Depression and increased mortality in diabetes: unexpected causes of death

Recent evidence suggests that depression is linked to increased mortality among patients with diabetes. This study examines the association of depression with all-cause and cause-specific mortality in diabetes.

We conducted a prospective cohort study of primary care patients with type 2 diabetes at Group Health Cooperative in Washington state. We used the Patient Health Questionnaire (PHQ-9) to assess depression at baseline and reviewed medical records supplemented by the Washington state mortality registry to ascertain the causes of death.

Among a cohort of 4,184 patients, 581 patients died during the follow-up period. Deaths occurred among 428 (12.9%) patients with no depression, among 88 (17.8%) patients with major depression, and among 65 (18.2%) patients with minor depression. Causes of death were grouped as cardiovascular disease, 42.7%; cancer, 26.9%; and deaths that were not due to cardiovascular disease or cancer, 30.5%. Infections, dementia, renal failure, and chronic obstructive pulmonary disease were the most frequent causes in the latter group. Adjusting for demographic characteristics, baseline major depression (relative to no depression) was significantly associated with all-cause mortality (hazard ratio [HR]=2.26, 95% confidence interval [CI], 1.79-2.85), with cardiovascular mortality (HR = 2.00; 95% CI, 1.37-2.94), and with noncardiovascular, noncancer mortality (HR = 3.35; 95% CI, 2.30-4.89). After additional adjustment for baseline clinical characteristics and health habits, major depression was significantly associated only with all-cause mortality (HR = 1.52; 95% CI, 1.19-1.95) and with death not caused by cancer or atherosclerotic cardiovascular disease (HR = 2.15; 95% CI, 1.43-3.24). Minor depression showed similar but nonsignificant associations.

Patients with diabetes and coexisting depression face substantially elevated mortality risks beyond cardiovascular deaths.