VITAMIN- A

BY MOHAMED ABEDEGH

INTRODUCTION The word "vitamin" comes from the Latin word

vita, means "life".

Vitamins are chemicals found in very small amounts in foods.

“Vitamins have been defined as organic compounds which are required in tiny amounts to maintain normal health of organisms’.

cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet

CLASSIFICATION OF VITAMINS

FAT SOLUBLE A D E K

Water soluble B1- Thiamine B2- Riboflavin B3– Niacin B5 – Pantothenic acid B6 –Pyridoxine B8 – Biotin B 9 -Folic acid B12 -CyanoCobalamin C (Ascorbic acid)

Water soluble vitamins Fat soluble vitamins

Solubility Water soluble Fat soluble

Absorption Simple Along with lipids

Storage *No storage Stored in liver

Excretion Excreted Not excreted

Excess intake Nontoxic Toxic

Deficiency Manifests rapidly Manifests slowly

Treatment Regular dietary supply Single large dose

Difference b/w water soluble & fat soluble vitaminsVITAMINS

FUNCTION Vitamins have diverse biochemical functions. Some have hormone-like functions as regulators

of mineral metabolism (e.g. vitamin D) Regulators of cell and tissue growth and

differentiation (e.g. some forms of vitamin A) Others function as antioxidants e.g. vitamin E

and sometimes vitamin C The largest number of vitamins (e.g. B complex

vitamins) function as precursors for enzyme cofactors, that help enzymes in their work as catalysts in metabolism.

INTRODUCTION

Vitamin A is an essential nutrient needed in small amounts for the normal functioning of the visual system, and maintenance of cell function for growth, epithelial integrity, red blood cell production, immunity and reproduction.

Needed in lysosomal membrane stability Plays a role in keratinization,

cornification,

VITAMIN A CHEMISTRY Vitamin A occurs in two forms in food

Retinoids

Retinol

Retinal

Retinoic acid

Carotenes

α- carotene

β- carotene

γ- carotene

Retinol (vitamin A alcohol) :

N retinol plasma values: 15-30 mcg/dl in infants 30-90 mcg/dl in adults

RETINAL (VITAMIN A ALDEHYDE) :

This is an aldehyde form obtained by the oxidation of retinol.

Retinal and retinol are inter convertible.

RETINOIC ACID (VITAMIN A ACID) :

produced by the oxidation of retinal.

However, retinoic acid cannot give rise to the formation of retinal or retinol.

Beta-Carotene (provitamin A) : Found in plant foods. lt is cleaved in the intestine to produce

two moles of retinal

ABSORPTION OF VITAMIN A Retinoids

Retinyl esters broken down to free retinol in small intestine - requires bile, digestive enzymes, integration into micelles

Once absorbed, retinyl esters reformed in intestinal cells

90% of retinoids can be absorbed Carotenoids

absorption rate much lower Intestinal cells can convert carotenoids to

retinoids

TRANSPORT AND STORAGE OF VITAMIN A Liver stores 90% of vitamin A in the

body in form of Retinyl palmitate Reserve is adequate for several months Transported via chylomicrons from

intestinal cells to the liver Transported from the liver to target

tissue as retinol Free retinol is highly active but toxic &

therefore transported in blood stream in combination with retinol binding protein

EXCRETION OF VITAMIN A

Some lost in urine Kidney disease and aging increase risk

of toxicity because excretion is impaired

FUNCTIONS OF VITAMIN A Vision (night, day, colour) Epithelial cell integrity against

infections Immune response Haematopoiesis Skeletal growth Fertility (male and female) Embryogenesis

VITAMIN A AND BETA-CAROTENE Roles in the Body

Vitamin A in VisionHelps to maintain the corneaConversion of light energy into

nerve impulses at the retinaRhodopsin is a light-sensitive

pigment of the retina that contains a protein called opsin.

FUNCTIONS OF VITAMIN A: GROWTH AND DIFFERENTIATION OF CELLS • Retinoic acid is necessary for cellular

differentiation• Important for embryo development,

gene expression• Retinoic acid influences production,

structure, and function of epithelial cells that line the outside (skin) and external passages (mucus forming cells) within the body

VITAMIN A AND BETA-CAROTENE Roles in the Body

Vitamin A in Reproduction and GrowthSperm development in menNormal fetal development in

womenGrowth in childrenRemodeling of the bone involves

osteclasts, osteoblasts, and lysosomes.

FUNCTIONS OF VITAMIN A: IMMUNITY

Vitamin A deficiency also diminishes the ability to fight infections. In countries where children are not immunized, infectious disease like measles have higher fatality rates.

Even mild, subclinical deficiency can also be a problem, as it may Increase children's risk of developing respiratory and

diarrheal infections Decrease growth rate Slow bone development Decrease probability of survival from serious illness.

VITAMIN A AND BETA-CAROTENE Roles in the Body

Beta-Carotene as an AntioxidantBeta-carotene helps protect the

body from diseases, including cancer.(Lung, oral, and prostate cancers)

Prevention of cardiovascular disease

VITAMIN A DEFICIENCY

VITAMIN A DEFICIENCY

Causes Inadequate intake

Impaired absorption

Impaired storage and transport

Increased excretion [RBP]

Alcoholism

DAILY REQUIRMENTMen and women – 750-1000 μg.

Pregnancy and lactation – 1000 μg.

Infants – 350 μg.

Children – 400-600 μg.

DIETARY SOURCES OF VITAMIN A Vitamin A in Foods

Retinol is found in fortified milk, cheese, cream, butter, fortified margarine, and eggs.

Beta-carotene Spinach and other dark green leafy vegetables

(chlorophyll pigment masks the color) Deep orange fruits Deep orange vegetables like squash, carrots,

sweet potatoes White foods are typically low in beta-carotene.

Vitamin A is poor in fast foods and foods with the xanthophyll pigments (beets, corn).

Liver is rich in vitamin A.

VITAMIN A DEFICIENCY Vitamin A deficiency is a lack of vitamin A in

humans. Because vitamin A is stored in the body, it would take a year or more to develop a deficiency in the presence of inadequate intake.

Night blindness is one of the first signs of vitamin A deficiency.

Night blindness is the difficulty for the eyes to adjust to dim light. Affected individuals are unable to distinguish images in low levels of illumination. People with night blindness have poor vision in the darkness, but see normally when adequate light is present.

THE SIGNS OF VITAMIN A DEFICIENCY Ocular Night blindness. xerophthalmia bitot’s spot keratomalacia

Extra ocular Retarded growth Skin disorders Effect on

reproductive organs.

Effect on bone

XEROPHTHALMIA Conjunctiva become dry, thick and

wrinkled

BITOT’S SPOT Conjunctive keratinizes and develops

plaques- BITITS SPOT

Grayish white triangular spots in conjunctiva

KERATOMALACIA Infection leads to corneal ulceration and

total blidness

OTHER FEATURES OF VITAMIN A DEFICIENCY SKIN CHANGES- Scaly, toad like

(phrynoderma) Squamous metaplasia of respiratory

mucosa more prone to RESPIRATORY INFECTIONS

Alteration in mucosa of renal pelvis and UB formation of RENAL AND VESICAL CALCULI

Atrophy of germinal epithelium

© 2008 Thomson - Wadsworth

DIAGNOSIS OF VIT A DEFICIENCY Assessment of dietary vit.A Eye examination SERUM RETINOL level(normal level is

28 to 86 μg/dl (1 to 3 µmol/L) not an acurrate indicator unless the deficiency is severe and liver stores depleted

Night vision threshold test

TREATMENT

For VAD syndromes, treatment includes daily oral supplements, as follows: Children aged 3 years or younger - 600 mcg (2000 IU)

Children aged 4-8 years - 900 mcg (3000 IU) Children aged 9-13 years - 1700 mcg (5665 IU) Children aged 14-18 years - 2800 mcg (9335

IU) All adults - 3000 mcg (10,000 IU) Therapeutic doses for severe disease include

60,000 mcg (200,000 IU), which has been shown to reduce child mortality rates by 35-70%

PARENTERAL WATER SOLUBLE VIT. A DOSE- 3/4th DOSE <6 months ½ DOSE 6-12 months

INDICATION- 1. Impaired oral intake2. Persistent vomiting3. Severe malabsorption

RECOMMENDED XEROPHTHALMIA TREATMENT SCHEDULE

6 -12 months > 1 yr Immediately 100,000 IU 200,000 IU Next day 100,000 IU 200,000 lU 2–4 weeks later 100,000 IU 200,000 IU

Severe Protein-Energy Malnutrition (PEM) Monthly until PEM resolves 100,000 IU 200,000 IU

LOCAL TREATMENTCORNEAL ULCER-ANTIBIOTICS DROPS/OINT. THRICE DAILY(to prev. sec. infection)PADDING OF EYE (to prevent dehydration and

furthur corneal exposure)MYDRIATIC- ATROPINE DROP 1% OR OINT.

ONCE DAILY

PREVENTION mothers of breast-fed infants living in

regions where vitamin A deficiency is common.

2 doses of 200,000 IU (60 mg) of vitamin A are given to the mother immediately after delivery,

and the infant is given 3 doses of 25,000 IU (7.5 mg) of vitamin A at 1-3 mo of age

PREVENTION CONSUMPTION OF FOODS RICH IN

VIT A LONG TERM PREVENTION

STRATEGIES1. Nutrition education and dietary

diversification2. HORTICULTURAL INTERVENTION incl.

Home gardening3. Nutritional supplementation4. Selective fortification for high risk and

special groups

All Infants with birth weight of ≤1 kg should receive 5000IU of Vitamin A i.m 3 times a week for first 4 weeks- slightly reduce the incidence of chronic lung disease

Manual of neonatal care – john p cloharty, 6th ed

HYPERVITAMINOSIS A Hypervitaminosis A refers to the effects of

excessive vitamin A) specifically retinoid) intake Hypervitaminosis A occurs when the maximum

limit for liver stores of retinoids is exceeded. The excess vitamin A enters the circulation causing

systemic toxicity. Betacarotene (is an organic compound which is a

strongly-coloured red-orange pigment abundant in plants and fruits. β-Carotene is also the substance in carrots that colours them orange) a precursor of vitamin A, is selectively converted into retinoids, so it does not cause toxicity.

© 2008 Thomson - Wadsworth

HYPERVITAMINOSIS AAcute Intoxication: Infants: drowsiness or irritability

w/signs of increased ICP Adults: drowsiness, irritability,

headache & vomiting Serum vitamin A values = 200-1000

IU/dl (N: 50-100 IU/dl)

TOXICITY OF VITAMIN AAcute – symptoms disappear when intake stops GI effectsHeadachesBlurred visionPoor muscle coordination

CHRONIC INTOXICATION Results when >50,000 IU/day ingested for

several wks or more Signs & symptoms in infants:

Early are anorexia, pruritus, irritability, tender swollen bones w/motion limitation

Alopecia, seborrhea, cheilosis & peeling of palms & soles

Hepatomegaly & hypercalcemia observed Craniotabes & hyperostosis of long bones

Elevated serum vit A levels confirms diagnosis

Reversible manifestations when vitamin A discontinued

POLAR BEAR

One ounce of polar bear liver contains enough vitamin A (retinol) to kill a person!