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The study, which involved more than 2,500 older people living in or around Pittsburgh and Memphis, Tenn., also found that those with diabetes were at much greater risk of having recurrent depression.
The results were published yesterday in the Archives of Internal Medicine.
Researchers believe the study is the first to investigate whether having diabetes predicts the future onset of significant depressive symptoms, said Dr. Elsa Strotmeyer, a co-author and assistant professor at the University of Pittsburgh's Graduate School of Public Health.
Diabetes and depression are both significant health problems in older Americans. Twelve to 20 percent of older people living in the community report significant depressive symptoms, the study noted.
And diabetes rates tend to be the highest among Americans 65 and older, according to the Centers for Disease Control and Prevention.
The study focused on people 70 to 79 who lived in the community and were in relatively good health. About half lived in the Pittsburgh area, Dr. Strotmeyer said. All were part of the Health, Aging and Body Composition Study, a nine-year effort to investigate the relationships among health conditions, body composition, social and behavioral factors and functional decline.
Participants in the study published yesterday were followed for about six years. People diagnosed with diabetes in childhood and who initially reported depression symptoms or treatment were excluded. The study focused on people with Type 2 diabetes, Dr. Strotmeyer said.
In Type 2 diabetes -- formerly known as adult-onset diabetes -- the body is resistant to the effects of insulin or produces insufficient amounts to maintain normal glucose levels. Left uncontrolled, the disease can cause a number of complications, some of which are life-threatening. The condition is on the rise, fueled in part by an increase in obesity.
In the study published yesterday, about 23 percent of participants had diabetes, and more than one-third were diagnosed with the disease at the start of the study. Dr. Strotmeyer noted that many people with diabetes are unaware they have the disease.
Researchers found that study participants with diabetes had a higher first onset of depressed mood, resulting in treatment for depression or significant depressive symptoms, than people without diabetes. Adjusting for demographic characteristics and other factors, diabetes was associated with a 20 percent increased risk for having an episode of depression, Dr. Strotmeyer said.
Diabetes also was associated with greater risk of persistent depression. Participants with diabetes had a 90 percent increased risk of recurrent depressive mood based on an evaluation at two consecutive annual clinic examinations, she said. People with uncontrolled diabetes were most likely to be affected.
Dr. Strotmeyer said the greater likelihood of depressive symptoms could be linked in part to the emotional burden of dealing with some of the health problems often associated with diabetes, such as obesity, coronary heart disease, kidney disease or physical impairments.
"I think the public health message here is that if you control your diabetes and treat some of the complications, it could potentially reduce depressive mood," Dr. Strotmeyer said.
