By Day Greenberg The Daily Northwestern

Depression is a possible cause of diabetes in older adults, independent of factors such as obesity and inactive lifestyles, according to a study by Northwestern researcher Mercedes Carnethon.

The decade-long study, published April 23 in the Archives of Internal Medicine, found the rate of constant or increasing depression is higher among those who have type 2 diabetes than those who are diabetes-free.

Carnethon, a professor of preventive medicine at NU’s Feinberg School of Medicine, studied nearly 4,700 men and women at least 65 years old, randomly selected from four states. Scientists at the University of Washington in Seattle and Emory and Wake Forest universities helped to collect information on the patients from 1989 to 1999.

The study was part of a larger one focused on cardiovascular health supported by the National Heart, Lung and Blood Institute and the National Institute of Neurological Disorders and Stroke. It tracked self-reported depressive symptoms and other health and lifestyle information to determine if stress and depression could cause type 2 diabetes among the elderly.

Type 2, the most common form of diabetes, is thought to come mainly from an unhealthy, overweight and sedentary lifestyle. According to the American Diabetes Association, type 2 diabetes patients are not receptive to the flowing supply of insulin, the substance that breaks down glucose in the body.

Carnethon said an inactive lifestyle does not offer an all-inclusive reason for developing diabetes, but that it offers only one possible explanation.

“We measured some behavioral factors, and when we took those into account, we still saw that depressive symptoms were still associated with diabetes,” Carnethon said.

The study suggests that a high level of cortisol, a stress hormone, could cause diabetes in people who are depressed by decreasing their sensitivity to insulin and raising glucose levels.

“Depression activates a number of responses in the sympathetic nervous system, the fight-or-flight center, where these hormones are active,” said Feinberg Prof. Philip Greenland. “It has an influence on the metabolism of food and nutrients, and if you interfere with that, it’s not surprising you would get adverse reactions in the body.”

Carnethon said depression, which affects about 20.9 million adults in the U.S., could cause the body to produce less insulin and further reserve glucose in the bloodstream by blocking any insulin that is made.

Other experts said more studies must be conducted before any definitive conclusions can be made about the connection between depression and diabetes.

“If you ask me if this means there is a new medicine for treating diabetes, I would say ‘not yet,'” Greenland said. “But it does suggest a new line of thinking that might have an influence on the future treatment of diabetes.”

There is not a clear way to know for sure whether depression causes diabetes or diabetes causes depression, said David Marrero, an endocrinology professor at Indiana University who helped design the Diabetes Prevention Program for the American Diabetes Association.

“Are you depressed because you have diabetes? More and more evidence leans to depression as a cause of diabetes, but by no means is that conclusive,” he said. “Apparently there are some genetic factors and clearly an association between depression and diabetes, but we don’t have any proof.

“We need more research to really look at which comes first, the chicken or the egg.”

Reach Day Greenberg at [email protected].