Depression linked to development of diabetes in older adults

Older adults who have had symptoms of depression, whether those symptoms occurred once, increased or remained steady over a 10-year period, may be more likely to develop diabetes than those without depressive symptoms, according to a report in the April 23 issue of Archives of Internal Medicine.

Previous research suggests that high levels of symptoms of depression, including irritability and trouble sleeping, are associated with increased risk of development of type 2 diabetes, according to background information in the article. However, with few exceptions, most of the studies have defined symptoms of depression based on a single survey filled out by participants. "Given the episodic nature of depression and depressive symptoms, a single self-report of symptoms may not fully characterize the association between depressive symptoms and diabetes," the authors write.

Mercedes R. Carnethon, Ph.D., of Feinberg School of Medicine, Northwestern University, Chicago, and colleagues followed a group of 4,681 participants age 65 and older (average age 72.7) who did not have diabetes at the beginning of the study in 1989. Each year for 10 years, the participants were evaluated for the presence of 10 symptoms of depression, including those related to mood, irritability, calorie intake, concentration and sleep. Symptoms were scored on a scale of zero to 30, with scores of eight or higher indicating high levels of symptoms. Sociodemographic characteristics, clinical measures including height and weight, and information about medication use that would indicate the development of diabetes were also updated annually.

At the beginning of the study, the average depressive symptom score was 4.5, and one-fifth of participants had a score of eight or higher. During the follow-up period, scores increased by at least five points in nearly half the participants, and 234 individuals developed diabetes. Rates of diabetes were higher among those with a score of eight or higher, compared with those who had scores below eight.

"In this sample of older adults, a single report of high depressive symptoms, an increase in symptoms with time and persistently high symptoms over time are each associated with an excess incidence of diabetes," the authors write. "Furthermore, increasing symptoms with time are associated with incident diabetes beyond initial high depressive symptoms and the association between increasing scores and incident diabetes was strongest among those with initially low baseline scores."

These associations were not explained by considering other risk factors for diabetes, including physical activity, smoking and body mass index. "The pathophysiologic mechanism for this association remains unclear," the authors write.

"Our findings in this population of older adults are of particular public health importance because there are 35 million U.S. adults older than 65 years," they conclude. Because an estimated 2 million older adults experience depression or a related illness and 15.3 percent of those over 65 have diabetes, "findings from this study of a novel and highly prevalent risk factor for diabetes have important implications for a substantial subset of our population."

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