Influence of climate on the prevalence of mania

Monthly rates of admission of manic patients to the Department of Psychiatry in Galway Regional Hospital were examined for a five-year period. Monthly variation in admission rates was compared with monthly levels of sunshine, temperature and daylength. Results indicated a significant seasonal variation in the prevalence of mania: admission rates were higher in the sunnier months and in months with a greater average daylength. It is suggested that the presentation of mania in this fashion is due to an abnormal response to light in these patients.