Season of birth in suicides: excess of births during the summer among schizophrenic suicide victims.

BACKGROUND

Season of birth is associated with several psychiatric disorders and suicidal behavior. We explored the association between the season of birth and suicide among schizophrenic and psychotic suicide victims.

METHODS

The study sample consisted of all suicides in the province of Oulu in Northern Finland from 1989 to 2010. Causes of death were extracted from death certificates, and psychiatric diagnoses associated with the hospital treatments were obtained from the Finnish Hospital Discharge Register. The seasons were defined as follows: winter (from November to January), spring (from February to April), summer (from May to July), and autumn (from August to October). Suicide victims (n = 1,902) were categorized as having either schizophrenia (n = 228) or psychosis other than schizophrenia (n = 240). Suicide victims without any hospital-treated mental disorder (n = 1,434) were used as a comparison group.

RESULTS

The distribution of births among suicide victims with schizophrenia differed statistically significantly from that observed in the general population, with a peak in summer (OR 1.2, 95% CI 1.0-1.5).

CONCLUSIONS

Birth during summer may predispose schizophrenic persons to suicide. The putative roles of serotonin, dopamine, and vitamin D status in the season of birth of psychotic suicide victims are discussed.