Depression and Type 2 Diabetes Over the Lifespan
OBJECTIVE— It has been argued that the relationship between depression and diabetes is
bi-directional, but this hypothesis has not been explicitly tested. This systematic review examines
the bi-directional prospective relationships between depression and type 2 diabetes.
RESEARCH DESIGN AND METHODS— A search was conducted using Medline for
publications from 1950 through 2007. Reviewers assessed the eligibility of each report by
exposure/outcome measurement and study design. Only comparative prospective studies of
depression and type 2 diabetes that excluded prevalent cases of depression (for diabetes predicting
depression) or diabetes (for depression predicting diabetes) were included. Two sets of
pooled risk estimates were calculated using random effects: depression predicting type 2 diabetes
and type 2 diabetes predicting depression.
RESULTS— Of 42 full-text publications reviewed, 13 met eligibility for depression predicting
onset of diabetes, representing 6,916 incident cases. Seven met criteria for diabetes predicting
onset of depression, representing 6,414 incident cases. The pooled relative risk (RR) for
incident depression associated with baseline diabetes was 1.15 (95% CI 1.02–1.30). The RR for
incident diabetes associated with baseline depression was 1.60 (1.37–1.88).
CONCLUSIONS— Depression is associated with a 60% increased risk of type 2 diabetes.
Type 2 diabetes is associated with only modest increased risk of depression. Future research
should focus on identifying mechanisms linking these conditions.