Why do people with anxiety disorders become depressed? A prospective-longitudinal community study.

Objective: To examine the temporal relationships of anxiety and depressive disorders, their risk factors and to explore why people with anxiety develop depression.

Method: Data from an original 4-5-year prospective-longitudinal community study (N= 3,021) of adolescents and young adults with DSM-IV anxiety and depressive disorders identified with the Composite International Diagnostic Interview are used to examine risk factors, as well as course and outcome.

Results: (i) Anxiety disorders, except for panic disorder, are almost always primary conditions. (ii) Over the follow-up period, rates of comorbid anxiety-depression increased substantially and resulted in increased impairment and disabilities. (iii) Predictors for first onset of 'pure' depressive and 'pure' anxiety disorders revealed recognizable differences. (iv) Baseline clinical characteristics of anxiety disorders were significantly associated with an increased risk to develop major depression over the follow-up period.

Conclusion: Findings suggest that most anxiety disorders are primary disorders that substantially increase the risk for secondary depression.