Dutch and Chinese researchers conducted systematic searches of PubMed, PsycINFO, and Embase. Studies were included if depression was measured with a standardized instrument and mortality was reported for both depressed and nondepressed participants at follow-up. A total of 293 studies including 1,813,733 participants (135,007 depressed and 1,678,726 nondepressed) from 35 countries were included. The overall unadjusted relative risk of mortality in depressed relative to nondepressed participants was 1.64. This statistic declined somewhat when the researchers adjusted for possible methodological problems in the studies.
With the exception of chronic obstructive pulmonary disease, they found no strong indications that the risk of death was different across relatively healthy community samples and specific patient samples with heart disease, cancer, kidney disease, or other disease. That suggests that generic factors associated with the biology of depression—not disease-specific factors—are responsible for the higher death risk.
“Our observation that the association between depression and mortality is not strikingly different between community-based samples and patient samples suggests that the association between depression and mortality may be explained better by generic mechanisms, such as biological dysregulations and lifestyle factors that have a general impact on health, than by disorder-specific mechanisms…” they concluded.
For more information on the association between mental illness and mortality risk, see the Psychiatric News article, “Mental Illness Linked to Premature Death in Epilepsy Patients."