Do cardiometabolic, behavioural and socio-economic factors explain the ‘healthy migrant effect' in the UK? Linked mortality follow-up of South Asians compared to White Europeans in the Newcastle Heart Project

Background
Immigrants are sometimes found to have better health than locally born populations. We examined the mortality experience of South Asian origin and White, European origin individuals living in Newcastle upon Tyne, UK.
Methods
A linked 17-21 year mortality follow-up of a cross-sectional study of European (n=825) and South Asian (n=709) men and women, aged 25-74 years, recruited between 1993-7. Poisson regression was used to estimate mortality rate ratios (MRR) for all-cause mortality. Sensitivity analysis explored the possible effect of differences between ethnic groups in loss to follow-up. The impact of adjustment for established risk factors on MRRs was studied.
Results
South Asians had lower all-cause age and sex adjusted mortality than Europeans (MRR 0.70; 95% confidence interval 0.58, 0.85). There was higher loss to follow-up in South Asians. Sensitivity analyses demonstrated that this did not account for the observed lower mortality. Adjustment for cardiometabolic, behavioural and socio-economic characteristics attenuated but did not eliminate the mortality differences between South Asians and Europeans, although confidence intervals now cross 1 (MRR 0.79; 95% confidence interval 0.55, 1.13).
Conclusions
South Asians had lower all-cause mortality compared to European origin individuals living in the UK Newcastle upon Tyne that were not accounted for by incomplete mortality data. It is possible that such migrants to the UK have the resources and motivation to move in search of better opportunities, and may be healthier and wealthier than those who remain in their country of origin. These findings challenge us to better understand and measure the factors contributing to their survival advantage.