The research carried out annually on men and women over 65 in three states was the first to chart a link between diabetes and symptoms of depression over a long period.

"Chronic depression or depression that worsens over time may cause diabetes in older adults," the study's authors at Northwestern University in Chicago said in a statement Monday presenting the findings, which are published in Archives of Internal Medicine.

"This means doctors need to take depressive symptoms in older adults very seriously because of the effect it has on the likelihood of developing diabetes," lead author Mercedes Carnethon, assistant professor of preventive medicine, said in the report.

"Diabetes is a scourge," she added. "It causes heart disease, blindness, kidney disease, leg amputations and lowered cognitive function because it essentially degrades the small and large blood vessels."

An estimated two million "older adults" suffer from clinical depression, while people aged 65 and older also have the highest prevalence of Type 2 diabetes, the report said.

"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 added.

"But even after we adjusted for body mass index (measure of height versus weight), we still saw a residual association between depression and diabetes."

Carnethon suggested that the link may be due to a high level in depressives of the stress hormone cortisol, which can lead to lowered levels of insulin, the hormone that helps process sugar in the blood. Diabetics suffer from insulin deficiency.

Although the study only looked at those over 65, she warned the trend may also affect depressed younger adults.

AFP