Compared with the general population, depressed people tend to smoke more, to overeat, to exercise less and to be overweight. All of these factors increase the risk of diabetes. Golden's study found that these activities contributed to the higher rates of diabetes for subjects with depression.
But there are other factors, too. Golden, an endocrinologist, suspects that depression might cause physiological changes that predispose people to diabetes. Depression raises levels of stress hormones such as cortisol as well as other molecules that lead to inflammation; these chemicals in turn contribute to diabetes.
Depression plays a role in several chronic physical conditions besides diabetes. For years, scientists have known that depression is associated with higher rates of heart disease, stroke, osteoporosis and perhaps dementia. Stress hormones and inflammatory molecules play a role in all of those diseases.
Interestingly, the link between depression and diabetes seems to be closely related to socioeconomic status. A new study by the University of Michigan's Mezuk in the American Journal of Public Health found that people with depression whose level of educational achievement was limited to high school or less had a 200 percent increased risk of becoming diabetic.
But depressed people with at least some college education had no increased risk. Mezuk suspects that the difference has something to do with the fact that in people with less education and income, depression tends to last much longer - probably because this group has less access to treatment. The longer the illness persists, the more chance it has to do harm.
Most researchers think that for diabetic patients who become depressed, worry and anxiety play a central role. The disease is chronic, and patients must think constantly about diet as well as the possibility of complications, which can include heart disease, peripheral nerve problems and blindness.
"Either you have them or you're worried about getting them," said epidemiologist William Eaton. A professor at the Johns Hopkins Bloomberg School of Public Health, he has studied diabetes and depression for years but did not work on the study.
Golden found that diabetic patients getting treatment were more likely to be depressed than patients not in treatment. She suspects that diabetes treatment, which involves regular monitoring and injections, causes psychological stress on patients, thus increasing the risk of depression.
Awareness of the link between the illnesses can make a significant difference: A study last year by University of Pennsylvania researchers found that depressed diabetic patients who received mental health care were half as likely to die after two years compared with depressed diabetic patients who did not receive the extra care.
"Treating depression is not only important for mental health, it's important for physical illness as well," said University of Pennsylvania family medicine specialist Dr. Hillary Bogner, the study's lead author.
david.kohn@baltsun.com
