While these factors are important, the new research adds to the evidence that biological as well as lifestyle factors contribute to type 2 diabetes, researcher Julie Wagner, PhD, of the University of Connecticut Health Center, tells WebMD.
Wagner's study was presented Saturday at a meeting of the American Diabetes Association in New Orleans.
"Insulin resistance is the hallmark of type 2 diabetes, and this study shows that treating depression is associated with improved insulin resistance," Wagner tells WebMD.
Depression and Diabetes
Depressed participants who were not being treated had significantly greater insulin resistance than study participants who were not depressed. But treatment for depression appeared to improve insulin sensitivity, with depressed participants on antidepressant therapy having similar insulin sensitivity to non-depressed participants.
"Basically the depressed people on medication looked like the non-depressed people in terms of insulin sensitivity," Wagner says.
Stress Hormones and Belly Fat
The findings support a recently published analysis of more than a dozen studies suggesting that depression is a much stronger risk factor for type 2 diabetes than diabetes is for depression.
There are several theories about how depression may contribute to type 2 diabetes, but the most widely cited theory involves the stress hormone cortisol.
Cortisol is a key player in blood sugar metabolism and insulin sensitivity.
High cortisol levels are also associated with increased fat deposits around the abdomen, or belly fat, which is a risk factor for type 2 diabetes.
In short, the theory suggests, the more depressed someone is, the more cortisol they produce, which leads to more belly fat and more diabetes, says Wagner.
Depression may also influence type 2 diabetes risk by disrupting the immune system or levels of serotonin, which helps modulate metabolic function as well as mood, Wagner says.
Depression and diabetes researcher Patrick Lustman, PhD, tells WebMD that understanding how depression influences diabetes could have major implications for the management of at-risk patients.
Lustman is a professor of psychiatry at Washington University School of Medicine in St. Louis.
"When you think of interventions that target both depression and diabetes, physical activity has to be at the top of the list," he tells WebMD. "Exercise is the most powerful preventive medicine we have for type 2 diabetes, and it is arguably among the most powerful treatment for depression."