An interesting 2006 study by Emad Salib and Mario Cortina-Borja examined the potential link between suicide and season of birth. Previous studies have revealed seasonal birth trends for such diseases as lymphoblastic leukemia, early onset non-Hodgkin's lymphoma, breast cancer and Crohn's disease among others. In terms of mental illness, one study found that more patients with Alzheimer's and schizophrenia were born in December and January whereas affective disorders, alcoholism, autism, and dyslexia are more frequently reported in those born in spring or summer months (Salib & Cortino-Borja, 2006). For this reason and because few studies have looked at suicide and birth season, Salib and Cortino-Borja sought to examine the possible link between the two phenomenon. Some studies have identified July as a particular month linked with suicide while other studies say winter has ties to an increased risk for suicide (Salib & Cortino-Borja, 2006).
In this study, the researcher used routinely collected suicide data over a 22-year period in England and Wales. This particular research exceeded previous attempts to examine the same question as its sample size was substantially greater with 27,000 suicides included from over 11 million births.
Salib and Cortino-Borja (2006) hypothesized that the risk of suicide would vary according to month of birth and that the association would remain even after controlling for the effects of the total number of births per month in the population. They also predicted that there would be a difference in birth month when specifically looking at suicide by gender and method (violent vs. non-violent). An example of a violent method of suicide would be a gunshot wound while non-violent suicide could be an overdose.
According to the result of this study, there is a 17% increase of suicide for people born in the spring and early summer compared to those born in autumn; this number is greater for women than for men. When split by gender, men born in late spring were at increased risk of suicide while the same was true for women born in midsummer. For suicides by men, the monthly birth rate peaks were in spring for violent methods and summer for non-violent methods. For women, the peaks were in late spring for both methods (Salib & Cortino-Borja, 2006). The researchers' hypotheses regarding the link between seasonality and suicide were confirmed.
The authors concluded that this line of research is important as the etiology of suicide is multifaceted; all aspects of this phenomenon should therefore be studied in order to conceptualize the life trajectory of someone likely to commit suicide better. Seasonality as it relates to suicide has been explained by weather conditions and their effect on the central nervous system. Despite these findings, one cannot say for certain that birth month is related to suicidal tendencies (or alcoholism or autism)., because the issue is so complex . This study in particular was limited as it did not consider co-morbid psychiatric illnesses, religion, race/ethnicity, and socioeconomic status. The subset of people for which the link between seasonality and suicide holds true may be even smaller that what Salib and Cortino-Borja (2006) found. Still, it is interesting to note the varying formulations used to explain a very tragic occurrence.
Citation:Salib, E. & Cortino-Borja, M. (2006). Effect of month of birth on the risk of suicide. British Journal of Psychiatry, 188, 416-422.