URBANIZATION AND PSYCHOSIS - A STUDY OF 1942-1978 BIRTH COHORTS IN THE NETHERLANDS

Background. Urban birth is associated with later schizophrenia. This s tudy examined whether this finding is diagnosis-specific and which ind ividuals are most at risk. Methods. All live births recorded between 1 942 and 1978 in any of the 646 Dutch municipalities were followed-up t hrough the National Psychiatric Case Register for first psychiatric ad mission for psychosis between 1970 and 1992 (N = 42115). Results. Urba n birth was linearly associated with later schizophrenia (incidence ra te ratio linear trend (IRR), 1.39; 95 % confidence interval (95 % CI), 1.36-1.42), affective psychosis (IRR, 1.18; 95 % CI, 1.15-1.21) and o ther psychosis (IRR, 1.27; 95 % CI, 1.24-1.30). Individuals born in th e highest category of the three-level urban exposure were around twice as likely to develop schizophrenia. Associations were stronger for me n and for individuals with early age of onset. The effect of urban bir th was also stronger in the more recent birth cohorts. Conclusions. Th ere are quantitative differences between diagnostic categories in the strength of the association between urban birth and later psychiatric disorder. High rates of psychosis in urban areas may be the result of environmental factors associated with urbanization, the effect of whic h appears to be increasing over successive generations.