Abstract
Several studies have confirmed seasonal variation in suicide rates according to hours of sunshine. The suicide pattern was assessed in São Paulo, southeastern Brazil, at the tropic of Capricorn from 1996 to 2004. Poisson regression was employed to estimate parameters of seasonality, as well as to verify associations for each day between daylight duration and suicide. During the nine-year study period, there were 3,984 suicides (76.9% in men; median age=38.7 years old). Seasonal averages of suicides were similar, as were monthly averages. Poisson regression did not reveal any association between suicide rates and hours of sunshine (p=0.45) for both sexes. In conclusion, no seasonal pattern was observed for suicides.
Highlights
In his masterpiece, “Suicide,” Emile Durkheim noted that “when the days grow longer quickly, suicides increase greatly,” i.e., suicide has a peak in the spring or summer and a trough in winter, which has been confirmed in studies conducted in the Northern Hemisphere.[4,5] few studies have addressed this issue in the Southern Hemisphere, their findings were similar.[2]
Seasonal suicide averages had similar distribution according to seasons as were monthly averages
Poisson regression showed no association between number of suicides by day and direct solar irradiance (p=0.45)
Summary
“Suicide,” Emile Durkheim noted that “when the days grow longer quickly, suicides increase greatly,” i.e., suicide has a peak in the spring or summer and a trough in winter, which has been confirmed in studies conducted in the Northern Hemisphere.[4,5] few studies have addressed this issue in the Southern Hemisphere, their findings were similar.[2] They have shown that higher suicides rates occur during months with more daily sunlight hours. In Singapore (at the Equator line), a country with little daily sunlight variation throughout the year, there are no seasonal fluctuations of suicide rates.[3] These studies suggest that sunshine-regulated hormones, such as melatonin, may have a role in triggering suicide.
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