Elaboration on the association between immigration and schizophrenia: a population-based national study disaggregating annual trends, country of origin and sex over 15 years

Purpose Generally, immigrant status and male sex are separately documented to increase the risk of schizophrenia; although population-based risk trends by sex and immigration over time have not been examined. This study aims to examine the extent to which immigration acts as a risk factor for schizophrenia, delineated by origin, sex and year, using national population-based data over 15 years. Method Data on all first psychiatric admissions from 1978 to 1992 (n = 10,892) from the National Psychiatric Hospitalization Case Registry of the State of Israel were merged with aggregate national data from the Israeli Central Bureau of Statistics. Results Compared to native-born Israelis, people who migrated prior to the age of 15 (n = 2,335) were at a greater risk of schizophrenia (n = 8,557; RR = 1.6, 95% CI = 1.53; 1.68), particularly those from Far Eastern (RR = 2.43, 95% CI = 1.91; 3.1) and Caribbean and South American (RR = 1.94, 95% CI = 1.51; 2.51) countries. Aggregate risk was higher among female than male immigrants and over the 15-year study immigrationrelated risk declined across the sexes. Conclusion The current findings replicate past research showing that immigrants, particularly from a social minority, as suggested by the social defeat-hypothesis, are at an increased risk of schizophrenia, and extend past findings to show that risk at least in Israel has decreased with time irrespective of sex.