Differences in biological risk factors for cardiovascular disease between three ethnic groups in the Whitehall II study
Introduction
Ethnic differences in cardiovascular mortality in Britain provide a paradox. South Asians and Afro–Caribbean’s both share a number of factors considered to be risk factors for cardiovascular disease, including hypertension, glucose intolerance and poverty. South Asians have high rates of ischaemic heart disease deaths compared to the white population. This applies to all the cultural and racial groups who can be broadly classified as South Asian, although they are culturally and ethnically distinct [1]. Afro–Caribbeans, however, have a lower incidence of ischaemic heart disease than the white population, but have higher rates of stroke and higher prevalence of hypertension [2].
One of the formidable problems with trying to investigate ethnic differences in health in Britain is that ethnic minorities currently tend to be congregated towards the lower end of the socio-economic structure. Cardiovascular disease is strongly influenced by socio-economic status in all societies, whether one considers accepted risk factors, heart disease, hypertension or stroke [3], [4].
Disentangling the effects of socioeconomic status and ethnic background is therefore difficult, and it is a major potential confounding factor in most studies that have been undertaken. Some, although not all, of the apparent differences between ethnic groups may be explained by socio-economic factors [5]. The Whitehall II study provides a good opportunity to compare socio-economically broadly similar groups from different ethnic backgrounds. It is restricted to an occupational cohort with only employed London-based civil servants as participants. In addition it has data on many socio-demographic indicators, in particular employment grade, as in part it was set up to answer questions about the effects of inequalities of health across different social strata [6]. This enables relatively precise methods of controlling for confounding by socio-economic factors to be employed.
Section snippets
Methods
The Whitehall II study is a cohort study of 10 308 civil servants. The target population was all London based office staff aged 35–56 between 1985 and 1988. There was a 73% response rate in phase 1, with the true response rate likely to be higher because around 4% of those in the list of employees had moved before the study started. All staff had an initial health screening questionnaire, along with psychological, dietary and social questionnaires. All participants are classified by employment
White Europeans
There are 8973 individuals classified as white; 6159 (69%) men, 2814 (31%) women. Mean age at first screening was 43.8 (range 34–56). Distribution across the grades in the civil service is shown in Table 1.
South Asians
There were 577 individuals classified as South Asian; 357 (62%) men, 220 (38%) women. Mean age at first screening was 46.3 (range 35–55). They are mainly clustered to the lower end of the grade structure (Table 1), with 50% in clerical or support grades. Car and home ownership is the same as
Discussion
This study examines differences in established risk factors for cardiovascular disease between three ethnic groups in an employed cohort. A major difficulty in looking at ethnic differences is controlling for the effects of socio-economic status, which is a potential confounding factor. Consistent with this, we have shown that metabolic risk factors are systematically related to employment grade among whites [8]. The strength of this study is that by restricting it to employed civil servants,
Conclusion
Data from the Whitehall II study support previous findings that South Asians have hypertension and insulin resistance associated with adverse lipid profiles. Afro–Carribeans have hypertension and insulin resistance but favourable lipid profiles and also have more favourable alcohol and smoking patterns. This study demonstrates that whilst socio-economic factors play some role in these relationships, in the two main ethnic minority populations in Britain they cannot be fully explained by
Acknowledgements
C.W. was supported by an MRC studentship. E.B. and M.S. are supported by the British Heart Foundation. M.M. is supported by an MRC research professorship. We thank all participating Civil Service departments and their welfare, personnel and establishment officers; the Civil Service Occupational Health Service; the Council of Civil Service Unions and all participating Civil Servants. Supported by grants from the Medical Research Council, Health and Safety Executive, British Heart Foundation,
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