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.