Does depression increase the risk of developing type 2 diabetes?

Background Members of a scheme awarding injury pensions may allege that the onset of diabetes was precipitated or caused by depression induced by work in order to claim an injury award. Aims To quantify the association between depression and subsequent development of type 2 diabetes in order to determine whether an individual in a pension scheme that awards injury pensions, who develops type 2 diabetes, should be awarded an injury pension, if the development of the diabetes followed a work-related depressive episode. Methods Electronic and hand literature searches up to December 2006. Relative risk estimates from cohort studies of adults were pooled using fixed and random effects models. Attributable risk fraction was calculated using the Levin formula. Results The presence of depression or depressive symptoms was associated with increased risk of subsequently developing type 2 diabetes. The pooled fully adjusted relative risk estimate from the three highest quality studies was 1.25 (95% CI: 1.02-1.48) and was homogenous. However, depression was no more frequent among those with and without prevalent, but previously undiagnosed, type 2 diabetes. Conclusion Depression is associated with subsequent development of type 2 diabetes. However, the relative risk estimate is small and only 20% of cases of diabetes can be attributed to depression in people with both conditions. Further research is needed to determine possible causal mechanisms for the association and to ascertain whether depression and diabetes may have a common aetiology.