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New answers to three questions on the epidemic of coronary mortality in south Asians: incidence or case fatality? Biology or environment? Will the next generation be affected?
  1. M Justin Zaman1,
  2. Raj S Bhopal2
  1. 1Department of Cardiology, James Paget University Hospital, Great Yarmouth, Norfolk, UK
  2. 2University of Edinburgh, Edinburgh, UK
  1. Correspondence to Dr M Justin Zaman, Department of Cardiology, James Paget University Hospital, Lowestoft Road, Gorleston-on-Sea, Great Yarmouth, Norfolk NR31 6LA, UK; justin.zaman{at}jpaget.nhs.uk

Abstract

Studying ethnic differences in health not only benefits minority groups but is a powerful tool for scientific analysis and for social action in the wider field of health inequalities. Coronary mortality in developed countries is well-known to be higher for men and women born in south Asia compared to other ethnic groups. The aim of this review is to examine how the knowledge of ethnic differences in coronary health in south Asians has advanced in the last decade. We set out to answer the following: Is the high rate of coronary mortality in south Asians a result of high incidence or high case fatality? Why are there ethnic differences, and are they the result of biology, healthcare or social circumstances? Is the cardiovascular health future for south Asians (and especially the UK-born second generation) any brighter than in their parents?

  • Cardiac prevention
  • cardiovascular disease
  • clinical coronary heart disease
  • community cardiology
  • coronary prevention
  • diabetes
  • epidemiology
  • ethnic variations
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The study of ethnic differences in health is not only of potential benefit to minority groups, but to the whole population—as studying ethnic inequality is a powerful tool for scientific analysis and for social action in the wider field of health inequalities.1 UK studies of mortality in the 1970s and 1980s highlighted differences in cause of death between different immigrant groups,2 ,3 and analyses around the 2001 UK census noted that rate ratios for coronary mortality were higher for men and women born in south Asia.4–6 The aim of this review is to examine, primarily but not wholly in the UK context, how knowledge of ethnic differences in coronary mortality in south Asians has advanced in the last decade. This review is not systematic but we have three questions that we have set out to answer based on our knowledge of the literature and fresh literature searches.

The questions are:

  1. Is the high rate of coronary mortality in south Asians a result of high incidence or high case fatality?

  2. Why are there ethnic differences, and are they the result of biology, healthcare or social circumstances?

  3. Is the cardiovascular health future for south Asians (and especially the UK-born second generation) any brighter than in their parents?

Is the high rate of coronary mortality in south Asians a result of high incidence or high case fatality?

The higher coronary mortality rate in south Asian compared to the white population may be either a consequence of a higher incidence of coronary disease in south Asian populations or a worse prognosis of already-manifested coronary disease—or a combination of both. Evidence to separate the contributions of disease incidence and prognosis requires, respectively, incident events in population cohort studies and the examination of outcomes in clinical cohorts with coronary disease. Much of the older work in this field consisted of cross-sectional analysis of mortality statistics or cross-sectional surveys rather than cohort studies, as found by the last systematic review in this field published in 2000,7 which retrieved 19 studies. Since this 2000 review, evidence from retrospective and follow-up of cross-sectional surveys (turning them into cohort studies) has been published.

The paper of Fischbacher et al8 in 2007 examined the incidence of fatal and non-fatal myocardial infarction through a record-linked, retrospective cohort study of 4.6 million people that linked individual ethnic groups from the 2001 census to Scottish hospital discharge and mortality data from 2001 to 2003. The incidence of acute myocardial infarction (fatal combined with non-fatal) was higher in south Asian compared to non-south Asian men, with a similar picture reported in women. In subsequent analyses this study has shown a higher incidence of stroke, chest pain, angina, myocardial infarction and heart failure, all using the combined endpoint of hospitalisation or community death.9–11 Forouhi et al12 found a higher incidence of coronary death in 1420 south Asian men recruited in west London compared to 1787 European men. Furthermore, south Asians also have a higher incidence of earlier phenotypes of coronary disease. Over 18-year follow-up of London healthy civil servants in the Whitehall II study, south Asians had higher cumulative frequencies of typical angina (17.0% vs 11.3%, p<0.001) compared with white individuals.13

Is the prognosis of already-manifest coronary disease also worse in south Asians? The study by Fischbacher et al8 further examined prognosis following myocardial infarction. After adjustment for age, sex and any previous admission for diabetes the hazard ratio for death at two years was 0.59 (95% CI 0.43 to 0.81), reflecting better survival among south Asians. This was a major surprise. In as yet unpublished data, with a longer follow-up to 2008, the same study has shown this finding especially in Pakistani-origin women in Scotland (personal communication, R.S. Bhopal, Scottish Health and Ethnicity Linkage Study). Using a similar study design with routinely collected hospital administrative data linked to cardiac procedure registries from British Columbia and the Calgary health region area in Alberta, Canada, Khan et al14 reported that south Asian patients had a lower relative risk of long-term mortality compared with white patients (hazard ratio 0.65; 95% CI 0.57 to 0.72), while in-hospital and longer-term mortality of south Asians appeared no worse than that of Caucasians in a study of 9771 patients who underwent percutaneous coronary intervention in a London teaching hospital serving a large south Asian community (18.5% were south Asian, with diabetes being far more prevalent in south Asians at 45.9±1.2% vs 15.7±0.4%, p<0.0001 in Caucasians).15 These new studies have contradicted some earlier reports, but it looks like the outcome after presentation with coronary disease is not worse in south Asians in spite of their high prevalence of diabetes.

The resulting conclusion is that to reduce persisting ethnic disparities in coronary mortality, policy needs to concentrate on reducing ethnic inequalities in disease incidence (ie, primary prevention). The combination of higher incidence and equitable or even better prognosis in south Asian compared to white populations of coronary disease, coupled with the general ageing of the whole UK population, will lead to an increase in the size of the prevalent pool of south Asian people with coronary disease. South Asian populations may also continue to experience increased morbidity following presentation with acute coronary disease on account of their higher rates of diabetes and this disease's ensuing complications. A cohort of patients with angina undergoing coronary angiography showed that although prognosis in terms of subsequent events such as myocardial infarction and death was not worse in south Asian compared to white populations, south Asian patients were less likely to experience long-term improvement in angina following coronary revascularisation when compared to white patients.16

Why are there ethnic differences, and are they the result of biology, healthcare or social/behavioural circumstances?

Biology

The reason behind ethnic differences in coronary disease was long thought to be metabolic, particularly insulin resistance—the prevalence of the metabolic syndrome being highest in south Asians.17 It has been long known that south Asians have substantially higher rates of diabetes.18 However, there have been no population-based large-scale cohort studies with sufficient power to examine prospectively the relationship between the south Asian metabolism and coronary outcomes.19 Contemporary studies such as the London Life Sciences Prospective Population (LOLIPOP) study in west London and the Biobank UK will provide data to explore this in large populations. Recent follow-ups of the Southall and Brent cross-sectional studies have, surprisingly, been unable to explain the relatively high rates of coronary disease in south Asians on the basis of insulin resistance and metabolic variables.12 Certainly, it seems clear that there is a predisposition in south Asians to develop metabolic abnormalities that lead to diabetes earlier and thus contribute to earlier and more incident coronary disease, but where in the life cycle this emerges is not clear, nor is it yet clear what could be done about it, although the results of diabetes prevention trials are quite promising.

The classic hypotheses of the thrifty genotype20 and the thrifty phenotype21 have been supplemented by four recent ideas: the soldier-to-diplomat,22 variable disease selection,23 mitochondrial efficiency,24 and adipose tissue compartment25 hypotheses. A full exposition of these and other hypotheses is beyond the scope of this paper but we wish to mention one—the adipose tissue compartment hypothesis proposes that south Asian populations have a smaller superficial subcutaneous adipose tissue compartment than white populations and that as babies born to mothers of south Asian descent are both smaller and have less capacity in this compartment. During subsequent growth and development while immersed in the richer diet of the developed world, this primary compartment reaches its capacity for fat storage rapidly and the deep subcutaneous and visceral compartments become more prominent, with adverse consequences for risks of diabetes and coronary disease.25 Subsequent work has shown that subcutaneous abdominal adipose tissue is more significantly associated with the metabolic syndrome when compared with intra-abdominal adipose tissue in Asian Indians.26 This exemplifies the renewed efforts in the past decade to understand this phenomenon, and we have definitely come closer.

Healthcare

Do south Asians get worse healthcare? The evidence suggesting better survival among south Asians suggests that—at least in studies of manifest coronary disease since the year 2000—there is little contemporary evidence of ethnic inequities in healthcare access and provision for cardiovascular health in the UK. Outcomes of out-of-hospital cardiac arrest in London are similar in south Asians as in other populations.27 In populations already selected for coronary angiography, south Asians have been shown not to be inequitably managed in terms of prescription medication.28 Access to coronary revascularisation services may paradoxically be better in more deprived areas (where most large UK south Asian communities are located) due to their proximity to specialist cardiac centres.29 The introduction of pay for performance incentives in UK primary care has led to more equitable management of coronary disease across ethnic groups.30 The 2001 Census and quality and outcomes framework data suggest that statins, which play an important role in improving prognosis,31 are more highly prescribed in south Asians—thus this high-risk group is being addressed appropriately in the NHS.32

Social/behavioural circumstances

The social heterogeneity of south Asian people becomes particularly important when comparing behavioural practices that may in turn determine a shift in future epidemiological disease patterns. South Asian people are part of a heterogeneous group composed of different nationalities and religions (eg, Indians, Pakistanis and Bangladeshis; Muslims, Sikhs and Hindus). Bhopal et al33 cemented their arguments for disaggregating south Asian groups in the context of cardiovascular health by demonstrating the huge differences in risk factor patterns in Bangladeshis (worst), Pakistanis (intermediate) and Indians (best) in Newcastle. These findings have been backed up by analyses of data from the Health Surveys for England, showing that, for example, Bangladeshi men have much higher smoking rates (36%) than white individuals or indeed other south Asian groups34—Indian men smoked much less than all including white populations (15%). Much of the UK Bangladeshi community is classified as having low socioeconomic status, high rates of unemployment and low levels of formal female employment,35 and this social deprivation is one explanation for their higher smoking levels in these health surveys. However, smoking is still uncommon in Bangladeshi women in these surveys, pointing to cultural factors.36 As much as healthcare has improved, it seems likely that ethnic disparities in disease will remain as long as there are social disparities, especially those that are associated with cardiovascular risk factors. Further evidence that ethnic differences in coronary health may be more to do with social rather than biological factors can be inferred from a study of coronary mortality by specific country of birth across Denmark, England and Wales, France, The Netherlands, Scotland and Sweden. This work is of much interest as previous work has focused mostly on the south Asian diasporas in the UK and Canada. It showed that for most country of birth groups—China, Pakistan, Poland, Turkey and Yugoslavia—there were substantial between-country differences.37 This emphasises that environmental, demographic and social factors influence disease occurrence in each national context, as these are not similarly distributed across countries.

The INTERHEART investigators have shown that the main risk factors for coronary disease in populations equally apply to south Asians.38 Their case–control study was of 1732 patients presenting with their first acute myocardial infarction alongside 2204 controls matched by age and sex from 15 medical centres in five south Asian countries, alongside 10 728 cases and 12 431 controls from other countries. The authors showed that the majority of risk in these native south Asians could be explained by nine potentially modifiable risk factors with similar collective impact as in other countries. The authors thus concluded that the earlier age of myocardial infarction in south Asians was a result of their higher risk factor levels at a younger age. What was interesting here was that the paper was studying south Asians who had not migrated to richer countries, but showed that conventional risk factors, if carefully measured, were associated with coronary disease in the same way as they were in the developed world. The paper thus suggested that concentrating on ethnicity alone was the wrong approach—considering that Bangladeshis in Bangladesh had the highest prevalence of most risk factors among the controls (smoking at 59.9% for example) and perhaps surprisingly the lowest prevalence for regular physical activity (1.3%) and daily intake of fruits and vegetables (8.6%). The paper infers that coronary disease is thus caused by lifestyle and behaviour wherever you live, irrespective of your ethnicity. The marked variation in the age of presentation of myocardial infarction in south Asians, with Bangladeshis being the youngest and Nepalese the oldest, indicated further that the onset of incident coronary disease can be delayed by modifying risk factors.

Is the cardiovascular health future for south Asians (and especially the UK-born second generation) any brighter than in their parents?

Despite the now well-known higher coronary risk profile in south Asians and the efforts of primary care, public health, the NHS and charities among others to educate the south Asian population, there is mostly bad news concerning positive changes in south Asian lifestyles. Although no new widespread study of behavioural patterns pertaining to future coronary disease in south Asians has been undertaken since the 2004 Health Survey for England,39 there are few encouraging reports of any improvements in the personal risk factor profile. For example, levels of physical activity have long been known to be lower in south Asian people than the general UK population, as reported in a systematic review of studies describing levels of physical activity and fitness in 2004.40 These findings remain consistent with more contemporary work.41 The case to promote physical activity in south Asian communities for the primary and secondary prevention of coronary disease and diabetes has been made for almost a decade,42 and there is little evidence of successful interventions among south Asian groups to rectify this.43 This is of huge concern considering research that shows that physical inactivity may explain more than 20% of the excess coronary mortality in the south Asian population, even after adjustment for potential confounding variables (such as socioeconomic position, smoking, diabetes and existing cardiovascular disease).44 Efforts have included ‘Khush Dil’, a community-based cardiovascular risk control project for south Asians in Edinburgh,45 which led to an improvement in risk factor profiles at 6–12 months follow-up, for example, reduction in cholesterol (0.19 mmol/l; 95% CI 0.1–0.37), in diastolic and systolic blood pressures (3.15 and 3.7 mm Hg, respectively) and in weight (0.61 kg; 95% CI 0.22–1.02). The follow-up period in these projects cannot, of course, examine whether the impact would be long lasting, or whether it would impact on disease outcomes and, of course, the sustainability of these projects—often funded by one-off grants—is far from guaranteed. Project Dil was a similar programme for reducing risk factors among south Asians in Leicester, which was then adopted by Leicestershire health services as a mainstream programme,46 which continues to this day as an education course available in Gujarati, Punjabi, Urdu and Bengali (DESMOND BME http://www.leicestershirediabetes.org.uk/430.html). The South Asian Community Health Education and Empowerment Campaign (SACHE) programme was designed by the UK charity South Asian Health Foundation to provide health education to patients, the public and health professionals, for the primary and secondary prevention of heart disease (personal communication, M.J. Zaman, South Asian Health Foundation cardiovascular group) but again, long-term outcomes and guarantees about sustainability are lacking.

Most of the data pertaining to ethnic inequalities in coronary disease concern migrants from south Asia. Many UK-born south Asian people are now entering their 40s and 50s, as migration from south Asia into the UK only began in significant numbers after about 1955. However, it is critically important to know whether the children of first-generation south Asian migrants will be at equal risk to their parents. Data on this are increasing, and generally the findings are worrying. For example, south Asians (mostly Pakistani/Bangladeshis) were found to be more likely than white majority groups to engage in poor dietary behaviours in a study of both adolescent and parental lifestyles, with those born in the UK and girls being more susceptible.47 UK south Asian children have higher adiposity levels (measured by skin-fold thickness) when compared with white Europeans,48 while ethnic differences in diabetes precursors are already present in apparently healthy children before the age of 10 years, with most of the ethnic differences in diabetes precursors following the pattern seen in adults.49 Therefore, the ethnic differences in type 2 diabetes susceptibility first described in immigrants to the UK seem to be persisting in UK-born south Asian children. A combination of high susceptibility relating to their origins with an affluent lifestyle with a high prevalence of cardiovascular risk factors from birth (whereas their parents were mainly exposed in early adulthood when most migrated) heralds a continuation of the cardiovascular disease epidemic in this population. So what do we need to do?

Towards action

It is clear that south Asians have a greater predisposition to cardiometabolic dysfunction for reasons that are under intense study (see above new hypotheses), but that the risk factors that finally result in coronary disease are well established ones. Therefore, the answer is to prevent, and this means preventing the adoption of lifestyles that raise risk. Modification of risk factors and behaviour should take place in school and continue through to adulthood. South Asian children need to eat healthier, avoid central obesity, undertake physical activity daily and not take up smoking. They should not wait for their 20 s and 30 s to develop healthy lifestyles. Their families and communities (cultural and healthcare) must support them. Social determinants of behaviour are important and thus healthcare policy should be public health led, not healthcare led. The priority for further research in this area should be about the development, evaluation and implementation of effective epidemiological interventions. Research should seek to monitor trends and highlight progress—if it is being made—in reducing risk factors, disease incidence and delaying the onset of coronary disease in south Asians.

Conclusions

We set out to answer three questions. First, the primary problem is higher incidence rather than higher case fatality. While improvements in both reduced incidence and better survival are desirable, it is the persisting higher incidence of coronary disease in south Asian populations that needs special focus, as survival from coronary disease appears at least equitable, if not better in south Asian compared with white populations. Second, the causes appear to be a combination of underlying biological factors—probably adipose tissue distribution and metabolism—and environmental, demographic, social and behavioural factors. Third, the cardiovascular health future for the UK-born second generation is gloomy unless the prevention of coronary disease in south Asians starts at least a decade earlier. With early action, incidence will be driven down, disease will present later and given continuing equality in healthcare, we can predict this particular ethnic difference in coronary disease will narrow.

References

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Footnotes

  • Competing interests MJZ is deputy chair and RSB is a patron of the South Asian Health Foundation, a UK-based charity.

  • Provenance and peer review Commissioned; internally peer reviewed.

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