THE INFLUENCE OF CLIMATE ON SUICIDAL-BEHAVIOR IN ITALY

A growing number of studies report an asymmetry in the seasonal distri bution of suicides, with a peak in the late spring months for both sex es. The aim of this study is to verify if the climate, apart from its seasonal change, exerts a direct influence on suicidal behaviour. To t his end, deaths by suicide in 17 Italian towns which all have a meteor ologic station have been analyzed, taking into account some climatic i ndicators. Results of analyses show an unequal distribution of suicide s with respect to latitude, with a peak in the North. The distribution of deaths by suicide shows a negative relationship with mean yearly t emperature values, max and min, and with sun exposure indicators, and a positive, but less significant relationship with rainfall values. As far as climatic variables considered as a whole are concerned, stepwi se regression identifies three relevant factors with significant relat ionships to suicide rates: humidity grade, rainfall mean, and sunlight exposure. These three climatic indicators explain up to 63% (Adj R-2) of the variance in the distribution of suicide rates for both genders , with sunlight exposure offering the most significant contribution, w hen regressed on suicide rates via a multiple regression model. Higher suicide rates, therefore, correspond to dry places which are less exp osed to the sun. However, the variable which shows the most significan t correlation with suicide rates for both sexes is not a climatic one, but the percentage of the population aged 65 and over. The distributi on of people at greater biological risk for possible disruption of bra in neurochemistry (i.e, older people), therefore, predicts the distrib ution of suicide rates. Climate contributes to this biological risk by modifying both the responsiveness of the circuits that control mood a nd behaviour, and also the frequency and intensity of social interacti on. (C) 1998 Elsevier Science Ireland Ltd.