Researchers at the University of Washington (UW) and at Group Health Cooperative, a large, Seattle-based health plan, conducted the study. The researchers surveyed and followed up 4,154 patients with type 2 diabetes. The patients filled out written questionnaires. With patients' consent, automated diagnostic, laboratory, and pharmacy data were collected from the HMO. The researchers also reviewed Washington state mortality data to analyze diabetes complications and deaths.
Depression is common among people who have type 2 diabetes. This high prevalence can have unfortunate repercussions. Both minor and major depression among people with diabetes are strongly linked with increased mortality.
"Depression may be associated with increased mortality in patients with diabetes because of both behavioral and biologic factors," the researchers noted in their article. More work, they added, is needed to untangle the cause-and-effect relationships among depression, behavior, diabetes complications, and mortality.
Dr. Wayne Katon, professor and vice chair of the UW Department of Psychiatry and Behavioral Sciences, led the recent study. He is a noted researcher on the associations between depression, aging, and chronic diseases, and on the medical costs and personal toll from untreated or inadequately treated depression. The research team included Drs. Carolyn Rutter, Greg Simon, Elizabeth Lin, Evette Ludman, and Michael Von Korff from the Group Health Cooperative Center for Health Studies; Dr. Paul Ciechanowski, UW assistant professor of psychiatry and behavioral sciences; Dr. Leslie Kinder from the Veterans Affairs Puget Sound Health Care System; and Dr. Bessie Young from the UW Department of Medicine.
Previous studies by Katon's research group have shown that patients with depression and diabetes are less likely to follow diet and exercise guidelines or to check their blood glucose levels, and to have more lapses in filling their prescriptions for oral hypoglycemic, lipid-lowering, and high blood pressure medications. People with depression and diabetes were also more likely to have three or more heart disease risk factors, such as smoking, obesity, and a sedentary lifestyle, compared to people with diabetes alone.
Patients with both depression and diabetes are also significantly more likely to have cardiovascular and cerebrovascular complications. Depression may increase complications, not only because of poor self-care, but possibly through the brain chemistry and nervous system abnormalities that accompany depression, the researchers noted. They added that people may also become depressed in response to changes in their ability to function or because of physical symptoms, such as chronic pain from nerves damaged by diabetes.
In the UW and Group Health study, patients with diabetes accompanied by minor depression were less educated and were less likely to be Caucasian, in comparison to the diabetes patients without depression. Patients with diabetes and major depression were significantly younger, less likely to be married, and more likely to be female than were diabetes patient without depression. Both those with major and minor depression were more likely to have two or more diabetes complications, and were more likely to have another medical condition in addition to diabetes. They were also more likely to smoke, to be sedentary, to have obesity, and to have been treated with insulin. Compared to diabetes patients with minor depression, those with major depression were more likely to be younger, female, and unemployed.
The researchers pointed out that a sedentary lifestyle was an important, independent predictor of mortality from diabetes. Earlier studies have shown that lack of exercise and physical activity can predict depression, and, conversely, that depression can predict the development of a sedentary lifestyle. Other studies have shown that improvements in treating depression in diabetes patients can lead to the patients exercising more and to better physical functioning.
The findings on diabetes, depression and higher mortality rates are similar to results seen in several studies on heart disease and depression, and may eventually point to important correlations. In people with coronary artery disease, depression is associated with about a two-fold increase in risk of death. Moreover, cardiovascular illness is a leading cause of death among people with diabetes. Some 70 percent to 80 percent of people with diabetes die from coronary artery disease. Among the biological factors that might account for the link between depression and the heightened risk of heart attack or stroke are increases in the ability of platelet cells to clump together inside of blood vessels, an increase in inflammatory markers, and changes in heart rhythms.