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 (HR(Gini) 1.08, 95% CI 1.04 to 1.13) and female (HR(Gini) 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.