Background British South Asians experience excess cardiovascular disease (CVD) morbidity and mortality. Evidence for this is often based on studies using place of birth as a proxy for ethnicity. We examined the contribution of CVD risk factors and socio-economic position (SEP) to mortality in Europeans and South Asians, who provided confirmation of their ethnicity.
Methods South Asian and European origin individuals, aged 25–74 years, were recruited (April 1993 to March 1997). Ethnicity was determined by self-identified ancestry; at least 3 grandparents born in India, Pakistan or Bangladesh indicated South Asian ethnicity. Lifestyle, SEP, biochemical and anthropometric data were collected. Participants were mortality flagged with the NHS Medical Research Information Service. A lifestyle risk score, including BMI and self-reported physical activity, diet, smoking and alcohol consumption (range 0–5) was dichotomised to categorise a ‘healthy’ (score 0–2) or ‘unhealthy’ lifestyle (score 3–5). SEP was determined by the occupation of the head of the household. Age-adjusted hazard ratios (HR) for death were derived from Cox regression analyses.
Results 817 Europeans and 684 South Asians were followed up for 12-17 years. Mean follow-up was 14.9 and 13.9 years for Europeans and South Asians respectively. 5 Europeans and 34 South Asians were lost to follow-up, most commonly because individuals were no longer NHS registered (2 Europeans, 27 South Asians). Mortality ratios, standardised to a Newcastle-upon-Tyne European population, for Europeans and South Asians were 76.5 and 60.3 respectively (z-test of significance for difference between ethnic groups, p = 0.168). 28% and 49% of European men and women respectively (chi-square for difference, p < 0.001), and 23% and 26% (South Asian men and women, NS) were classified as having a healthy lifestyle. Having an unhealthy lifestyle was significantly associated with mortality in European women only (HR 1.8; 95% CI 1.03, 3.25). SEP was associated with mortality in European women and South Asian men (HR for manual vs non-manual occupation 3.1 [1.3, 7.5] and 3.7 [1.4, 9.9] respectively). SEP attenuated the effects of lifestyle on mortality in further models.
Conclusion No significant difference in SMR between Europeans and South Asians found at 12–17 years of follow-up, although in contrast to previous studies we report a higher SMR in Europeans than in South Asians. There was a trend towards higher mortality in those with a less healthy lifestyle, but this was statistically significant only in European women. Adjusting for SEP attenuated the relationship between lifestyle and mortality suggesting that both SEP and lifestyle influence mortality.
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