Season of birth variations in suicide methods in relation to any history of psychiatric contacts support an independent suicidality trait

Abstract

Background: Due to reports on season of birth variations in suicidal behaviour as well as in cerebrospinal fluid levels of monoamine metabolites, we investigated season of birth variations in suicide methods for completed suicides in relation to any history of psychiatric contacts. Relationships with the psychiatric diagnoses for those with psychiatric contacts were also studied. Methods: Sociodemographic variables and suicide methods were examined for all the 693 suicide victims during 1961–1980 in Västerbotten, Sweden. Information on any history of psychiatric contacts was obtained from psychiatric in-patient and out-patient records. Results: Gender differences in the choice of suicide method were found in the group without any history of psychiatric contacts, but not in those with such a history. Only those without a history of psychiatric contacts showed season of birth variations for suicide methods — those born during February to April were significantly more likely, and those born during October to January significantly less likely, to have preferred hanging rather than poisoning or petrol gases. These associations were stronger for the determined suicides, for males, and for urban residence. Suicide victims with a history of psychiatric contacts were significantly younger than those without. Limitations: No psychological autopsies for those without psychiatric contacts. No information on eventual contacts with general practitioners. No measures of monoamine neurotransmitters were available. Conclusions: Season of birth association for suicide methods is likely to be mediated by a suicidality trait independently of specific major psychiatric disorders. Monoamine neurotransmitters, particularly serotonin, are likely to underlie such a trait.