The impact of migration in all-cause mortality: the Turin Longitudinal Study, 1971-2005

North-western Italy has a long history of domestic influx, however little is known on how migrant mortality compares to mortality at the local level. While geographic mortality gradients may play a role, conceptualizations developed for international migration may also be relevant. Using this theoretical framework, the study investigated immigrant-native differentials in the north-western city of Turin through a 34-year follow-up that was facilitated by the Turin Longitudinal Study. The study population comprised inhabitants of age 30-74 years at the 1971 census. Survival trajectories were modelled through the Gompertz distribution and were examined for nativity status, birthplace, length of stay and age at arrival (the last two variables were combined). All estimates were adjusted for socio-economic factors. Overall, the risk of dying for internal migrants was lower, compared to locals, and consistent with geographic gradients. However, this pattern hid significant differences mediated by both age at arrival and length of stay. The advantage appeared to be exclusive to young and adult migrants, despite differentials narrowing over time. Immigrants who arrived after age 44 suffered instead a progressively greater excess risk, compared to natives, as residence increased. The dissipation of the health advantage found in internal migrants, along with poor health outcomes amongst people older at arrival, raises concern about immigrants from developing countries who need to endure a more demanding journey and adjustment to the new environment. The study indicated, through lengthy longitudinal data, that immigrant-native differentials were best explained by the stratified variable 'length of stay by age at arrival' and this should inform future studies.