Circadian variation in attempted suicide by deliberate self-poisoning

Circadian patterns have been shown for many physiological variables and several medical diseases. We studied prospectively all patients who attempted suicide by deliberate self poisoning and were admitted to the accident and emergency department of St Anna Hospital, Ferrara, from 1 January 1989 to 31 December 1991. Seventy one patients were men and 141 women. The time of self poisoning was categorised into 24 increments of one hour, and data were analysed by cosinor analysis. A significant circadian rhythm was found for the whole population (p = 0.007), and for men (p = 0.007) and women (p = 0.026). The acrophases were respectively 17:45, 18:37, and 17:16. Our results suggest that the risk of attempting suicide is greatest in the early evening.