Abstract
It has been suggested that winter birth in urban areas may be associated with an increased risk of schizophrenia. Data on 4139 patients with a hospital diagnosis of schizophrenia were obtained from a survey of public departments of psychiatry in metropolitan France. Place of birth was classified according to the administrative subdivision of French territory into 95 ‘ départements’. Density of population in the decade and in the département of birth was identified using successive census data. A 20% excess (OR, 1.20; 95% CI, 1.03–1.40; p = 0.02) of winter births (January–March) was found among patients born in highly densely populated areas (> 136 inhabitants/km 2) compared to those born in other areas. These results suggest that seasonal early environmental risk factor(s) linked to schizophrenia predominantly operate in urban areas.
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