Intermarriage and mortality among Finnish migrants in Sweden: a prospective register study using binational data.

Conjugal ties may contribute to a convergence of health behaviours between migrants and natives, but the association between intermarriage and health outcomes remains understudied. We investigated mortality patterns among Finnish migrants in Sweden according to the spouse's country of birth and compared these patterns with those observed in the native populations of both Sweden and Finland. Leveraging register data from Sweden and Finland, we identified all married Finnish migrants aged 40-64 and their spouses in Sweden in 1999 and corresponding reference groups in both countries. We used a combination of direct matching and inverse probability weighting to adjust for sociodemographic differences between the groups. We followed individuals for all-cause, alcohol-related, smoking-related, and cardiovascular disease (CVD) mortality during 2000-17. Accounting for sociodemographic characteristics, Finnish migrant men married to Swedish-born as opposed to Finnish-born spouses showed lower all-cause [incidence rate ratio (IRR) 0.94, 95% confidence interval (CI) 0.90-0.98], and CVD mortality (IRR 0.88, 95% CI 0.81-0.95), levels more akin to native Swedes. Migrant women with Swedish-born spouses instead had higher smoking-related mortality (IRR 1.41, 95% CI 1.24-1.61) than those married to Finnish-born spouses, mirroring the higher smoking-related mortality of native Swedish women. Individual-level regression analysis on migrants further indicated lower alcohol-related mortality for intermarried men, adjusted for duration of marriage (IRR 0.74, 95% CI 0.56-0.98). These findings suggest that intermarriage with a native spouse can facilitate the convergence of health behaviours and behaviour-related mortality between migrants and natives.