Seasonal variation in suicidal deaths in Chile: Its relationship to latitude

Abstract

Background: Studies in the northern and southern hemispheres consistently identified seasonal influences on monthly and semester suicide distribution. The variations of sunlight exposure in zones of increasing latitude has been suggested as one of the most plausible explanations for this phenomenon. Some recent studies in the northern hemisphere could not find seasonal asymmetries of suicides. The current study examines the monthly, seasonal and semester distribution of suicidal deaths in Chile and the influence of seasons in zones of low latitude as compared with regions of high or very high latitude, trying to determine if a seasonal pattern still exists in a country of the southern hemisphere. Methods: Monthly, seasonal and semester suicidal data over the period 1995-1999 were examined for the whole sample and for gender-specific subgroups in Chile. Four different latitudinal zones were analyzed separately, in order to investigate the effect of the photoperiod on suicide distribution. Results were analyzed by chi(2) tests for multinomials, as an overall measure of deviation. Results: We found a significant unimodal springtime peak for both genders in the global territory. Among the 4,710 male and 829 female suicides reported in this period there were no gender differences in the seasonal pattern of suicidal deaths. When divided into four different latitudinal zones, the regions with low latitude ( north of the country) showed no significant differences, while central and southern zones ( higher latitude) show a significant springtime pattern. In the extreme south of the country, no significant differences were found, probably due to the very small number of cases. Conclusion: The study confirms the existence of a unimodal springtime peak of suicides in Chile, but not in the zone of low latitude. Results support the notion that the seasonal impact on suicidal distribution is a function of photoperiod.