efficacious. However,experience has shown that once a supple-mentation programme has been integratedinto the routine primary healthcare systemefficiency tends to fall to unacceptably lowlevels (West, Sommer, 1984). As was notedpreviously (see Chapter 6) those who are notcovered in the first place or who drop out sub-sequently are usually those in greatest needof the service.

Targeted distribution offers the greatest flex-ibility and cost-effectiveness and best utilizesexisting contacts between health providersand the community. This requires planning,coordination and needs to be sustained if theresults are to be better than those that comefrom passive targeting of only those childrenwho attend health clinics.

Universal distribution requires dosing of allchildren of the vulnerable age group in a high-risk area, usually on a semi-annual basis. Itis particularly this type of distribution that of-ten suffers from low coverage, as mentionedabove, due to all kinds of logistic problems.

Prevention and managementof infectious diseases

Attention was drawn earlier to the inter-rela-tionships of infections and vitamin A status(see Chapters 6 and 9) that need to be takeninto account in the control of VADD. Immuni-

zations that have been developed for certaininfectious diseases, especially measles, maybe seen as providing an opportunity for a jointapproach. The Expanded Programme onImmunization (EPI) of WHO advises that “anyEPI contact after the age of six months isappropriate for supplementing the infant oryoung child (with vitamin A). The visit formeasles vaccine at around 9–11 months isespecially suitable” (WHO, 1994).

It has been demonstrated on a number ofoccasions that integration of vitamin A sup-plementation into a successful immunizationprogramme, like EPI, can result in greatly in-creased coverage (Karim, Shahjahan, Begumet al, 1996). There is evidence that immuni-zation against measles is already having afavourable impact on reducing corneal blind-ness in young children. High-dose vitamin Awas shown to interfere to some extent withseroconversion to measles (Semba, Munasir,Beeler et al, 1995). Subsequent studies havefailed to confirm these initial concerns formeasles (Benn, Aaby, Balé et al, 1997), DPT(van Dillen, de Francisco, Overweg-Plandsoen, 1996) or polio (Semba, Muhilal,Mohgaddam et al, 1999). A large study inGhana, India and Peru with DPT, polio andmeasles immunization (WHO/CHD Immuni-zation-Linked Vitamin A SupplementationStudy Group, 1998) confirmed the safety ofthe intervention. Unfortunately it failed to findany sustained benefits in terms of vitamin Astatus beyond the age of 6 months or of in-fant morbidity.

It was reported at the XIX Meeting of IVACGin Durban (1999) that of the 64 countries thatcarried out National Immunization Days(NIDs) in 1998 43 or 67% added vitamin Adistribution to one of the immunization days.Thirteen more countries were planning to addvitamin A supplementation to their NIDs in1999. Reports of a number of successful suchprogrammes were presented at the meeting.As NIDs are being phased out since polio-


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myelitis is being eradicated there is urgentneed for other effective ways to increase vi-tamin A supplementation coverage, such asintensified measles and other infectious dis-ease immunization campaigns.

Food fortificationIn industrialized countries food fortification haslong been an accepted strategy for improv-ing micronutrient nutriture, including that ofvitamin A. In Denmark, during World War I,an epidemic of xerophthalmia paralleled thesubstitution of butter by margarine, whichlacked vitamin A. Today, margarine, is amongthose food items most frequently fortified withvitamin A in the world.

Potentially, food fortification offers a direct,effective and sustainable way to correct VAD.However, in practice it has sometimes proveddifficult to meet all the necessary criteria. Inthe early efforts to fortify staple foods techno-logical obstacles had to be overcome. Todaysuch problems are not considered to be limit-ing factors. Although technologically possible,implementation of food fortification has provedto be a complicated and long lasting process.

A food item to be fortified should be con-sumed regularly by most of the target popu-lation in certain quantities. There should beno risk of overdosing for those consuming thehighest quantities. Further criteria are that thevitamin A should not affect the appearance,colour, texture, or organoleptic properties ofthe food in order to be acceptable to the con-sumer. The stability of the vitamin A shouldremain at an acceptable level during pro-cessing, transport, storage and cooking.

It is evident that fortification is only possi-ble if processing of the food in question is tosome extent centralized. This is also neces-sary in order for adequate quality control tobe provided. Difficulties have to be overcomein relation to such matters as the passing and

implementation of food laws and regulationsand their continuing enforcement. The long-term financing of all the costs involved in for-tification has proved to be a stumbling blockin some programmes.

Like supplementation, food fortification maybe universal or targeted. In the former, fortifi-cation is applied throughout the population.In the latter it applies to specific groups, e.g.to supplementary feeding programmes forpregnant women, welfare recipients, schoolchildren, or those receiving complementaryfoods. Fortification of food aid is an importantissue (see p 134). Several research studies(Sommer, West, 1996, pp 410-430) havedemonstrated conclusively that fortificationcan significantly improve vitamin A status ofa whole population.

In developing countries many foods havebeen fortified with vitamin A or imported asfortified products. These include wheat, riceand other grain products, tea, dairy foods (es-pecially dried skim milk), margarine, edibleoils, formula foods and speciality items.

Sugar in Latin America and monosodiumglutamate (MSG, a popular flavour enhancer)in South-East Asia were the first vehicles forvitamin A fortification to be extensively tested,widely distributed and evaluated for their pub-lic health impact (Sommer, West, 1996, pp411-425). Neither of these food substancesis an ideal vehicle from the nutritional point ofview, but even so sugar fortification is in op-eration at the present time in several coun-tries in Central America and is in the processof being introduced in some countries in LatinAmerica and in Africa.

From the early 1970s fortification of white,refined sugar with vitamin A was proceededwithin a number of Central and South Ameri-can countries, with much of the developmenttaking place in Guatemala. Surveillance overa number of years demonstrated a positive


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impact of the programme (Arroyave, 1986).Adverse internal and external circumstanceshalted the programme for nearly eight years.In 1988, six months after a programme re-start there was significant reduction in thenumber of children with low serum retinol(26% to 10%) and of those with an abnormalRDR (33% to 14%) (Pineda, 1993).

In the 1970s, fortification of MSG was pur-sued in the Philippines and in Indonesia. Theprogrammes proved to be efficacious in chil-dren to raise serum retinol levels, reduce theprevalence of xerophthalmia, improve lineargrowth, and reduce mortality (Solon, Latham,Guirriec et al, 1985; Muhilal, Permaesih,Idjradinata et al, 1988) (Figure 11.1). Afternearly twenty years of research and devel-opment in both countries, MSG fortificationwith vitamin A has not been implemented.

As consequences of the greatly increasedinterest in micronutrient fortification of foodsin developing countries in recent years sev-

eral trends have become evident that arelikely to pose difficulties in the near future.Multimicronutrient fortification is rapidly on theincrease. For example, biscuits for primaryschool children in South Africa are being for-tified with iron, iodine, and β-carotene (vanStuijvenberg, Kvalsvig, Faber et al, 1999). Theevaluation of the effects of such studies andcomparison of results from different studiesis a complex matter. In some countries thereare now more than 20 different food itemsfortified with vitamin A at a high level, posingpossible problems of excess intake (IVACG,1999, p 54). One study from Guatemala(Krause, Delisle, Solomons, 1998) showedthat poor urban toddlers were obtaining abouthalf their recommended vitamin A intake fromfortified foods. Some evidence from CentralAmerica suggests that even prolonged forti-fication of a single food item may not havebeen sufficient to make a lasting impact on aproblem of VAD there (IVACG, 1999, p 54). Itis being suggested that fortification and sup-plementation may both be required.

Figure 11.1. Effect of MSG (monosodium glutamate) fortification (Muhilal,Permaesih, Idjradinata et al, 1988).


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Despite the limitations and the drawbacksthe examples given here have demonstratedthat food fortification can be a very powerfulstrategy. In order for food fortification to besuccessful, effective collaboration of all par-ties involved, including scientists, industry,public advocacy groups, legislators and politi-cians, is essential. Sommer and West (1996,pp 410-430) end their review of the subject“...implementing a national fortification pro-gram is a major undertaking that requiressound scientific rationale, industrial capacity,training, advocacy, adequate legislative sup-port, economic viability, community accept-ance and long-term sustainability, monitoringand quality control”.

Dietary modificationThe ACC/SCN Consultative Group (1994)pointed out that there are four types of strat-egies aimed at achieving the goal of dietarymodification:

1) Nutrition education or communication, of-ten using a social marketing approach, toimprove practices related to the consump-tion of available vitamin A-rich foodsources.

2) Horticultural interventions (or home foodprovisioning), e.g. home gardening, thataim to increase availability of vitamin A-richfoods.

3) Economic/food policies affecting availabil-ity, price and effective demand of vitaminA-rich foods.

4) Technological advances concerning foodpreservation, plant breeding etc.

Strategies 2–4 aim to improve the availabilityof vitamin A-rich foods. Strategy 1 aims toimprove their consumption.

The report goes on to review 13 dietarymodification evaluations. Nine of these incor-porated some education/communicationproject activities, 7 included home gardening(4 of which were combined with social mar-keting activities), and one study examinedchanges in consumption in response to natu-rally occurring changes in prices and availabil-ity of vitamin A-rich foods. Most of the evalua-tions were of pilot projects or field trials.

It was possible to demonstrate positivechange, to varying degrees in severalprojects. These included improvements inknowledge, attitude and practices (KAP) inNorth-East Thailand (Smitasiri, Attig,Dhanamitta, 1992) and West Sumatra (Pol-lard, van der Pasch, 1990). In Bangladeshthere was a 40–60% increase in productionand consumption by young children of greenleafy vegetables and yellow fruits. There wasincreased awareness of night blindness andprevalence fell (Institute of Nutrition and FoodScience, Bangladesh, 1990). However, docu-mentation of the extent of improvement com-parable to the documentation of the efficacy offortification or capsule programmes is lacking.

In general it appears that consumption ofmore than 40% of total vitamin A in the formof preformed vitamin A is highly protective(FAO/WHO Expert Consultation, 1988).

Dietary interventions are usually targetedtowards vulnerable groups – infants, pre-school age children and their pregnant andlactating mothers. School age children mightalso be included if shown to be particularly atrisk. The food categories to be promoted willvary with the vulnerable group (Figure 11.2).

Surveys have shown that young childrenfrequently eat less than 15 g of green leafyvegetables in a day. It was shown in Bangla-desh (Rahman, Mahalanabis, Islam et al,1993) that 40 g of dark green leaves wouldbe readily consumed daily if prepared attrac-


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Figure 11.2. Composite profile of age-specific protection against xerophthalmia and low serum retinollevels conferred by dietary intakes of selected types of foods. Solid bar denotes ages for which epide-miologic evidence is strong. Dashed bar denotes ages at which some evidence of protection exists fora food (Sommer, West, 1996, pp 130-137).

tively. This is sufficient to provide the dailyrequirement of vitamin A in one meal.

Most yellow fruits and some green leavesare usually available only at certain seasons.Village-based food processing and pres-ervation can extend the availability and ac-ceptability (Sommer, West, 1996, pp 355-387).

In dietary interventions, more so than inother kinds, it is of special importance to takeinto account the efficacy or effectiveness ofthe intervention. An intervention is effective ifit can be shown to have produced the desiredeffect; in this case to have improved vitaminA nutriture. Consequently, to have increasedthe vitamin A (usually provitamin A) intakedoes not satisfy this criterion. Improving vita-min A status (measured by serum retinol orsome other method) may be considered tohave done so.

Recent work suggests that provitamin Acarotenoids, in their natural form in foods, arenot as effective as has often been assumedin the past (de Pee, West, Muhilal et al, 1995;Bulux, Quan de Serrano, Giuliano, 1994). Thenature of the matrix may be important andsome diets of vulnerable communities are lowin fat. Dietary fat appears to be more impor-tant for the absorption of carotene than forthat of preformed vitamin A. More attention isnow being given to encouraging even a smallincrease in preformed vitamin A intake fromsuch readily available sources as eggs andperhaps milk or fortified foods.

Dietary modification can be brought aboutby a variety of means, and if several can beemployed so much the better. In Vietnam(English, Badcock, Giay et al 1997) homegarden production and nutrition educationwere combined and highly significant improve-


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ment in the incidence of diarrhoeal diseaseand respiratory infections (but see p 77)resulted. Social marketing of vitamin A -richfoods in Thailand to bring about behaviouralchange, with especial emphasis of use of thereadily available ivy gourd, could be readilyapplied in the region (Smitasiri, Attig,Valyasevi et al 1993). The XIX Meeting ofIVACG (see p 55) reviewed a series of paperspresented at the meeting on experiences with“communicating micronutrients to the public”.

With recent concerns being expressedabout the bioavailability of provitamin Acarotenoids (see Chapter 2) renewed inter-est has been aroused in red palm oil as apotent source of vitamin A (Mahapatra,Manorama, 1997; Solomons, 1998). There isurgent need for more thorough assessmentof the value of this and other palm productsas underexploited sources of the vitamin.

General issues

Multiple strategies are now being increasinglyemployed and “sorting out the wood from thetrees” is becoming increasingly difficult. TheProceedings of the XIX Meeting of IVACGonce again has come to the rescue (IVACG1999, pp 57-61) with a three-page table andaccompanying text.

Cost-effectiveness has always been animportant issue but is only recently being ad-dressed by well-designed and executed stud-ies. Targeting vitamin A supplements to high-risk children was found not to be an efficientuse of resources. It was concluded that, likeimmunization, vitamin A should be providedto all preschool age children in developingcountries (Loevinsohn, Sutter, Costales,1997). In a comparison of nutrition educationand vitamin A supplementation it was foundthat the latter was quicker and cheaper, buteducation had longer lasting effects. It wasconcluded that both were needed for a com-prehensive national programme (Pant,

Pokharel, Curtale et al, 1996). Under idealcircumstances vitamin A fortification can becheaper and more efficient than either cap-sule distribution or home food production withnutrition education (Phillips, Sanghvi, Suaréz,1996).

Plant breeding and geneticmodification

Traditional methods of plant breeding havebeen applied quite extensively to the en-hancement of the β-carotene content of foodssince this topic was raised in the first editionof the Manual (Bouis, 1996). These includehigher-yielding varieties of amaranth in India,tomatoes with a high β-carotene content inTaiwan, high-carotene sweet potato in Africa,and red canola oil with a unique blend of sev-eral carotenoids (Reddy, 2000).

Genetically modified (GM) rice, aimed at im-proving the supply of iron and vitamin A inthe human diet was first announced at theXVI International Botanical Congress on 3August 1999. The definitive publication of thisground-breaking research was made a fewmonths later (Ye, Al-Babali, Klöti et al, 2000).The research involved collaboration betweenthe Institute for Plant Sciences of the SwissFederal Institute of Technology, Zurich, Swit-zerland and the Center for AppliedBiosciences of the University of Freiburg, Frei-burg, Germany.

Rice (Oryza sativa) is usually milled to re-move the oil-rich aleurone layer that turnsrancid upon storage especially in tropical ar-eas. This layer contains some β-carotene andsome other nutrients which do not occur inthe remaining edible portion of the grain, theendosperm. In this research recombinantDNA technology, with a combination oftransgenes, was used to enable biosynthe-sis of provitamin A in the endosperm to oc-cur. Immature rice endosperm can synthesize


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the early intermediate geranylgeranyl-diphosphate (GGPP – see also Chapter 1).This can be used to produce the uncolouredcarotene phytoene by expressing the enzymephytoene synthase in rice endosperm. For thesynthetic pathway to be completed towardsβ-carotene three additional plant enzymes arerequired – phytoene desaturase and ζ-caro-tene desaturase, each of which catalyzes theintroduction of two double bonds, andlycopene β-cyclase, encoded by the lcygene. Four transgenes were required; allwere obtained from daffodil (Narcissuspseudonarcissus).

In most cases the transformed endospermsof the rice were yellow in colour, indicatingthe formation of carotenoid. There was somevariation in different seed lines concerning thecarotenoids produced. Often this was only β-carotene, but occasionally lutein and zeax-anthin were also detected. From the resultsso far it seems that the yield of provitamin Awill be at least 2 µg/g of rice as consumed.The authors suggest that a daily intake of300 g of rice will provide 100 µg RE. Thiswould be equivalent to about 25% of theadult’s RDA. This assumes that thebioavailability of β-carotene would be 1/6 thatof retinol, but this remains to be proved.

There are still many technological, socio-logical and other considerations to be ad-dressed before there is any possibility of GMrice becoming the staple food of hundreds ofmillions of the world’s poor. A diet of ordinaryrice adequately supplemented with vegeta-bles and fruits is capable of providing a bal-anced supply of known nutrients and otherhealth-promoting substances. The overridinggoal of attaining full nutrition for all by prac-tical and realistic means should not be allowedto be obscured by any “quick fix” approaches.

Disaster reliefOver the past two decades the number ofrefugees registered by the UN High Commis-sion has risen steadily and now approximates20 million. In addition, the estimated numberof people forced from their homes but not fromtheir countries is now nearly 30 million. Abouthalf of these groups are children under theage of 15 years and are especially vulner-able. Experience has shown that they are notonly particularly susceptible to infections andprotein-energy malnutrition but also to vita-min A and other vitamin deficiencies(McLaren, 1987).

If agencies involved in disaster relief op-erations are made aware of the problem, thereis no reason why it should not be averted. Itshould be ensured that the vitamin A contentof food rations supplied is adequate. In par-ticular skim milk must be fortified, as it usu-ally is, with vitamin A. The most readily im-plemented single measure is the distributionof vitamin A capsules to all young children.Mothers should be encouraged to breast-feedtheir infants. In more settled circumstancesthe growing of green leaves and yellow fruitsshould be encouraged.

Some country experiencesThese are a few examples of the reports thatappear regularly in SIGHT AND LIFE News-letter. They are not meant to be representa-tive in any way but were chosen because theywere seen to illustrate the variety of ap-proaches to the problem of the control ofVADD, some of the difficulties involved andthe attempts to overcome these. Earlier onmost of the accounts related to the problemof xerophthalmia and nutritional blindness.Although severe VAD has not yet been elimi-nated along with most other severe forms ofnutritional deficiency it has diminished consid-erably worldwide. The emphasis now needs


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to be placed on the much more widespreadsubclinical VAD that threatens survival andgeneral health. If this is successfully tackledxerophthalmia will automatically decrease.The reports have been condensed and it ishoped that readers will turn to the full accountsfor further information and also be encour-aged to follow other reports as they appearin future Newsletters.

Involving programme participants in theevaluation and replanning of how toreach the “ hard-to-reach group (HRG)”(Shamim, Ahmed, Costa et al, 1999)

This group found that the usual models advo-cated for homestead production of vegetablesand fruits, with 3–5 varieties of vegetables grownin raised beds in small plots were inappropriatefor local conditions in Debidwar, Bangladesh.Moreover, local people’s opinion in planningand implementing is usually not sought. Con-sequently a participatory rural appraisal (PRA)method was used. Focus group discussions,interviews, conversations, observations and dis-

cussions with key informants were held. Indig-enous technical knowledge about such mattersas traditional food plants, the growing of plantsin the homestead including use of the roof andutilization of by-products was collected. Suchcontacts, experience and knowledge formedthe basis for future programmes. This kind ofconfidence-building, partnership-forming ap-proach needs to be widely encouraged.

Figure 11.3. Production of beans on the roof of a hut. Year-round production of suchcrops could contribute to the nutrition.

Figure 11.4. Drumstick (Moringa oleifera): itslleaves, flowers and fruits are edible. It was iden-tified as a promising crop as it requires little care,is easy to grow and yields for many years.


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min A carotenoids. This account from Indiagives details of the equipment needed, theway the material may be prepared at home,either to feed domestic animals or to incor-porate into attractive meals that people arealready used to. A table is given showingtypical amounts in leaf concentrate of a va-riety of nutrients (β-carotene is 50–180 mg/100 g of dry matter). Several studies in In-dia and elsewhere have shown that β-caro-tene in leaf concentrate is well absorbed.Initial cost of the equipment and difficulty inobtaining spare parts are often quoted asbarriers to long-term operation of the pro-gramme.

Leaf concentrate: a good food source tocontrol vitamin A deficiency (Joshi 1998)

Leaf protein, as it was originally called by itsfounder N.W. Pirie in the 1950s, was devel-oped as an attempt to combat what was thentermed the “protein crisis”. For various rea-sons it became evident eventually that pro-tein deficiency was not the main cause ofmalnutrition in young children but a globallack of nutrients and energy sources com-bined with infections. As “leaf concentrate”the green curd prepared from species of leafnot commonly eaten as human food is mak-ing a comeback as a rich source of provita-

Figure 11.5. Snacks prepared with inclusion of leaf protein.

Figure 11.6. Camel market in Mao, Kanem Province.


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Figure 11.8. Milking a goat.

Towards improved health services fornomadic people in Chad: the challenge ofcombining human and animal health(Zinsstag, 2000)

About 10% of the 7 million population of thisdesert African country are nomads. They havevirtually no access to the public health sys-tem and their health status is unknown. Closecontact with animals means they are vulner-able to zoonotic diseases. Their diet consistsof more than 60% of milk and milk products,which should include ample vitamin A. Be-cause man here is so dependent upon hisdomestic animals a joint veterinary and hu-man medicine approach is being adopted withregard to control of diseases like tuberculo-sis and vaccination programmes which untilnow have been especially lacking on the hu-man side.

In time of drought, always imminent in suchdesertic environments, livestock and humansare equally badly hit and it is difficult to seehow their vitamin A and other nutritional needscan be met under these circumstances. Thenext experience may have an answer.

Vitamin A in milk from cows, goats andsheep related to β-carotene in fodder –Timbuktu, Mali (Jacks, 1997)

In northern Mali repeated drought over thelast two decades has decimated the herdsby up to 80%. Vitamin A deficiency is com-mon in mothers and children during the drysummer season. It was found that the β-caro-tene content in animal milk was closely re-lated to that of the fodder. Goat’s milk has thehighest β-carotene content and is customar-

Figure 11.7. A nomadic family south of N’Djaména.


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A food-based strategy to prevent vitaminA deficiency – the Vietnam experience.(Vuong, 2000)

It was decided to promote the use of the brightred Gac fruit (Momordica CochinchinnensisSpreng), rich in β-carotene, as a practical con-tribution towards the control of VADD in north-ern Vietnam. The seed membrane and pulpof the Gac fruit contains significant concen-trations of oil, which facilitates absorption. TheGac vine commonly grows at the entrance torural homes. Traditionally, Gac seed and pulpare mixed with cooked rice to give colour andflavour. Studies on the local children showedsignificant increases in serum retinol levelsin groups receiving the fruit. The local prepa-ration method of the fruit in meals causedminimal loss of β-carotene. At present the fruitis underutilized because of seasonality andlack of awareness of its value, but efforts arebeing made to overcome this. Such reports,like this and the one that follows, should en-courage others to look for the possibilities oflocal answers to their VAD problems.

ily used as a weaning food by the people.Woody fodder species suitable for the dry cli-mate, such as Maerua crassifolia, Salvadorapersica, and Balanites aegyptica are beingpromoted. The leaves of Maerua crassifoliahave good nutritional value even as humanfood. It is important that innovative experi-ences like this should be disseminated tothose in similar circumstances and that re-search not be unnecessarily duplicated.

Figure 11.9. Camel browsing on an Acacia tortilisand the Tuareg owner.

Figure 11.10. Schoolchildren with SIGHT AND LIFE posters.


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Figure 11.12. Schoolchildren bringing karat plants.

Promotion of vitamin A-rich foods inPohnpei, Federated States of Micronesia(Englberger, 1999)

In this case a once highly treasured traditionalweaning food has been revived. It came asrather a shock when these island peoplelearned in 1994 through a child health surveythat 51% of their children had low serum lev-els of retinol. In 1998 another surprise, butthis time a pleasant one, was the finding thatthe local karat banana (Musa Troglodytarum)is rich in vitamin A – 160 RE/100 g. A secondlocal banana, the mangat, was found to con-tain 96 RE/100 g. The writer goes on to de-scribe the programme undertaken to promotebanana consumption by competitions forgrowing, making posters, cooking demonstra-tions, the use of the media and the culmina-tion in a vitamin A campaign week.

Figure 11.11. Karat bananas fruiting straight intothe air.

Surveillance and intervention of vitaminA status of pre-school children in Fu Pingcounty, Baoding region, China (Wang,Zhan, Hua, et al, 2000)

Fu Ping county is a remote and mountainousarea where most of the over 200,000 inhabit-ants are farmers. Large numbers of men haveleft to find work in the cities, leaving womenand children behind. Water is scarce and themain crops are maize, oats, potatoes andChinese dates. VADD and iodine deficiencydisorders (IDD) are common. Serum retinollevels were measured in young children inboth Fu Ping and Lai Yuan counties. In bothareas a severe subclinical vitamin A deficiencyproblem was revealed for which preventivemeasures are being planned.

It is very gratifying to learn that now in themost populous country on earth a widespreadVAD problem is being suspected, assessmentof vitamin A status is being carried out andcontrol measures are being planned.


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Figure 11.15. Nursing mother weaving carpet.

Figure 11.14. Carpet weaving.

Elimination of vitamin A deficiencythrough active surveillance of carpetchildren north-east of Kathmandu(Chalise, 1998)

This report describes the work of Helpless Re-habilitation Society (HRS) among the carpetfactory workers, children <10 years of age andpregnant and lactating women in the north-east area of the Kathmandu Valley. Much ofthe country is now covered by the nationalvitamin A programme but these economic mi-grants from the ecological destruction in thehills miss out. After capsule distribution andpromotion of improved diet xerophthalmia ofall degrees in children fell from 13% to 1.5%.Factory owners proved very cooperative andothers are asking for similar help for the elimi-nation of a problem that was clearly imped-ing the efficiency of their workers. One is leftwondering about the dilemma of the immo-rality of child labour and with their originalhome environments destroyed by corporategreed what the alternative might be.

Figure 11.13. Children in the village Long Quan Guan waiting to receive a vitamin A supplement.


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ACC/SCN Consultative Group(1994).Controlling Vitamin A Deficiency. ACC/SCNState-of-the-art Series, Nutrition Policy Dis-cussion Paper no 14, United Nations, Geneva

This is an important, official review of con-trol of VADD, the subject of Chapter 11.

Arroyave G, Chichester CO, Flores H etal(1982). Biochemical Methodology for theAssessment of Vitamin A Status.IVACG, Nutri-tion Foundation, Washington, DC

A detailed review of methods of biochemi-cal analysis (Chapter 1) and of the assess-ment of vitamin A status (Chapter 4).

Bauernfeind JC (ed) (1981). Carotenoidsas Colorants and Vitamin A Precursors. Aca-demic Press, New York

A comprehensive, extensively referencedreview that covers topics dealt with here inChapters 1 and 11.

Bauernfeind JC (ed) (1986). Vitamin A De-ficiency and its Control. Academic Press, NewYork

All aspects of VADD covered in this Manualare dealt with here. It has to be rememberedthat considerable advances have been madein the intervening years. Chapter 18 of thisbook provides interesting information on or-ganizations involved in the eradication of vi-tamin A deficiency.

Beaton GH, Martorell R, Aronson KJ etal(1993). Effectiveness of Vitamin A Supple-mentation in the Control of Young Child Mor-

bidity and Mortality in DevelopingCountries.ACC/SCN State-of-the-art Series,Nutrition Policy Discussion Paper no 13,United Nations, Geneva

The most comprehensive of several meta-analyses.

Blomhoff R(ed)(1994). Vitamin A in Healthand Disease.Dekker, New York

The most extensive review of the subjectat the present time. It has particular value inrelation to basic biochemistry and molecularbiology of vitamin A (see Chapter 3).

Blomhoff R, Green MH, Green JB et al(1991). Vitamin A metabolism: new perspec-tives on absorption, transport, and storage.Physiol Rev 71:951-990

Blomhoff R, Green MH, Norum KR(1992). Vitamin A: physiological and bio-chemical processing. Ann Rev Nutr 12:37-60

These two reviews provide intensive cov-erage of Chapter 3 topics.

Britton G (1995). Structure and propertiesof carotenoids in relation to function. FASEBJ 9: 1551-8

Deals with basic physics and chemistry ofcarotenoids.

Burri BJ (2000). Carotenoids and gene ex-pression. Nutrition 16: 577-578. A look intothe future in this exciting field.

Further Reading


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Castenmiller JJM, West CE (1998).Bioavailability and bioconversion ofcarotenoids. Annu Rev Nutr 18: 19-38

Recent review of this rapidly expanding field.

Chytil F, Ong (1987). Intracellular vitaminA-binding proteins. Ann Rev Nutr 7:321-335

In-depth review by major contributors in thisfield.

Cox FEG (ed) (1996). Illustrated History ofTropical Diseases. Wellcome Trust, London

Includes an account of the history of vita-min A and vitamin A deficiency by DSMcLaren.

de Pee S (1996). Food-Based Approachesfor Controlling Vitamin A Deficiency: Studiesin Breastfeeding Women in Indonesia. the-sis, Wageningen University, Netherlands

FAO/WHO Expert Consultation (1988).Requirements of Vitamin A, Iron, Folate, andVitamin B12. Food and Nutrition Series no.23, FAO, Rome

The latest international report to considerrequirements for vitamin A.

Goodwin TW (1984). The Biochemistry ofthe Carotenoids, vols 1 and 2. Chapman andHall, London

Probably the most comprehensive recentreview of subjects relating mainly to Chapter 1.

Gopalan C, Narasinga Rao BS, SeshadriS (1992). Combating Vitamin A Deficiencythrough Dietary Improvement. Spec Publ Serno 6, Nutrition Foundation of India, New Delhi

Isler O (ed) (1971). Carotenoids. Birk-häuser, Basel

Classic account of carotenoids in nature.

Johnson GJ, Minassian DC, Weale R.(1998). The Epidemiology of Eye Disease.Chapman and Hall, London

This book, the first on the subject, contains

a chapter on “The Epidemiology of Vitamin ADeficiency Disorders (VADD)” by DSMcLaren.

Karrer P, Jucker E (1950). Carotenoids(translation by EA Braude). Elsevier, Amster-dam

Another classic account.

Krinsky NI (1989). Antioxidant functions ofcarotenoids. Free Rad Biol Med 7:617-632

Full account of functions of carotenoidstouched on in Chapter 3.

Livrea MA, Packer L (eds) (1992).Retinoids: Progress in Research and ClinicalApplications. Dekker, New York

Comprehensive review of basic aspects ofthe subject.

Machlin LJ (ed) (1991). Handbook of Vi-tamins, 2nd edition. Dekker, New York

Includes thorough general review of vita-min A by JA Olson.

McLaren DS (1980). Nutritional Ophthal-mology. Academic Press, London

Includes coverage of earlier literature onexperimental and human xerophthalmia.

McLaren DS (1999). Towards the Con-quest of Vitamin A Deficiency Disorders(VADD). Sight and Life, Basel

Largely biographical and historical accountof progress in the last century.

Moore T (1957). Vitamin A. Elsevier, Am-sterdam

The first book on vitamin A; it continues toprovide much information of contemporary aswell as historic interest.

Newman V (1993). Vitamin A andbreastfeeding: a comparison of data fromdeveloped and developing countries.Wellstart, San Diego


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Niles RM (2000). Vitamin A and Cancer.Nutrition 16:573-576.

A very recent account of this field.

Pfander H (1987). Key to Carotenoids, 2ndedition. Birkhduser, Basel

Comprehensive review of carotenoids.

Orfanos CE, Braun-Falco O, Faber EMet al (1981). Retinoids: Advances in Basic Re-search and Therapy . Springer-Verlag, Berlin

Porter JW, Spurgeon SL (eds) (1983).Biosynthesis of Isoprenoid Compounds, vols1 and 2. Wiley, New York

Contains one article on the formation andfunction of vitamin A by JA Olson.

Rodriguez-Amaya DB (1997).Carotenoids and Food Preparation. OmniProject, Washington DC

Rodriguez-Amaya DB (1999). A Guide toCarotenoid Analysis in Foods. OMNI Re-search, Washington, DC

Both monographs excellent sources of in-formation.

Roodenburg AJC (1996). Dietary vitaminA and iron metabolism in the rat.

Thesis University of Wageningen, Nether-lands. Includes extensive review of literatureon vitamin A and iron interactions.

Scrimshaw NS (editor) (2000). Special Is-sue on Dietary Approaches to Vitamin A Defi-ciency. Food Nutr Bull 21: 115-247

Seshadri S (editor) (1996). Use of Caro-tene-rich Foods to Combat Vitamin A Defi-ciency in India -a Multicentric Study. Sci Repno 12, Nutrition Foundation of India, New Delhi

Sherman MI (ed) (1986). Retinoids andCell Differentiation. CRC Press, Boca Raton,FLContains a chapter by SS Shapiro devotedto epithelial cell differentiation.

Shils ME, Olson JA, Shike M, Ross AC(eds) (1999). Modern Nutrition in Health andDisease, 9th edition. Lea & Febiger, Philadelphia.

Contains a chapter by JA Olson on“Carotenoids” and another by AC Ross on“Vitamin A and Retinoids” .

Simpson KL, Chichester CO (1981). Me-tabolism and nutritional significance ofcarotenoids. Ann Rev Nutr 1:351-374

Detailed source for Chapters 1 and 2.

Slater TF, Block G (eds) (1991). Antioxi-dant vitamins and β-carotene in disease pre-vention. Amer J Clin Nutr 53:189S-396S

Deals with the subject in the context of otherantioxidant nutrients in addition tocarotenoids.

Smitasiri S, Attig GA, Valyasevi A et al(1993). Social Marketing Vitamin A-RichFoods in Thailand. 2nd edition, Muhidol Uni-versity, Thailand

Sommer A (1982). Nutritional Blindness -Xerophthalmia and Keratomalacia. OxfordUniversity Press, New York

The most detailed account of xerophthal-mia, the subject of Chapter 5.

Sommer A (1995). Vitamin A Deficiency andits Consequences, 3rd edition. WHO, Geneva

A field guide to detection and control.

Sommer A, West KP Jr (1996). Vitamin ADeficiency: Health, Survival, and Vision. Ox-ford University Press, New York

The most comprehensive and up-to-dateaccount of virtually every aspect of VADD. Asacknowledged in the Preface, this SIGHTAND LIFE Manual has relied heavily on thisbook, but for full details original sourcesshould be consulted.

Sporn MB, Roberts AB, Goodman DS(eds) (1984). The Retinoids, vols 1 and 2.Academic Press, Orlando, FL


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Still an authoritative source, especially forthe more basic aspects.

Underwood BA (1986). The Safe Use ofVitamin A by Women During the Reproduc-tive Years. IVACG, ILSI-Nutrition Foundation,Washington, DC

Underwood BA (1994). Maternal vitaminA status and its importance in infancy andearly childhood. Amer J Clin Nutr 59: 517S-524S

Two documents that provide a good back-ground to more recent discussions.

van het Hof K (1999). Dietary Factors thatAffect Carotenoid Bioavailability. thesisWageningen University, Netherlands

Wasantwisut E, Attig GA (editors) (1995).Empowering Vitamin A Foods: A Food-basedProcess for the Asia and Pacific Region,Mahidol University, Thailand

WHO (1995). Global Prevalance of VitaminA Deficiency. WHO/NUT/95. 3, WHO, Geneva

The first detailed documentation of theworldwide extent of the problem of VAD (seeChapter 8).

WHO (1996). Indicators for Assessing Vi-tamin A Deficiency and their Application inMonitoring and Evaluating Intervention Pro-grammes. WHO, Geneva

Detailed proposals for assessment of VADat the subclinical level - relates especially toChapter 4.

WHO (1998). Safe Vitamin A Dosage Dur-ing Pregnancy and Lactation. WHO/NUT/98.4, WHO, Geneva

WHO Expert Group (1976). Vitamin A De-ficiency and Xerophthalmia. Tech Rep Ser no590, WHO, Geneva

The first international approach to definingthe nature and magnitude of the problem ofVADD.

WHO Expert Group (1982). Control of Vi-tamin A Deficiency and Xerophthalmia. TechRep Ser no 672, WHO, Geneva

The change of title signified that sufficientprogress had been made for greater atten-tion to be given to combating the problem.

WHO/UNICEF/IVACG (1997). Vitamin ASupplements. WHO, Geneva


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Glossary

Acute-phase reaction (or response)(APR) A generalized reaction of the body toacute infection. Certain proteins, positiveacute-phase proteins, increase in concentra-tion in plasma. Other proteins, which includeretinol-binding protein (RBP) and transferrin,decrease in concentration in plasma and areknown as negative acute-phase proteins.

Bioavailability In general the term refersto the degree to which any substance in thediet is available after ingestion for utilizationby the body. In the present context,bioavailability relates to the degree to whichdietary provitamin A carotenoids are utilizedafter ingestion.

Bitot’s spot Heaping up of keratinized cellson bulbar conjunctiva. An advanced stage ofconjunctival xerosis. The first description wasattributed to a French physician of that name inthe middle of the 19th century. Not all Bitot’sspots are attributable to deficiency of vitamin A.

Carotenoids Yellow, orange, or red pig-ments occurring in nature. About 600 havebeen identified, of which less than 10 haveprovitamin A activity. They all have a basicC40 skeleton which is made up from succes-sive additions of C5 isoprene units.

Chlorophyll A green pigment that impartsits colour to the leaves of plants and manyvegetables. It is mainly responsible for theprocess of photosynthesis, whereby in the

presence of sunlight carbon dioxide from theatmosphere and water are converted to car-bohydrate, and oxygen is given off.

Chloroplast This structure in leaves con-tains the chlorophyll and carotenoids, whichact as catalysts in the process of photosyn-thesis.

Cis/trans In olefin chemistry cis/trans is re-placed by E/Z for the unequivocal descrip-tion of a double-bond stereoisomer. For prac-tical reasons this was not implemented in thisManual; see isomerization.

Conjunctival impression cytology (CIC)A technique whereby a cellulose acetate stripis applied gently to the surface of the bulbarconjunctiva of the eye. When the strip is re-moved the superficial layer of epithelial cellsadheres to it. The strip with cells is processedand stained. The histological appearances arestudied for evidence of early keratinization,suggestive of subclinical VAD.

Dark adaptation The ability of the rod cellsof the retina of the eye to take over the func-tion of vision under conditions of low illumi-nation. This function is heavily dependent onan adequate vitamin A status.

Hypervitaminosis A Excessive vitamin Astatus in which there are excessive concen-tration of retinol in plasma and symptoms andsigns of toxicity.


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Hypovitaminosis A This is synonymouswith VAD.

Isomerization A change in the spatial ori-entation of a chemical molecule without anychange in the basic chemical structure.

Keratinization A process characteristic ofepithelial tissues. The tissues undergo a com-plex series of hardening and drying changes.Keratinization is normal in such tissues asskin, but is abnormal in many other epithelialtissues, including conjunctiva, cornea, andepithelial linings of lungs, gut, urinary tract etc.It is synonymous with the term xerosis.

Keratomalacia This term is applied tochanges in the cornea in severe VAD. In ad-dition to keratinization (see above) of the cor-neal epithelium there is softening of thestroma or underlying tissue.

Meta-analysis A statistical analysis appliedto the data of a group of studies which allconform to a set of criteria to ensure similar-ity as far as possible. The larger numbersobtained in this way provide greater statisti-cal power.

Night blindness The subjective sensationof difficulty to identify objects under conditionsof low illumination.

Provitamin A Carotenoids, like β-carotene,capable of being converted to vitamin A in theanimal body.

Recommended Dietary Allowance or In-take (RDA, RDI) This relates to the level ofan essential nutrient considered to be ad-equate to meet the known nutritional needsof practically all healthy persons in a popula-tion.

Relative dose response (RDR) A bio-chemical test designed to assess vitamin Astatus by the indirect estimate of liver vitaminA stores.

Retinoids A class of compounds consist-ing of four isoprenoid units joined together ina head-to-tail manner and customarily con-taining five conjugated double bonds. Theterm vitamin A is used as a generic descriptorfor retinoids exhibiting qualitatively the bio-logical activity of retinol.

Retinol equivalent (RE) This term was cre-ated to express both preformed vitamin A andprovitamin A carotenoid equivalents as a sin-gle nutritive value. One mg RE is equal to 1mg of all-trans retinol, or to 6 mg of all-transβ-carotene, or to 12 mg of other provitamin Acarotenoids.

Xerophthalmia A term that applies to allclinical stages of eye disease attributable toVAD.

Xerosis See keratinization.


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157

A

α-Carotene 2-3, 11, 13-4, 27Aceh (Indonesia) 64-9Acitretin 118-9Acne 118Actinic keratosis 118Acute promyelocytic leukaemia (APL) 119Acute lower respiratory tractinfections (ALRI) 72-4, 77, 106-7Acute-phase reaction (APR) 40, 72, 106Africa 12, 93, 95, 107Age 26, 101-2, 113Age-related macular degeneration (AMD)120All-trans retinol etc, see retinol etcAmericas 90, 95Anaemia 83-5Analysis, “intention-to-treat” 65

meta-analysis 64, 67, 73statistical methods 101

Animal products 9, 19Anthropometric status 80,Antioxidant 7, 35Apolipoprotein D 25Apricot 11Ascaris infestation 116Asia 91, 95, 104Astaxanthin 2

B

β-apo-8'-carotenal 14β-carotene 2-5, 11-18, 29, 133-4

in chronic diseases 119-209-cis β-carotene 4Bacteriuria 77Banana 14Bangladesh 54, 110, 125, 131, 135Beriberi 52Berries 14Bile salts 21Bitot’s spot (X1B) 38-9, 44, 46, 51-3, 56,58-9, 80, 110-1

and age 111prevalence of 111unresponsive 58

Black currant 14Body composition 80

reserves 40weight 79

Bogor (Indonesia) 65-7Breast-feeding 102-4, 125, 127

milk 43, 104retinol in 43, 48

Bronchitis 72-3Bronchopulmonary dysplasia (BPD) 116Bulging of the anterior fontanelle 126-7Buriti palm 11-2Butter 19

C

Canada 54Cancer 120Cape Town (RSA) 70, 74Carotenoids (see also individualcarotenoids)

Index


158

accumulation of 3actions 35analysis of 8bioavailability of 15-8functions of 35in cancer 119-21in chronic diseases 119-21in plasma 27-8mixed 11occurrence of 2provitamin A sources 10

Carrot 16Carr-Price reaction 8Carrot 11, 13Cassava 14Cataract 120Cell differentiation 31-2Cellular retinal-binding protein (CRALBP) 29Cellular retinoic acid-binding protein(CRABP) 29, 33Cellular retinoid-binding protein 28Cerebrovascular disease 121Chad 137Cheese 16“Chicken eyes” 46, 54(see also night blindness)Chicken pox 106Child spacing 105China 139Chlorophyll 6, 10, 15Chloroplast 6, 10, 15Cholecystokinin 21Chylomicron 23-4, 27

remnant 27Cicendo Eye Hospital (Indonesia) 73Cirrhosis of liver 116Clustering 110-1Cochlea 86Cod 19Coeliac disease 116Collagen type III 24Collagenases 60Colliquative necrosis 60 (see alsokeratomalacia)Community trials 64-7Complement C8γ 25Cone cells 31

threshold 55-rod transition time 55

Congenital malformations 33-4, 86, 118Conjunctiva 32, 39, 44, 51, 57-9

appearances 56Conjunctival Impression Cytology (CIC) 36-9, 44-6, 77, 85

with transfer (ICT) 44xerosis (X1A) 38-9, 44, 51, 57-8

Conjunctivitis 46Cornea 32, 39, 44, 51, 59-62Corneal scar (XS) 38, 51-2, 60-2, 97

ulceration 60, 107ulceration/keratomalacia (X3A, X3B)38, 51, 60xerophthalmia 51-62, 80, 105, 108xerosis (X2) 39, 51-2, 59

Coronary heart diseaseCorpus luteum 3Cryptoxanthin 2-3, 14, 27Cucurbita 11Cyclic AMP 35Cystic fibrosis 116Cytochrome P450 enzymes 30

D

Dairy produce 19Dark adaptation 39, 44, 46-9, 53-6Dark green leafy vegetables (DGLV) 10-2,15-6, 104-8Dermatological disorders 86Dermomalacia 60Deuterium isotope 16, 43Diarrhoeal diseases 66-8, 72-3, 75, 106,1083,4-Didehydroretinol 42Diet 103-4Dietary counselling 124,

intake assessment 47interventions 131-3

15,15'-Dioxygenase 22Disaster relief 124, 134Dopaminergic system 35Drumstick 135Durban (RSA) 75


159

E

Eastern Mediterranean Region 93, 96Economic/food policies 131Egg 13, 19, 132Elaeis guineensis 15

oleifera 15Electroretinography (ERG) 54Embryogenesis 33Emphysema 117Endoplasmic reticulum 23, 28Endosome 28Enzyme defectEpididymal-binding protein (EBP) 27Epithelial cell 32, 44

lining 81Erythropoietic purpura 120Etretinate 118-9European Region 92, 96Expanded Programme on Immunization(EPI) 128

F

Famine 134Far East 12Fat 17, 134Fibre 18Field trials 64-9Final rod threshold 39, 55-6Fish 13

fatty 19liver 19liver oils 19scales 46

Five-carbon units 5Food fortification 5, 19, 124, 129-31

law 129shortage 134

Fruit 10, 12, 132Fucoxanthin 2

G

Gac fruit 138γ-Carotene 2-3, 5Gap junction communication 35Gastrectomy 116Gastro-enteritis 108 (see also Diarrhoealdiseases)Gene expression 28-30

defects and VAD 116modification in rice 133-4

Genito-urinary tract 77Geranylgeranyldiphosphate 5-6, 134Ghana 66-9Giardia 116Glycoprotein 33Glycosaminoglycan 33Goblet cell 44-5, 57Golgi complex 24Grape 14Green vegetables 12, 132 (see also darkgreen leafy vegetables)Growth 34-5, 65, 79-81

adolescent 102linear 80-1stunting of 66, 79zinc and 85

Guatemala 84Gut 21-2, 73

H

Haemoglobin 84Haemopoiesis 34, 83-5Halibut 19Height/age 65Hemeralopia 46 (see night blindness)Hepatocyte 23Herpes simplex 107High-pressure liquid chromatography(HPLC) 7, 10HIV-AIDS 76, 108

in mothers 76Homeobox genes 34Human growth hormone 35Hyderabad (India) 66-9


160

Hypercarotenosis 120Hyperkeratosis 86Hypervitaminosis A (see also vitamin Atoxicity) 117Hypopyon 60

I

Immunity 34, 81-3cellular 81defensive response 82humoral 81natural killer (NK) cell 81offensive response 82retinoids and 83T-cell 34, 81-2

India 66-9, 87, 103, 105, 125Indonesia 63-9, 73, 87, 98, 109,Infectious disease 26, 53, 66-77, 82, 105-8

prevention and management 128severe 116systemic 105

Intervention, horticultural 131types of 123

Iodine deficiency disorders (IDD) 53Iodopsin 31β-ionone 3Iron 53

deficiency 34, 83-5status 83-5storage 34supplementation 83

Isomerization 4, 6Isopentenyldiphosphate 5-6Isoprene 5Isotope dilution 43Isotretinoin 118-9

J

Jaundice 116Jumla (Nepal) 66-9

K

Keratinization 57, 86Keratomalacia (X3A, X3B) 38-9, 51-2, 60-1,102, 113 (see also corneal xerophthalmia)Khartoum (Sudan) 66-9Kwashiorkor 105, 108

L

Lacrimal gland 52Lactation 36, 54, 102, 125-7β-Lactoglobulin 25Latin America 87, 90, 95Leaf concentrate 136Lecithin:retinol acyltransferase (LRAT) 23,29Lipocalin 25Lipoprotein, low-density 27-8

very low-density 27Liver 23-5

reserve 42-3sheep and ox 19structure 23

Lutein 2-3, 11-4, 27, 120Lycopene 2, 5-6, 11, 14-5, 27, 120Lymph 22-3

M

Macula 120Maize 104Malaria 76, 107Malawi 67, 110-1Mali 137Mango 11, 14, 108Marasmic-kwashiorkor 108Marasmus 108Margarine 19Maternal mortality 71Maternal stores 65Measles 68-70, 74-6, 107-8

and associated conditions 107-8case fatality rates 70complications 74-5


161

immunization in 128mortality 69-70outcome 75

Meat 19Meningococcal disease 77Micelle 21Micronesia 139Micronutrient Deficiency Information Sys-tem (MDIS) 87Milk 19, 43, 104, 134

skim 134Modified Relative Dose Response (MRDR)42, 48Monosodium glutamate (MSG) 129-30Morbidity 71-7,Mortality 63-71

and xerophthalmia 64cumulative 65prevention trials 65-9

Mucin 44-5, 57Muscle circumference 79

N

Neoxanthin 3Nepal 66-9, 102-3, 140Night blindness (XN) 38, 46, 48, 52-6, 110NNIPS (Nepal) 66-9Noncompliance 65Nutrition education 131Nutritional status 37Nyctalopia (see night blindness)

O

Opsin 30-2Optic nerve 86Orange 14Otitis media 77

P

Pacific region 94-6Palm oil extracts 15

species 15Pancreatic lipase 21Pancreatitis, chronic 116Papaya 11, 14, 108Parasitic infestation 18, 26, 106Pellagra 52Phospholipid 23Photosynthesis 10Physiological status 102-3Phytol 5Plant breeding 124, 133-4Pneumonia 68, 72-4Potato 14Poverty 103-4Pregnancy 19, 36, 55, 102-3, 118, 126-7Protein deficiency 108

status 18, 108Protein-energy malnutrition (PEM) 26, 53,63, 72, 107-9Psoriasis 118Public health 38, 40, 48, 125Pumpkin 11Pupillary contraction 39, 47

R

Rajasthan (India) 108-9Recommended Dietary Intake (RDI) 36,133-4Red palm oil 11-2, 14, 133Relative Dose Response (RDR) 24, 42, 48,106Reproduction 34, 86Respiratory disease 72, 66-8, 106-7, 109Retina, bleaching 32, 4611-cis retinal 1, 30-2Retinal-binding protein, cellular (CRALBP)29Retinitis pigmentosa 118Retinoic acid 1, 19, 23, 28-35

-binding protein, cellular (CRABP) 29, 33nuclear receptor (RAR) 28-9, 31(RXR) 24, 29, 31

9-cis retinoic acid 4, 29, 31Retinoids 4-6, 86

in general medicine 115-21


162

Retinol 1, 11, 19 (see also vitamin A )and iron 83-5in breast milk 43, 48in serum 16, 26, 38, 40-2, 48, 84, 87,106, 108

Retinol-binding protein (RBP) 8, 23, 25-8,40-1, 108membrane receptor 28

Retinol-binding protein/transthyretin molarratio (RBP/TTR molar ratio) 41Retinol Equivalents (RE) 11, 15, 36, 133-4Retinoyl beta-glucuronide RAG) test 41Retinyl ester 1, 11, 21-3, 27,

acetate, synthesis of 4Rhodopsin 1, 30-2, 57Rice 104Rickets 52Rod cells 30-2, 39, 46

scotometry 54Roots 12, 14Rotavirus infection 106

S

Sanitation 101Scurvy 52Sex differences 26, 111-4

in Bitot’s spot 111Shark, liver 19Sjogren’s syndrome 53Skin 60, 86Skinfold thickness 79SLAMENGHI mnemonic 16-8Small intestine 23South Africa 70South America 12South East Asian Region 91, 95,Spermatogenesis 34, 86Sprue 116Staple foods 104Starfruit 14Stellate cell 24-5Steroid-Thyroid-Retinoid Superfamily 29Subclinical-clinical divide 39Sudan 66-9,

Sugar, fortification of 83, 129-30Summer diarrhoea 108 (see diarrhoealdisease)Superficial punctate keratopathy (SPK) 59(see also corneal xerophthalmia)Sweet potato 11, 14

T

Tamil Nadu (India) 66-9Tanzania 70, 107Taro 14Teratogenic effects 33-4, 118, 126-7Terpene 5Tomato 10-1Trachoma 44Traditional eye medicine 107Transferrin 84Transthyretin (TTR) 25, 41Tretinoin 118-9Triglyceride 23Tuber 12, 14

U

United Kingdom 70Urinary tract 77

V

VAST (Ghana) 66-9Vegetable oil 12Vegetables 11, 35 (see also DGLV)Vegetarian 9Very low birth weight (VLBW) 116Vietnam 99, 138Violaxanthin 3Vision 30-2

restoration 46restoration time (VRT) 46

Visual cycle 32functions 30-2impairment 62


163

Vitamin Aabsorption 21-2bone modelling and 86capsule distribution 123, 125cellular uptake 28functions of 30-1in breast milk 43in nature 2in plants 5interventions 64-9, 123-4-iron interrelationships 83-5metabolism in liver 23-5methods of analysis 8occurrence 3preformed 19prophylaxis 126-8requirement of 36reserves 40-rich foods 131safety 126-7status, assessment of 37-50, 97storage form 1supplementation 126-8tissue 4toxicity 4, 33transport 23, 25-6treatment 123, 125-6units 10urinary excretion of 106

Vitamin A1 19Vitamin A2 19, 42Vitamin A deficiency (VAD)

control 123-40elimination of 123global occurrence of 87-99in experimental animals 72prophylaxis 123, 126-8public health importance 95season 108-10secondary (exogenous) 115-6subclinical 15, 39

Vitamin E 18Vitamin D 53Vitamin K 53Vomiting 126

W

Wasting 79Weaning diet 105Western Pacific Region 94, 96WHO, Geneva 87

X

Xanthophyll 3, 13Xerophthalmia (see also conjunctiva andcornea) 15, 51-64, 69, 73, 98-9, 103, 107,111-3

classification 38, 51criteria for 38, 52

Xerophthalmic fundus (XF) 38, 62Xerosis 32, 38-9, 44, 51-2, 57-60,

Z

Zambia 103, 110-1Zeaxanthin 2-3, 13, 27, 120Zinc 18, 120

interrelation with vitamin A 85-6

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