Seasonal affective disorder and latitude: a review of the literature

Background: The aim of the study is to investigate the relationship between the prevalence of SAD and latitude. Methods: An overview of the epidemiological literature on the prevalence of SAD is given and studies relevant for the latitudinal dependency of prevalence will be analyzed and discussed. Results: The mean prevalence of SAD is two times higher in North America compared to Europe. Over all prevalence studies, the correlation between prevalence and latitude was not significant. A significant positive correlation was found between prevalence and latitude in North America. For Europe there was a trend in the same direction. Conclusions: The influence of latitude on prevalence seems to be small and other factors like climate, genetic vulnerability and social-cultural context can be expected to play a more important role. Additional controlled studies taking these factors into account are necessary to identify their influence. (C) 1999 Elsevier Science B.V. All rights reserved.