ORIGINAL ARTICLES

Mortality and Morbidity from Diabetesin South Asians and Europeans: 11-YearFollow-up of the Southall DiabetesSurvey, London, UKH.M. Mather*,1, N. Chaturvedi2, J.H. Fuller2

1Ealing Hospital NHS Trust, Uxbridge Road, Southall, MiddlesexUB1 3HW2EURODIAB, Department of Epidemiology and Public Health,University College London, 1-19 Torrington Place, London WC1E6BT

Over 20 % of middle aged and elderly South Asian people throughout the world havediabetes. The associated mortality and morbidity risks are unclear. We compared mortalityand morbidity in a cohort of South Asian and European people with diabetes in London,UK, in an 11-year follow-up of a population-based sample of 730 South Asians (mean age55 in 1984) and 304 Europeans (mean age 67 in 1984) with diabetes aged 30 years andabove in 1984. By 1995, 242 (33 %) of South Asians, and 172 (57 %) of Europeans haddied. The all-cause mortality rate ratio (South Asian versus European) was 1.50 (95 % CI0.72–3.12) for those aged 30–54 years at baseline. Ethnic differences in mortality rateswere abolished or reversed in people aged 65 years and above at baseline. The mortalityrate ratio for circulatory deaths was 1.80 (95 % CI 1.03–3.16, p , 0.05) and for heartdisease was 2.02 (95 % CI 1.04–3.92, p , 0.05) in those aged 30–64 years at baseline.Seventy-seven per cent of South Asian deaths were caused by circulatory disease, comparedwith 46 % of European deaths. South Asian survivors were 3.8 times (95 % CI 1.8–8.0,p = 0.001) more likely to report a history of myocardial infarction than Europeans. SouthAsian adults with diabetes show a markedly increased predisposition to cardiovasculardisease compared with Europeans, especially in younger people. This emphasizes theurgent need to reduce cardiovascular risk in this vulnerable group. 1998 John Wiley &Sons, Ltd.

Diabet. Med. 15: 53–59 (1998)

KEY WORDS Europeans; South Asians; mortality rates; circulatory disease; Ischaemic heartdisease

Received 1 May 1997; revised 21 August 1997; accepted 27 August 1997

usually assigned by country of birth. Ethnic differencesIntroductionin complications have been studied predominantly inhospital clinic populations, and, while some suggest thatPeople of South Asian descent living in the Indian

subcontinent, West Indies, South East Asia, Africa, and South Asians and Europeans are equally prone to diabeticcomplications,10,11 others indicate an increased risk ofthe UK have some of the highest diabetes prevalence

rates in the world.1–7 However, little is known about the nephropathy in South Asians.12–14

The Southall Diabetes Survey15 was one of themortality and morbidity risks associated with diabetes inSouth Asians, and these cannot be assumed to be similar first population-based studies to confirm the suspected

epidemic of diabetes in South Asian people in the UK.to those in Europeans. There are no reported prospectivepopulation-based studies comparing mortality and mor- Known diabetes prevalence was about four times higher

than in Europeans, a finding corroborated by subsequentbidity in South Asian and European diabetic people.Routine death certification data from the UK has suggested surveys on both known and total diabetes prevalence.7,16–18

We therefore attempted in 1995 to trace all those withthat cardiovascular mortality may be three times higherin South Asians compared to Europeans,8 but these data diabetes who had been ascertained 11 years earlier in

the Southall Diabetes Survey and examined the mortalitymay be misleading due to inaccuracies in the reportingof diabetes9 and the identification of ethnic group, and morbidity associated with diabetes in the two

ethnic groups.

Patients and Methods* Correspondence to: Dr Hugh Mather, Ealing Hospital NHS Trust,Uxbridge Road, Southall, Middlesex UB1 3HW, UK

The Southall Diabetes Survey15 was a door-to-doorSponsors: British Diabetic Association enquiry for known diabetes undertaken in 1984 in

53CCC 0742–3071/98/010053–07$17.50 1998 John Wiley & Sons, Ltd. DIABETIC MEDICINE, 1998; 15: 53–59

ORIGINAL ARTICLESSouthall, West London, UK. All residents were asked analyses (circulatory and ischaemic heart disease deaths)

to improve power, as the numbers of deaths in thesewhether anyone living at that address had been toldthat they had diabetes, and positive respondents were age groups were relatively small. Absolute mortality rates

for all causes of death by specific age groups in Southincluded in the study, whether they were on medicationor not. The area contained approximately 66 500 people, Asians and Europeans were calculated using the person–

years at risk approach. Cox’s proportional hazards modelsof whom about 34 000 were South Asian and 27 000European, and 1143 people with known diabetes were were then used to compare mortality risks from all

causes, circulatory disease (ICD 9 codes 390–459 orascertained. These people were retraced in 1995, usingseveral different data sources, including the databases of 798), and ischaemic heart disease (ICD codes 410–

414) adjusting for confounders which included age (asEaling Hammersmith and Hounslow Health Agency,Ealing Hospital, Ealing Diabetic Clinic, the Electoral discussed above), duration of diabetes and sex. The

assumptions of proportionality in the Cox’s models wereRegister and local general practitioners. The NationalHealth Service Central Register (Office of National tested by adding a term for the interaction of time with

the explanatory variable.19 This was found to be non-Statistics (ONS)) was used to confirm their currentwhereabouts and vital status. significant in the age-stratified analysis, indicating that

the proportionality assumptions had not been violated,Death certificates were obtained for those known tohave died on or before 15 October 1995, and were and that the models were valid. Odds ratios for compli-

cations were calculated using logistic regression. Dataclassified according to the 9th revision of the InternationalClassification of Diseases. Deaths were classified as being analysis were performed using the SAS20 and EGRET21

statistical packages.due to circulatory disease (which includes ischaemic heartdisease) when this was either specified as the underlyingcause of death by ONS, or when it appeared in the first Resultsor second line of the death certificate in those wherethe underlying cause of death was coded as diabetes. A total of 1143 people with known diabetes was

ascertained in 1984 (Figure 1). However, we found thatInformation on the cause of death was not available forthose who were known to have died while abroad but, 4 subjects had inadvertently been included twice, and

6 denied having diabetes when they received thewhere possible, we obtained the date of death from aclose relative. questionnaire in 1995. Of the remaining 1133, 1074

were either South Asian or European. The exclusion ofAll subjects who could be traced were sent a briefquestionnaire which enquired about a history of heart 22 South Asian and 18 European people aged below 30

years at baseline reduced the denominator to 1034attack requiring hospital admission, stroke, coronaryartery bypass graft operation or coronary angioplasty, diabetic people, of whom 730 were South Asian and

304 were European. The age distributions of these twoamputation of foot or leg, laser treatment for retinopathy,and renal transplant or dialysis. Non-responders were groups were markedly different, with mean ages in 1984

of 55 and 67 years, respectively (p = 0.0001). The meansent a further questionnaire, and persistent non-responders were visited by a field-worker. The question- known duration of diabetes in South Asians and Europeans

in 1984 was 7 and 8 years, respectively (p = 0.1).naire was piloted in 20 clinic attenders at Ealing hospitalwho had suffered at least one morbid event. There was When retraced in 1995, 242 (33 %) South Asians and

172 (57 %) Europeans had died. The absolute and relative100% concordance between self-reporting of morbidevents and the hospital case-notes. mortality rates from all causes of death varied significantly

by age group at baseline (p = 0.05 for interaction)(Table 1). The ratio of all-cause mortality in South AsiansStatistical Analysiscompared to Europeans was 1.50 (95 % CI 0.72–3.12)for those aged 30–54 years at baseline, but was 0.53The Southall Diabetes Survey included all age groups.

By 1995, there were only 3 deaths in those aged less (95 % CI 0.31–0.89) in those aged 75 years and aboveat baseline.than 30 years at baseline, and we have therefore excluded

these people from subsequent analyses. Mortality and Death certificate data were available for 198 (82 %)of South Asian deaths, and 166 (97 %) of Europeanmorbidity rates did not differ significantly between men

and women in either ethnic group, and both sexes have deaths. Circulatory disease accounted for 153 (77 %) ofthe South Asian deaths, including 114 (58 %) fromtherefore been combined for analysis.

The absolute and relative mortality rates in South ischaemic heart disease (IHD). In Europeans, 76 (46 %)had died from circulatory disease, including 43 (26 %)Asian and European diabetic subjects differed by age at

baseline (in 1984), and thus age-stratified analyses are from IHD. Mortality from circulatory disease and IHDwas 1.80 and 2.02 times higher, respectively, in Southpresented. These are further adjusted for age at baseline

(as a continuous variable within each age stratum), to Asians compared to Europeans in those aged 30–64years at baseline (p , 0.05) (Table 2(a),(b)). Mortality rateensure that imbalances in mean age within age groups

are accounted for. The younger age groups (30–54 and ratios (South Asian versus European) were also high inthe 65–74 years age group: 1.61 for circulatory death55–64) were grouped together for cause specific mortality

54 H.M. MATHER ET AL.

Diabet. Med. 15: 53–59 (1998) 1998 John Wiley & Sons, Ltd.

ORIGINAL ARTICLES

Figure 1. Flow diagram showing the vital status in 1995 of South Asian and European diabetic subjects ascertained in 1984 in theSouthall Diabetes Survey

Table 1. All cause mortality rates (per 1000 person-years) and rate ratios(South Asian versus European)

Age group South Asians Rate Europeans Rate Rate 95 % CI(years) deaths/n deaths/n ratioa

30–54 72/386 18.4 8/57 13.5 1.50 0.72–3.1255–64 95/220 49.4 22/63 39.3 1.20 0.75–1.9165–74 56/97 75.4 61/94 87.3 0.90 0.62–1.3175+ 19/27 116.3 81/90 200.3 0.53b 0.31–0.89

p = 0.05 for interaction between ethnicity and age group.aAdjusted for sex, duration of diabetes and age at baseline.bp , 0.05.

55MORTALITY AND MORBIDITY IN SOUTH ASIANS AND EUROPEANS WITH DIABETES

1998 John Wiley & Sons, Ltd. Diabet. Med. 15: 53–59 (1998)

ORIGINAL ARTICLESTable 2. (a) Mortality rate ratios (South Asian versus European) ratio 1.7, 95 % CI 1.1–2.8, p = 0.03). There were nofor circulatory disease (ICD 9 390-459 or 798.1) by age group significant ethnic differences in the prevalence of stroke,at baseline renal dialysis or transplant, hypertension, or amputation

of foot or leg.Age group South Asians Europeans Rate 95 % CI(years) deaths/n deaths/n ratioa

Discussion30–64 104/606 14/120 1.80b 1.03–3.1665–74 42/97 27/94 1.61 0.99–2.62 This is the first population-based comparison of mortality75+ 7/27 35/90 0.49 0.22–1.12 in South Asian and European people with diabetes. All

cause mortality rates were higher in South Asiansp = 0.01 for interaction with age.

compared to Europeans for the younger age groups,but this was not statistically significant. However, we

Table 2. (b) Mortality rate ratios (South Asian versus European) demonstrate that the risk of death from circulatory diseasefor ischaemic heart disease (ICD 9 410-414) by age groupand from IHD is twice as high in middle aged Southat baseline.Asians than in Europeans (aged 30–64 years at baseline),and about 1.5 times greater in the 65–75 years ageAge group South Asians Europeans Rate 95 % CI

(years) deaths/n deaths/n ratioa group. Cardiovascular disease is the most common causeof death in both groups, and accounts for an alarming

30–64 82/606 10/120 2.02b 1.04–3.92 77 % of all deaths in South Asians. These ethnic65–74 28/97 18/94 1.62 0.89–2.95 differences in mortality are similar to those found in the75+ 4/27 15/90 0.62 0.20–1.90

general population in the UK, although the twofoldincrease in cardiovascular mortality for South Asians inp = 0.2 for interaction with age.

aAdjusted for sex, duration of diabetes and age at baseline. the youngest age group is higher than the 1.5 timesbp , 0.05. increased risk that would be expected from general

population figures.22

The questionnaire data from survivors further emphas-and 1.62 for IHD. However in those aged 75 years andabove, mortality from circulatory disease or IHD in South izes the marked predisposition of South Asian diabetic

patients to IHD, with an adjusted odds ratio of 3.8Asians was about half that of Europeans.The ratio of all-cause mortality in women to men was compared to Europeans for a history of myocardial

infarction. The use of coronary revascularization pro-similar in South Asians (0.82, 95 % CI 0.62–1.07, p = 0.1)and Europeans (0.75, 95 % CI 0.54–1.03, p = 0.07). This cedures is also higher, with a combined odds ratio of

2.1. However, when the increased prevalence of IHDsex difference did not differ markedly across the agegroups. Only about a third of all death certificates in the South Asians is taken into account, the odds ratio

fell to 1.0, indicating that revascularization rates arementioned diabetes as a cause or contributory factor fordeath, but this proportion was similar in the two equal in the two ethnic groups. We have no data on

the presence of angina or the relative severity of IHD inethnic groups: 37 % in Europeans and 34 % in SouthAsians (p = 0.5). the two groups, but there are indications that South

Asians have more extensive disease post-infarction,23 butOf the 488 South Asians and 132 Europeans whowere not known to have died, 5 South Asians and 1 are less likely to be referred for an exercise stress test,24

and wait longer for angiography25 and specialist investi-European had emigrated, and 22 South Asians and 2Europeans could not be traced by the NHS Central gation.26

Despite the size of this cohort, relatively small numbersRegister, and their vital status was unknown. Completedquestionnaires were obtained from 414/461 (90 %) of of participants had experienced other severe diabetes

complications, such as amputation or end stage renalthe remaining traceable South Asians and 120/129 (93 %)Europeans. A history of myocardial infarction requiring disease. However, we do show that South Asians were

approximately one and a half times more likely to havehospital admission was 2.5 times as common in SouthAsians (20 %) as in Europeans (8 %) (Table 3). Adjustment had laser therapy for diabetic retinopathy. This does not

support findings from the UK Prospective Diabetesfor the younger age of South Asians further increasedthe odds ratio for a history of myocardial infarction to 3.8 Study,10 but the definition used for retinopathy there was

different, and patient selection into the study may(95 % CI 1.8–8.0, p = 0.001). Coronary revascularizationprocedures (angioplasty and bypass graft operations) also have biased the relationship between ethnicity

and retinopathy.were more commonly performed in South Asians thanEuropeans, with a combined odds ratio of 2.1 (95 % CI Studies of South Asian people worldwide show that

diabetes prevalence is approximately 20–30 % in middle0.8–5.7, p = 0.1). However, when adjusted for a historyof previous myocardial infarction, the odds ratio fell to aged people.27 The full impact of this strikingly high

prevalence has still not been realized because South1.0 (95 % CI 0.4–3.1, p = 1.0). A history of laser treatmentfor retinopathy was significantly more common in South Asian communities in many parts of the world, particularly

the UK, are relatively young compared to the generalAsians (36 %) than in Europeans (27 %) (adjusted odds

56 H.M. MATHER ET AL.

Diabet. Med. 15: 53–59 (1998) 1998 John Wiley & Sons, Ltd.

ORIGINAL ARTICLESTable 3. Prevalence of complications and adjusted odds ratios (South Asian versus European) from questionnaire data in 414 SouthAsians and 120 Europeans

South Asians Europeans Odds ratioa 95 % CI p value

n % n %

Myocardial infarction 82 20 9 8 3.8 1.8–8.0 0.001Coronary artery bypass graft 29 7 3 3 2.9 0.9–10.1 0.1Coronary angioplasty 15 2 2 4 2.3 0.5–11.5 0.3Stroke 53 13 11 9 1.9 0.9–3.9 0.1Renal dialysis/transplant 10 2 2 2 1.8 0.3–9.3 0.5Laser treatment for retinopathy 149 36 32 27 1.7 1.1–2.8 0.03Hypertension 189 45 47 40 1.3 0.8–2.0 0.2Amputation of foot or leg 12 3 3 3 1.0 0.3–3.9 0.9

aAjusted for age at baseline, diabetes duration, and sex.

population. For example, the application of the Southall bias in the severity of diabetes accounting for ethnicdifferences in mortality. We were not able to differentiateSurvey prevalence data to the 1991 census population

data has shown that the number of South Asian diabetic between Type 1 (insulin-dependent) and Type 2 (non-insulin-dependent) diabetes in this study. However, Typesubjects has increased by about 50 % in a decade,28

due to the changing population age-structure, with more 1 diabetes is relatively uncommon in South Asian people,and the proportion of diabetic people with Type 1 ismiddle aged and elderly South Asians. The total number

of South Asian diabetic subjects in UK in 1984 was thus likely to be higher in Europeans, particularly in theyounger age groups. As people with Type 1 diabetesestimated to be 25 000 from both the Southall Survey

and a British Diabetic Association questionnaire survey.29 have an especially high mortality rate, their inclusionwould serve to attenuate estimates of ethnic differencesThis has now probably risen to about 40 000. The

increased susceptibility of this large group to macrovacu- in mortality in people with Type 2 disease. Thus thetrue increased risk in cardiovascular mortality in Southlar disease is thus of enormous importance.

The apparent and unexpected improvement in survival Asian people may be greater than we report if only Type2 diabetes is considered. Information on cause of deathfound in elderly South Asian NIDDM subjects may relate

to several different factors. Firstly, and most importantly, was missing in a larger proportion of South Asians (18 %)compared to Europeans (3 %). This does not affectmany are unsure of their exact date of birth. The few

elderly South Asians ascertained in the survey may have comparisons of all cause mortality, but means thatthe relative risks in cardiovascular mortality are anexaggerated their age, causing the adjusted mortality

ratio to favour South Asians. Secondly, a greater number underestimate, as the proportion of all deaths due tocardiovascular disease is substantially higher in Southof South Asians (22, 4 %), than Europeans (2, 1 %),

could not be traced. A further 42 (6 %) South Asians Asians (76 %) compared to Europeans (46 %). It istherefore likely that many of the deaths ascertainedwere identified by the NHS Central Registry as being

alive, but we were unable to find them. It is possible where the cause was unknown were due to cardiovasculardisease, and as this proportion is greater in South Asiansthat some or many of these South Asians had died while

abroad, perhaps in the Indian sub-continent. However, than Europeans, we may have, if anything, underestimatedthe true burden of cardiovascular mortality in Southmost were relatively young, and if they had in fact died,

this would only increase the mortality differential in the Asians.The increased prevalence of previous myocardialyoung, and would not affect that in older age groups.

Finally, the lower mortality in elderly South Asians may infarction observed in South Asians compared to Euro-peans depended entirely on self report data. Patients hadreflect the selection of residual fit subjects, following the

higher mortality observed in younger age groups. This to be admitted to hospital, and had to recall that theadmission was due to an infarct. It would be easy tois consistent with findings from routine mortality data in

people with diabetes,8 and with the observation that the hypothesize that Europeans are more likely to beadmitted, and more likely to remember a diagnosis ofgreatest difference in prevalence of heart disease in non-

diabetic South Asians versus Europeans is found in myocardial infarction than South Asians, so that againwe may be underestimating the true burden of diseaserelatively younger age groups.30

Only diabetes known to the patient was ascertained in South Asians.The reasons for the increased risk of cardiovascularin the baseline study, but ethnic differences in the

prevalence of known diabetes corroborate closely with morbidity and mortality in South Asian compared withEuropean people are thought to relate to insulin resistance.subsequent surveys, some using population-based oral

glucose tolerance tests to ascertain diabetes.7,16–18 It is In the general population, South Asian people are moreinsulin resistant than their European counterparts, andtherefore unlikely that there is a systematic ethnic

57MORTALITY AND MORBIDITY IN SOUTH ASIANS AND EUROPEANS WITH DIABETES

1998 John Wiley & Sons, Ltd. Diabet. Med. 15: 53–59 (1998)

ORIGINAL ARTICLESlence and cardiovascular risk in South Asians. Lancetare therefore more likely to be glucose intolerant and1991; 337: 382–386.suffer from lipid disturbances.7 We were not able to

8. Chaturvedi N, Fuller JH. Ethnic differences in mortalitymeasure other cardiovascular risk factors in this cohort. from cardiovascular disease in the UK: do they persist inIn summary, these data show for the first time in a people with diabetes? J Epidemiol Community Health

1996; 50: 137–139.large population-based prospective study, that both9. Fuller JH, Elford J, Goldblatt P, Adelstien AM. Diabetesmortality and morbidity from ischaemic heart disease

mortality: new light on an underestimated public healthare markedly increased in middle aged South Asianproblem. Diabetologia 1983; 24: 336–341.

people with diabetes, with a two to three-fold excess 10. UK Prospective Diabetes Study Group. UK Prospectiveover their European counterparts. Circulatory disease Diabetes Study Paper XII: differences between Asian,accounts for three out of four South Asian deaths. These Afro-Caribbean and White Caucasian Type 2 diabetic

patients at diagnosis of diabetes. Diabetic Med 1994; 11:results emphasize the urgent need to reduce the alarming670–677.toll from macrovascular disease in this large high-risk

11. Nicholl CG, Levy JC, Mohan V, Rao PV, Mather HM.group. There are now evidence-based therapies which Asian diabetes in Britain: a clinical profile. Diabetic Medmay achieve this, such as aspirin, lipid lowering therapy, 1986; 3: 257–260.and ACE inhibitor agents.31 While these interventions 12. Allawi J, Rao PV, Gilbert R, et al. Microalbuminuria in

non-insulin-dependent diabetes: its prevalence in Indianhave mainly been tested in European populations, therecompared with Europid patients. Br Med J 1988; 296:is no a priori reason why they should not at least be462–464.equally effective in South Asians. The care of middle 13. Samanta A, Burden AC, Feehally J, Walls J. Diabetic

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14. Burden AC, McNally PG, Feehally J, Walls J. Increasedincidence of end stage renal failure secondary to diabetesmellitus in Asian ethnic groups in the United Kingdom.

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