SEASONALITY OF BIRTH IN SCHIZOPHRENIA - THE EFFECT OF REGIONAL POPULATION-DENSITY

It has been suggested that winter birth in urban areas may be associat ed with an increased risk. of schizophrenia. Data on 4139 patients wit h a hospital diagnosis of schizophrenia were obtained from a survey of public departments of psychiatry in metropolitan France. Place of bir th was classified according to the administrative subdivision of Frenc h territory into 95 'departements'. Density of population in the decad e and in the departement of birth was identified using successive cens us 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 ot her areas. These results suggest that seasonal early environmental ris k factor(s) linked to schizophrenia predominantly operate in urban are as.