Schizophrenia: increased risk associated with winter and city birth--a case-control study in 12 regions within England and Wales.

In a recent Swedish study, Lewis et al' found that the risk of schizophrenia was greater in people brought up in cities than in those brought up in rural areas.The factors re- sponsible for this effect are uncertain but a winter birth excess has been consistently re- ported in schizophrenia.2We suggest that the same factors are responsible for both the urban/ rural difference in risk and the winter birth excess.We predict (a) winter birth and urban birth are each associated with an increased risk of schizophrenia; and (b) the effects of winter birth and urban birth potentiate each other.summer showed no city birth effect (OR 1 -01).