Income mortality paradox by immigrants' duration of residence in Sweden: a population register-based study.

Background: Studies have shown that, compared with the general native population, immigrants display weaker or absent income gradients in mortality. The aim of this study is to examine the extent to which the income gradient is modified by immigrants' duration of residence in Sweden.

Methods: Swedish register data from 2004 to 2016 were used to study the association between individual income and all-cause mortality among foreign-born and Swedish-born individuals at ages 25-64 years. Based on relative indices of inequality (RIIs) and slope indices of inequality (SIIs) derived from Poisson regressions, we measured relative and absolute mortality differentials between the least and most advantaged income ranks. The analyses were stratified by sex, immigrants' European or non-European origin, and immigrants' duration of residence in Sweden.

Results: The relative income inequality in mortality among immigrant men was less than half (RII: 2.32; 95% CI: 2.15 to 2.50) than that of Swedish-born men (RII: 6.25; 95% CI: 6.06 to 6.44). The corresponding RII among immigrant women was 1.23 (95% CI: 1.13 to 1.34) compared with an RII of 2.75 (95% CI: 2.65 to 2.86) among Swedish-born women. Inequalities in mortality were lowest among immigrants who resided for less than 10 years in Sweden, and most pronounced among immigrants who resided for more than 20 years in the country. Corresponding analyses of absolute income inequalities in mortality based on the SII were largely consistent with the observed relative inequalities in mortality.

Conclusions: Income inequalities in mortality among immigrants differ by duration of residence in Sweden, suggesting that health inequalities develop in the receiving context.