Mitigating effect of immigration on the relation between income inequality and mortality: a prospective study of 2 million Canadians

Background The relation between income inequality and mortality in Canada is unclear, and modifying effects of characteristics such as immigration have not been examined. Methods Using a cohort of 2 million Canadians followed for mortality from 1991-2001, we calculated HRs and 95% CIs for income inequality of 140 urban areas (Gini coefficient, Atkinson index, coefficient of variation; expressed as continuous variables) and working age (25-64 y) or post-working age (>= 65 y) mortality in men and women according to immigration status, accounting for individual and neighbourhood income, and sociodemographic characteristics. Major causes of mortality were examined. Results Relative to low income inequality, high inequality was associated with greater working age mortality in male (HRGini 1.08, 95% CI 1.04 to 1.13) and female (HRGini 1.12, 95% CI 1.06 to 1.18) non-immigrants for all income inequality indictors. Results were similar for female post-working age mortality. There was no relation between income inequality and mortality in immigrants. Among Canadian-born individuals, associations were greater for alcohol-related mortality (both sexes) and smoking-related causes/transport injuries (women). Conclusion Income inequality is associated with mortality in Canadian-born individuals but not immigrants.