Seasonal variation of suicide in South Africa

Nationally registered suicide mortality data for 1980-1989 were studied to determine whether the internationally observed seasonal variation in suicide incidence, with a spring/summer peak and winter trough, is present in South Africa; and if selected demographic variables influence these seasonal trends. The total number of deaths in a particular month in all ten years was analyzed. Log-linear modeling was performed to investigate the effect of sex, age, race, and month on suicide counts. Age was grouped in ten-year categories. Goodness of fit of the model was measured by the Pearson Chi-squared statistic. There were 16,389 deaths ascribed to suicide in the study period. There was a significant monthly effect with a peak in spring/summer and a trough in winter. This effect was independent of sex and age. The winter trough and summer peak were relatively more pronounced for blacks and Coloreds than for Asians and whites. The findings are consistent with international trends. The fact that the expected pattern was more pronounced for Coloreds and blacks could partly be related to their being less urbanized. This could result in their being less likely to spend time indoors, which would increase their exposure to seasonal variation in climatic variables. Hence, they may experience greater circannual rhythms in biochemical processes that are associated with vulnerability or resistance to stressors. There is evidence that these processes may involve dopamine, serotonin, or melatonin metabolism, which have been hypothesized to account for seasonal variation in suicide incidence.