Season of birth in suicidology : neurobiological and epidemiological studies

Background: Several neuropsychiatrie disorders have shown season of birth associations. Low cerebrospinal fluid (CSF) levels of the serotonin metabolite 5-HIAA and the dopamine metabolite HVA have been associated with suicidal behaviour, impulsivity, and aggression. This thesis investigated associations between the season of birth, the CSF levels of three monoamine metabolites (including MHPG of norepinephrine), the scales of the diagnostic interview for borderline patients (DIB), and psychiatric diagnoses. Also, the methods of suicide were investigated in relation to the season of birth. Methods: We studied a clinical sample of 241 patients in Stockholm with mood, anxiety and adjustment disorders with respect to the CSF levels of monoamine metabolites in relation to the season of birth, and in relation to the DIB in an overlapping sample. We also analysed all completed suicides during the 42 years 1952- 1993inVästerbottenin northern Sweden (1466 cases) by multiple logistic regressions to relate suicide methods with season of birth, gender, age, urban-rural residence, marital status, year of suicide, and season of suicide. For the 20 years 1961- 1980 (693cases), psychiatric in-patient and out-patient records were also examined for any history of psychiatric contacts and psychiatric diagnoses. In two mutually independent samples, we investigated the DIB in relation to the season of birth. Results: In the Stockholm sample, those born during February to April had significantly lower CSF levels of 5-HIAA, and those born during October to January had significantly higher CSF levels of HVA, HVA/5-HIAA, and HVA/MHPG, as well as (non-significantly) higher levels of 5-HIAA. Those with an intermediate score of section II (impulse action patterns) of the DIB had significantly higher CSF levels of 5-HIAA and HVA, and they were significantly more likely to have been born during October to January. In the Västerbotten register, those born during February to April were significantly more likely to have preferred hanging rather than poisoning or petrol gases, and conversely for those born during October to January. These associations with suicide methods were found for the total sample and for those without any history of psychiatric contacts, but not for those with psychiatric contacts. Conclusions: Suicidal behaviour shows statistically significant variation according to the season of birth, most probably mediated by a variation in an independent trait of vulnerability to suicide based on neurodevelopmental parameters, particularly the serotonergic system. The suicidal process differs between those who seek psychiatric care compared to those who do not, reflecting differences in the diagnostic spectra and in the extent of mental illness.Härtill 6 delarbeten.