Synchronized annual rhythms in violent suicide rate, ambient temperature and the light-dark span.

To investigate whether violent and nonviolent suicide and homicide are related to atmospheric or geomagnetic activity, we investigated the relationships between weekly number of suicides or homicides for all Belgium for the period 1979-1987, and ambient temperature, relative humidity, air pressure, hours of sunlight and precipitation per day, wind speed and geomagnetic index. The occurrence of violent suicide was significantly and positively related to ambient temperature, sunlight duration, an increase in temperature over the few past weeks, and negatively to relative humidity. Higher ambient temperature and an increase in air temperature over the few past weeks were the most significant climatic predictors of violent suicide rate. A highly significant common annual rhythm with a common acrophase of 190 degrees was detected in violent suicide rate, ambient temperature and sunlight duration. No significant time-relationships between nonviolent suicide or homicide and any of the weather variables were found. It is concluded that i) violent suicide may be related to short-term fluctuations in the weather and in particular to temperature; and ii) the annual rhythm in violent suicide may be synchronized by the annual rhythms in ambient temperature and light-dark span.