Sex differences in depression: a role for preexisting anxiety.

The role of anxiety disorders in the development of sex differences in major depression is analyzed. Data come from a longitudinal epidemiologic study of young adults in the Detroit, Michigan area. The Diagnostic Interview Schedule, revised according to DSM-III-R, was used at baseline to measure lifetime psychiatric disorders and at follow-up to measure psychiatric disorders during the 3.5-year interval since baseline assessment. Consistent with previous reports, the lifetime prevalence of major depression was nearly two-fold higher in females than in males. The sex difference was primarily in major depression comorbid with anxiety disorders. Results from Cox-proportional hazards models, with time-dependent covariates, showed that prior anxiety disorder increased the risk for subsequent major depression in both sexes, with no evidence of an interaction. History of anxiety disorder, including number of prior anxiety disorders, accounted for a considerable part of the observed sex difference in major depression. Controlling for prior anxiety reduced by more than 50% the coefficient that estimates the association between gender and major depression. The results suggest that the higher occurrence of anxiety disorders in females than males beginning early in life might explain in large part the higher female risk for major depression. They emphasize the need for further research on sex differences in anxiety disorders.