What's behind the link between type 2 diabetes and depression?

WEDNESDAY June 18, 2008 (foodconsumer.org) -- Diabetes 2 may increase risk of depression, and depression may raise odds of developing diabetes 2, according to researchers from Johns Hopkins University.

Sherita Hill Golden, M.D., M.H.S., and her colleagues reported in the June 18 Journal of the American Medical Association that patients with depression had an increased risk of diabetes and diabetics who received medications for treatment had an elevated risk of depression.

Type 2 diabetes and depression often come together, and doctors have been puzzled by this chicken-and-egg problem for years without knowing what causes what.

Golden and colleagues looked at data for 6,814 men and women (including white, black, Hispanic and Chinese) ages 45 to 85 who participated in the Multi-Ethnic Study of Atherosclerosis for three years to see the relationship between diabetes and depression.

During the three-year follow-up, participants visited three clinics to be examined for various risk factors including type-2 diabetes and symptoms of depression, which could serve as a precursor for full-blown clinical depression.

Other risk factors collected also included body-mass indices, blood pressure, diet and exercise patterns, and smoking habits, as well as information correlated with health in general, such as income and socioeconomic factors.

The first part of the study was meant to determine if depression would have the effect of developing diabetes. For that purpose, the researchers excluded the participants who had high fasting glucose when entering the study and only examined those who were experiencing depression at the beginning of the study.

Results showed that those with elevated depressive symptoms were 42 percent more likely to be diagnosed with diabetes by the end of the study than those without symptoms. And strong symptoms were linked to high risk of diabetes.

The risk of diabetes being diagnosed was still 34 percent higher for patients with depressive symptoms even after other factors such as overweight, lack of exercise, and smoking were considered.

For the second part of the study, Golden and team excluded those who had depression and compared only those who had high fasting glucose with or without a formal diagnosis of diabetes at the time the study began to investigate whether diabetes could lead to depression.

Diabetics who were being treated for their condition (about 9 percent of the group), were about 54 percent more likely to acquire depressive symptoms than those without diabetes, the researchers found.

However, those with pre-diabetes (who are often not treated) or untreated diabetes were 25 percent less likely to have elevated depressive symptoms than those with normal fasting glucose, an observation that the researchers did not know how to explain.

Golden speculated that depression may lead to behavioral changes that trigger diabetes or make it worse, such as overeating, not exercising, or smoking. 

Also she suggested that the often extensive treatment regimens used to treat diabetes may make patients' depression worse.

A health observer affiliated with foodconsumer.org, who was not part of the research team, agreed that diabetes drugs could raise risk of depression and also suggested that depression drugs may boost the odds of diabetes. 

"Depression is a common mental disorder that presents with depressed mood, loss of interest or pleasure, feelings of guilt or low self-worth, disturbed sleep or appetite, low energy, and poor concentration," the World Health Organization states.

The depressive feeling is complex and not easy to classify. When diabetics receive treatment, one likely side effect is hypoglycemia, which among other things makes patients feel bad. Another common side effect is weight gain. Could these be at least part of the reason why treated diabetes patients were more likely to be diagnosed with depression?

On the other hand, certain depression medications are known to induce pancreas problems. Could this and other unknown side effects of these medicines increase the risk of diabetes?

In addition, it is possible that both diabetes and depression share some primary cause such as diet, lifestyle, and/or environmental factors.

By David Liu, Ph.D., and edited by Heather Kelley.
Jun 18, 2008 - 12:23:53 PM