Annual rhythms of violence in hospitalized affective patients: correlation with changes in the duration of the daily photoperiod

We extensively reviewed the medical records of violent patients restrained in a locked psychiatric ward of a university‐based hospital for 6 years (1980‐1985). A total of 551 patients were restrained at least once during hospitalization, of which 186 patients had affective disorders and 365 had nonaffective psychiatric illnesses. While the number of restrained non‐affective patients was constant throughout the year, the number of restrained affective patients showed a circannual rhythm with nadirs in May and November and peaks in June and December. This pattern of restraints correlated to changes in the length of daily sunlight (photoperiod). These results suggest that the aggressiveness of patients with affective disorders correlates with photoperiod duration and that the aggressiveness of patients with nonaffective disorders does not correlate with photoperiod.