STUDY SHOWS LINK BETWEEN DEPRESSION, DIABETES IN OLDER ADULTS

While Type 2 diabetes generally is thought to be a disease of lifestyle, with obesity and inactivity the primary causes, researchers now see a relationship between chronic depression and development of adult-onset diabetes. A recent study suggests for the first time that adults age 65 and older who are chronically depressed are more likely to develop this inability to produce enough insulin to get rid of excess blood sugar.

A study at the Northwestern University Feinberg School of Medicine used information that the National Institutes of Health had gathered annually from more than 4,600 people age 65 and older who were not diabetic at the beginning of the 10-year study. They also answered questions about mood, irritability, energy level, concentration and sleep (for more information, read the press release about this study, which is online at http://www.northwestern.edu/newscenter/stories/2007/04/depression.html.) 

The data showed that, independent of weight and activity levels, the older adults who reported high depressive symptoms were 50 percent more likely to develop diabetes than those who did not. Mercedes Carnethon, an epidemiologist and assistant professor of preventive medicine, said this research implies that depression is important for reasons other than its effects on mood.

This study will be published in April in the Archives of Internal Medicine.

A sample from the study follows:

“An estimated 2 million older adults suffer from clinical depression, the second highest incidence of any age group. People 65 and older also have the highest prevalence of Type 2 diabetes. “Diabetes is a scourge,” said Carnethon. “It causes heart disease, blindness, kidney disease, leg amputations and lowered cognitive function because it essentially degrades the small and large blood vessels.”

The study differed from prior research in several ways. It is the first to examine the connection between increasing symptoms of depression over time and the incidence of diabetes.

Previous studies linking diabetes to depression have been based on a one-time measure of depressive symptoms. A single measure could be based on an episode or event that has caused a person to feel blue for a limited amount of time.

Carnethon’s study measured depressive symptoms at a single point in time as well as depressive symptoms over time.  This approach paints a more accurate depiction of depressive symptoms.  By measuring depressive symptoms before diabetes developed, she and colleagues were better able to investigate the causal effect between mood and diabetes.

The Northwestern study also factored out other known lifestyle causes of diabetes such as being overweight or getting little physical exercise.

“We know that overweight and obesity are the primary risk factors for diabetes and most people with Type 2 diabetes are overweight or obese,” Carnethon said. “But even after we adjusted for [statistically accounted for] body mass index (measure of height versus weight), we still saw a residual association between depression and diabetes.” 

In addition, the study considered a key biological factor – a high level of inflammation common in depressed people – that might have explained the link between depression and diabetes. Inflammation is estimated by the levels of an inflammatory protein in the blood called C-reactive protein. But even after accounting for levels of the protein, depressive symptoms were still associated with the development of diabetes.

Carnethon theorizes that the culprit responsible for diabetes in persons who are depressed is a high level of a stress hormone, cortisol.”