In a large group of Medicare beneficiaries with diabetes, depression was associated with a higher death rate from all causes during a two-year study period. The findings are published in the October 2008 Journal of General Internal Medicine.
Lead author Dr. Wayne Katon, professor of psychiatry and behavioral sciences at the University of Washington (UW), noted that previous research indicates that depression and diabetes is a potentially lethal mix among young to middle-aged patients. Depression also puts patients at greater risk of complications from their diabetes. This more recent study suggests that depression is also a risk factor for mortality in older patients with diabetes. Most Medicare beneficiaries, like the ones in this study, are over age 65. The mean age of the participants was 75.6 years.
The study tracked 10,704 Medicare beneficiaries with diabetes who were enrolled in a disease management program in Florida. They were surveyed at the start of the study with a health assessment questionnaire. Evidence of depression among members of the group came from physician diagnosis, patient reports of having a prescription for an antidepressant in the year before the survey, or patient answers to a brief screening test. For the next two years, the research team recorded the death and cause of death of participants through bi-monthly checks of Medicare claims and eligibility files, or from phone calls with the participants' families.
The research team found that patients with both diabetes and depression had an increased risk of about 36 percent to 38 percent of dying from any cause during the two-year follow-up. Participants with a physician diagnosis of depression were significantly younger than their cohorts, more likely to be female, had more severe medical illness, were less likely to be African-American, and more likely to be Hispanic. These variables were controlled for in the analysis of increased risk. A total of 12.1 percent of participants who had both disorders died during that period. Among those without depression, 10.4 percent died.
Participants who had been treated with one or more antidepressant medications in the year before the study had a 24 percent increased risk of mortality, compared to non-depressed participants. According to the study authors, those patients may have been treated with antidepressants because their depressive symptoms were more severe and persistent than those of more mildly depressed patients who weren't prescribed antidepressants.
There was no difference in the rate of cardiovascular or cerebrovascular events between those treated with antidepressants and those who had no indication of depression.
"Rates of mortality from vascular disease may be decreasing in recent years among patients with diabetes due to more aggressive treatment of high blood pressure, cholesterol, and glucose levels," the researchers surmised, "as well as widespread use of preventative medications such as aspirin and beta blockers."
According to the authors, there may be several reasons why depression worsens chronic diseases such as diabetes. Depression has been associated with inadequate self-care and harmful habits like smoking or overeating. Depression is also associated with nervous system and endocrine system problems, and with inflammatory markers.
The authors noted their study's limitations: the participants were from one geographic region of the United States, and the follow-up period was relatively short. Defining depression in part by physician diagnosis and treatment, they added, may have selected for participants with more severe illness. The study was also not able to obtain information on education, income, weight, smoking habits, physical activity, or compliance in taking medication.
In addition to Katon, the researchers included Drs. Ming-Yu Fan and Jurgen Unutzer from the UW, Dr. Jennifer Taylor from Green River Health in Tampa, Fl.; Dr. Harold Pincus from Columbia University and the Rand Corporation; and Michael Schoenbaum from the National Institutes of Health (NIH) in Bethesda, Md.
Grants from the National Institute of Mental Health of the NIH funded the study.