Mental Disorder and Season of Birth

A National Sample Compared with the General Population

¹ Bethlem Royal and the Maudsley Hospitals, London, SE5 8AZ
² Department of Psychological Medicine, University of Newcastle upon Tyne, Newcastle upon Tyne, NE1 4LP
³ Institute of Psychiatry, London, SE5 8AF

1. The season-of-birth distribution, by diagnosis, has been examined for 46,000 psychiatric patients. The patients were all those with a first-ever admission to a psychiatric bed in England and Wales during the years 1970 or 1971 and who had been born in England and Wales during the years 1921-55. Their quarterly distribution of birth was compared, on a year-by-year basis, with that of all live births in England and Wales.

2. For schizophrenia and for manic-depressive psychosis there was a highly significant excess of births in the first quarter of the year. This excess was particularly marked for patients diagnosed as manic. For the other diagnostic groups, the numbers born in the first quarter of the year differed only very slightly from expectation. There was a significant excess in the first quarter of the year for patients diagnosed as psychotic depression compared with those diagnosed neurotic depression.

3. Possible explanations for the findings are considered, and it is concluded that the evidence for a meaningful association between season of birth and functional psychosis is now sufficiently strong to warrant more detailed study.