The association of comorbid depression with mortality in patients with type 2 diabetes

OBJECTIVE - We assessed whether patients with comorbid minor and major depression and type 2 diabetes had a higher mortality rate over a 3-year period compared with patients with diabetes alone. RESEARCH DESIGN AND METHODS - in a large health maintenance organization (HMO), 4,154 patients with type 2 diabetes were surveyed and followed for up to 3 years. Patients initially filled out a written questionnaire, and HMO-automated diagnostic, laboratory, and pharmacy data and Washington State mortality data were collected to assess diabetes complications and deaths. Cox proportional hazards regression models were used to calculate adjusted hazard ratios of death for each group compared with the reference group. RESULTS - There were 275 (8.3%) deaths in 3,303 patients without depression compared with 48 (13.6%) deaths in 354 patients with minor depression and 59 (11.9%) deaths among 497 patients with major depression. A proportional hazards model with adjustment for age, sex, race/ethnicity, and educational attainment found that compared with the nondepressed group, minor depression was associated with a 1.67-fold increase in mortality (P = 0.003), and major depression was associated with a 2.30-fold increase (P < 0.0001). In a second model that controlled for multiple potential mediators, both minor and major depression remained significant predictors of mortality. CONCLUSIONS - Among patients with diabetes, both minor and major depression are strongly associated with increased mortality. Further research will be necessary to disentangle causal relationships among depression, behavioral risk factors (adherence to medical regimens), diabetes complications, and mortality.