Influence of environmental factors on suicidal behavior.

The regional distribution of completed suicide was analyzed in 19 regions of France for the years 1975 and 1983. The regional distributions of environmental variables (ambient temperature, sunlight duration, and precipitation) and of sociological factors (social cohesion, socioeconomic status, status of women, and social support) were then correlated using Pearson coefficients, stepwise regression analysis, and partial correlations. Our main finding is that environmental factors such as ambient temperature may play a role in the regional distribution of completed suicide in France. Both the stepwise regression analysis and the controlled regression analysis revealed that, among all the variables studied (environmental and sociological), the main factors affecting the regional distribution of suicide were ambient temperature and sunlight duration. To our knowledge, this is the first detailed study demonstrating a clear relationship between environmental variables and suicidal behavior. The finding may be consistent with the recent description of forms of affective disorders occurring in relationship to environmental factors.