Season of birth in schizophrenia: no latitude at the equator

Background If the established winter excess in births of people who subsequ ently develop schizophrenia is an effect of 'seasonality', this would be te stable by examining the pattern of births in an equatorial region with no f ormal seasons. Aims To investigate whether there is any variation in month of birth among patients from equatorial Singapore with a diagnosis of schizophrenia. Method All 9655 patients discharged from Singapore's national psychiatric h ospital with a diagnosis of schizophrenia were included (year of birth rang e 1930-1984). We analysed aggregated data, as well as the data of subsample s grouped according to birth-year periods, in,order to examine secular tren ds. One patient subsample (those born 1960-84) allowed exact matching again st the general population data set and close testing of any seasonal influe nce. Results Monthly variation in births was evident for both patients and contr ols; the patterns were very similar, apart from the patient sample showing a trough in March-April. Conclusions In an equatorial region, where 'seasons' are absent, no seasona l excess in births of those later developing schizophrenia was evident. Declaration of interest Funded by the institute of Mental Health, Singapore .