Migration and mortality: a 20 year follow up of Finnish twin pairs with migrant co-twins in Sweden

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Abstract
Study objective: Finland has a higher mortality overall and for major causes of death than Sweden, primarily in men. The objective of this study was to analyse mortality in migrants from Finland to Sweden. Design: A longitudinal study based on the Finnish Twin Cohort Study. Information about migration from Finland to Sweden, duration of stay in Sweden for the migrants, and deaths 1976–1995 was obtained from national registers. Observed numbers of deaths in migrants were compared with expected numbers based on the age standardised mortality experience of the Finnish Twin Cohort. First deaths in migrants and non-migrants of migrant discordant pairs were compared controlling for genetic and early childhood factors. Participants: Twin pairs of the Finnish Twin Cohort Study where at least one twin had migrated to Sweden (1542 twin pairs). Main results: Among men, migrants from Finland to Sweden showed an overall similar mortality compared with all subjects of the Finnish Twin Cohort (SMR 1.1; 95% CI 0.9 to 1.4). Mortality from non-violent causes was increased for migrants with at most 20 years in Sweden (SMR 1.9; 95% CI 1.2 to 2.6) and decreased in those with a longer stay (SMR 0.7; 95% CI 0.4 to 0.9). Similar results were obtained concerning first deaths in twin pairs discordant for migration. Among women, migrants had an increased mortality overall (SMR 1.4; 95% CI 1.0 to 1.8), from cardiovascular disease (SMR 1.7; 95% CI 1.0 to 2.7), and from violent causes (SMR 2.5; 95% CI 1.2 to 4.6) compared with all women of the Finnish Twin Cohort. In analyses of migrant discordant pairs only first deaths from cardiovascular disease tended to be more common in the migrants than in non-migrant co-twins. Conclusions: Migrants from Finland to Sweden seem to have an overall mortality comparable to that prevailing in Finland suggesting no strong influence on mortality by the migration. Duration of stay seems to be associated with mortality in the migrants, at least in men, with a lower mortality after several years in Sweden.