Older adults who have symptoms of depression at least one time over a ten-year period may have a higher risk for development of type 2 diabetes than peers without depressive symptoms, according to an article in the April 23 issue of Archives of Internal Medicine.

Previous research has suggested 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 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 wrote.

Mercedes R. Carnethon, PhD, of Feinberg School of Medicine, Northwestern University, Chicago, and colleagues followed 4,681 participants age 65 and older (average age 72.7) who did not have diabetes at baseline in 1989.

Each year for 10 years, 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 0 to 30, with scores of 8 or higher indicating high levels of symptoms.

Sociodemographic characteristics, clinical measures including height and weight, and information about medication use that would indicate development of diabetes were also updated annually.

At baseline, the average depressive symptom score was 4.5, and 20 percent of participants had a score of 8 or higher. During follow-up, scores increased by at least 5 points in nearly half the participants, and 234 individuals developed diabetes. Rates of diabetes were higher among those with a score of 8 or higher compared with those who had scores below 8.

"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 wrote. "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 wrote.

"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 concluded. Because an estimated 2 million older adults experience depression or a related illness and 15.3 percent of those over 65 years 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."