Season of birth associated with the age and method of suicide

A recent study reported season of birth variation in CSF levels of 5-HIAA and HVA, with low 5-HIAA for February to April and high HVA for October to January (Chotai & Åsberg, 1999). We therefore analysed data on all completed suicides during 1952--1993 in the county of Västerbotten in northern Sweden (1466 cases), regarding these birth seasons in relation to suicide method and sociodemographic variables. Those with suicide age under 45 years were more likely than older suicides to have been born during February to April, significantly so compared to October to January. This was more pronounced for the later birth-year cohort (born in 1931 or later). Those who preferred hanging rather than poisoning or petrol gases were significantly more likely born during February to April. Those who preferred poisoning rather than hanging were significantly more likely born during October to January, particularly for the later birth-year cohort. The results regarding suicide method were somewhat more pronounced for males. The results of the study are compatible with a hypothesis of season of birth variation in CSF monoamine metabolites.