Differential mortality rates in major and subthreshold depression: meta-analysis of studies that measured both

Background: Although the association between depression and excess mortality has been well established, it is not clear whether this is greater in major depression than in subthreshold depression. Aims: To compare excess mortality in major depression with that in subthreshold depression. Method: We searched bibliographic databases and included prospective studies in which both major and subthreshold depression were examined at baseline and mortality was measured at follow-up. Results: A total of 22 studies were included. People with major depression had a somewhat increased chance of dying earlier than people with subthreshold depression but this difference was not significant, although there was a trend (relative risk 1.13, 95% CI 0.98-1.30, P = 0.1). The population attributable fraction was 7% for major depression and an additional 7% for subthreshold depression. Conclusions: Although excess mortality may be somewhat higher in major than in subthreshold depression, the difference is small and the overall impact on excess mortality is comparable.