Patients with depression have an increased risk of developing type 2 diabetes and patients with type-2 diabetes have an increased risk for depression, according to an article in the June 18 issue of the Journal of the American Medical Association.

Sherita Hill Golden, MD, MHS, and her colleagues at Johns Hopkins University analyzed data generated by the Multi-Ethnic Study of Atherosclerosis (MESA), which examined risk factors for atherosclerosis in an ethnically diverse group of 6,814 men and women between ages 45 and 84 years.

During MESA, participants made three visits to clinics over the course of three years to be examined for various atherosclerosis risk factors, including type-2 diabetes and symptoms of depression. The study also collected information on factors such as body mass index, blood pressure, diet and exercise patterns, and smoking habits, as well as information correlated with health in general, such as income and socioeconomic factors.

In the current analysis, the researchers excluded all participants who had high fasting glucose levels at baseline. They then examined whether participants who had elevated symptoms of depression per their baseline questionnaire were more likely than to develop high fasting glucose levels by the end of the three-year study period.

Analysis showed that participants with elevated depressive symptoms at baseline were 42 percent more likely overall to develop diabetes by the end of the study than those without these symptoms. Moreover, the stronger the symptoms, the higher the risk of diabetes, a "dose response" that lends strength to the findings.

Even after adjustment for such factors as overweight, lack of exercise, and smoking, the risk of developing diabetes was 34 percent higher for patients with depressive symptoms.

To investigate whether diabetes could lead to depression, Golden and her colleagues used the same data pool and excluded participants who had elevated depressive symptoms at their initial clinic visit. Then, they examined whether those who had high fasting glucose-with or without a formal diagnosis of diabetes-were more likely to develop depressive symptoms by the end of the study.

The researchers found that patients treated for diabetes, about 9 percent of the group, were roughly 54 percent more likely to develop elevated depressive symptoms than those without diabetes.

Surprisingly, people with prediabetes or untreated diabetes were about 25 percent less likely to develop elevated depressive symptoms than people with normal fasting glucose, a finding Golden's team cannot explain at this time.

Golden, an associate professor of medicine and epidemiology at the Johns Hopkins University School of Medicine, speculates that depression may lead patients to develop behaviors that trigger diabetes or make it worse, such as overeating, not exercising or smoking. Similarly, keeping up with the often extensive treatment regimens to care for their diabetes may make patients' depression worse. Understanding how one condition might lead to another could improve treatments for both problems, she says.

"Having both diabetes and depression can make it difficult for patients to get the good clinical outcomes that we like to see for each of these conditions," says Golden. "To make sure that patients with diabetes and depression receive the best care, we wanted to get to the bottom of the connection between these two conditions.

"It's important that doctors be attuned to look for both conditions in patients at risk for either diabetes or depression," Golden adds. "We may want to develop interventions for both treatments, instead of just one or the other."