Migration as a risk factor for schizophrenia: a Danish population-based cohort study.

BACKGROUND A growing body of evidence suggests that migration is a risk factor for the development of schizophrenia, although the putative mechanism remains obscure. AIMS To examine immigrant background and history of foreign residence as risk factors for schizophrenia. METHOD Using data from the Danish Civil Registration System, we established a population-based cohort of 2.14 million persons resident in Denmark by their fifteenth birthday. Schizophrenia in cohort members and parental psychiatric disorder were identified by cross-linkage with the Danish Psychiatric Case Register. RESULTS The relative risk of developing schizophrenia was 2.45 (95% Cl 2.25-2.67) and 1.92 (95% Cl 1.74-2.12) among first- and second-generation immigrants respectively, and 1.60 (95% Cl 1.25-2.05) among Danes with a history of foreign residence. CONCLUSIONS Migration confers an increased risk for schizophrenia that is not solely attributable to selection factors and may also be independent of foreign birth.