Age at migration and future risk of psychotic disorders among immigrants in the Netherlands: a 7-year incidence study

OBJECTIVE: The purpose of this study was to examine whether the increased risk for developing a psychotic disorder among immigrants is related to their age at the time of migration.

METHOD: In a 7-year first-contact incidence study, immigrants to the Netherlands and Dutch citizens, ages 15-54 years, who made a first contact with a physician for a suspected psychotic disorder were identified. Diagnostic interviews were administered, and DSM-IV diagnoses were determined by consensus between two psychiatrists. A comprehensive municipal registration system provided the denominator, including information on ethnicity and age at the time of migration.

RESULTS: Lower age at the time of migration was associated with a higher incidence of psychotic disorders among immigrants. People who migrated between the ages of 0 and 4 years had the most elevated risk for psychotic disorders compared with the risk among Dutch citizens (age- and sex-adjusted incidence rate ratio=2.96, 95% confidence interval [CI]=2.10-4.17), and the risk gradually decreased with older age at migration (adjusted incidence rate ratio for migration at 5-9 years, 10-14 years, and >29 years, respectively: 2.31 [CI=1.61-3.29], 1.51 [CI=1.02-2.25], and 1.00 [CI=0.58-1.72]).

CONCLUSIONS: The adverse influence of migration on the risk for psychotic disorders is most prominent in early life, suggesting that this is an important period in the etiology of the illness.