Age of migration and common mental disorders among migrants in early adulthood: a Norwegian registry study

Younger age of migration is associated with higher risk of psychotic disorders but the relationship between age of migration and common mental disorders is less clear. This study investigates the association between age of migration and diagnosed common mental disorders among migrants living in Norway. Using national Norwegian register data from 2008 to 2019, we compared the odds of a common mental disorder diagnosis in healthcare services during early adulthood among non-migrants, descendants and migrants with different ages of migration and lengths of stay. We also investigated differences in the relationship for different migrant groups and for men and women. Descendants and childhood migrants with ≥ 19 years in Norway had higher odds of common mental disorders than non-migrants, while those migrating during adolescence with ≥ 19 years in Norway had similar odds. Those migrating during emerging and early adulthood had lower odds. Overall among migrants, the relationship between age of migration and common mental disorders was more pronounced for migrants < 19 years in Norway than ≥ 19 years and for non-refugees compared with refugees, especially men. Descendants and childhood migrants with long stays may have higher odds of common mental disorders due to the associated stress of growing up in a bicultural context compared with non-migrants. Age of migration has a negative association with diagnosed common mental disorders but much of this effect may attenuate over time. The effect appears weaker for refugees, and particularly refugee men, which may reflect higher levels of pre-migration trauma and stress associated with the asylum-seeking period for those arriving as adults. At the same time, migrants, especially those arriving as adults, experience barriers to care. This could also explain the particularly low odds of diagnosed common mental disorders among adult migrants, especially those with shorter stays.