All-Cause Mortality Increased in Diabetes Patients with Comorbid Depression

"From incidence to complications and mortality, depression is linked to adverse health effects of diabetes," write Elizabeth Lin, MD, MPH, from the Group Health Research Institute in Seattle, Washington, and colleagues. "Depression-diabetes comorbidity is characterized by younger age of diabetes onset; poor management of diet, exercise, and medications; less favorable glycemic control; and higher risk of complications.... This study examines the association of depression with all-cause and cause-specific mortality in diabetes."

At the Group Health Cooperative in Washington State, the investigators used the Patient Health Questionnaire to evaluate depression at baseline and reviewed medical records supplemented by the Washington State mortality registry to determine the causes of death among 4,184 primary care patients with Type 2 diabetes.

During follow-up, 581 patients died. There were 428 deaths in patients with no depression (12.9%), 88 deaths in patients with major depression (17.8%), and 65 deaths in patients with minor depression (18.2%). Causes of death were cardiovascular in 42.7%, cancer in 26.9%, and other in 30.5% of patients (mostly infections, dementia, renal failure, and chronic obstructive pulmonary disease).

Compared with no depression, major depression at baseline was significantly associated with all-cause mortality (hazard ratio [HR], 2.26; 95% confidence interval [CI], 1.79 -- 2.85); cardiovascular mortality (HR, 2.00; 95% CI, 1.37 -- 2.94); and noncardiovascular, noncancer mortality (HR, 3.35; 95% CI, 2.30 -- 4.89) after adjustment for demographic factors.

After additional adjustment for clinical factors and health habits at baseline, 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). Although similar trends were observed for minor depression, they did not reach statistical significance.

"Patients with diabetes and coexisting depression face substantially elevated mortality risks beyond cardiovascular deaths," the study authors write.

Limitations of this study include evaluation of depression at a single time point, lack of data about the history of depression before baseline measurements, lack of information on medication adherence, and potential for residual confounding.

"The association of depression with a wide spectrum of mortality causes calls for reexamination of the causal mechanisms underlying the link between depression and excess mortality," the study authors conclude. "These factors are likely to be pervasive and to include both physiologic and behavioral pathways.... To decrease the mortality burden for patients with comorbid diabetes and depression, studies should examine interventions aimed at improving health behavior, medication adherence, and better control of medical comorbidities, in addition to optimal depression care."