Month of birth and suicide: An exploratory study

To explore the association between suicide and month of birth.

Data were extracted from records of the Public Health Department in North Cheshire between 1989 and 2000. ¤ Suicide' refers to all deceased who were the subjects of coroner's inquests resulting in a verdict of suicide or an open verdict. The month of birth of all who died of natural causes and were reported during a 2-year period was obtained from the Public Health Department in North Cheshire for comparison.

There were 502 incidents of suicide in North Cheshire during the 12-year period. Significant differences were found between suicides and deaths due to natural causes, with an increase of incidents of suicide in those born in the month of May ( h 2 23, d.f.11, P < 0.01). The distribution of suicide by hanging appeared to be significantly higher in those born in September and July and lowest in those born in November compared with what would expected by chance ( h 2 28, d.f.11, P < 0.005). Those who died by violent means were more likely to have been born in the summer. The difference between the observed and expected numbers of suicides by methods other than hanging failed to reach statistical significance.

The results, though inconclusive, are interesting, particularly in view of recent reports that persons born during the winter - spring months had significantly lower values of 5-HIAA, and also reports of low CSF levels of 5-HIAA in persons with violent suicidal behaviour such as hanging, stabbing, firearms, or jumping from heights and impulsivity. A biological explanation of suicidal behaviour could have implications for our understanding of the psychopathology of suicide and eventually offer new strategies for treatment and prevention. The conflicting reports from different countries within the northern hemisphere indicate the need for future studies with adequate design and acceptable statistical power.