For the first time in a single study, Johns Hopkins scientists have found that diabetes contributes to depression and vice versa, confirming long-held assumptions about the intertwined nature of two diseases that affect millions of Americans.
The research, published yesterday in the Journal of the American Medical Association, provides added proof that diabetes plays a role in depression and depression plays a role in diabetes. Previous studies have looked at only one aspect of the link.
For years, researchers had assumed that diabetes led to depression, said University of Michigan epidemiologist Briana Mezuk. The new research provides evidence. "That's what makes this study so great," said Mezuk, an expert on diabetes and depression.
Both ailments affect a significant number of people. Almost 21 million Americans - 7 percent of the population - have diabetes. In Baltimore, the proportion is even higher: One in 10 adults is diabetic, according to the federal Centers for Disease Control and Prevention.
And 30 million adults - about 16 percent of the population - have had at least one bout with serious depression during their lifetime.
"We were able to show that there's a bidirectional association," said the study's lead author, Dr. Sherita Hill Golden, a diabetes expert at the Johns Hopkins School of Medicine.
Golden said she hopes that the study will lead to increased understanding among both doctors and patients that the two illnesses are so closely intertwined. She emphasized in particular that doctors who treat diabetes should watch their patients for signs of depression.
The study looked at an ethnically diverse group of 6,814 men and women between the ages of 45 and 84, spread across the country. Over three years, subjects visited a clinic three times to be examined for symptoms of type 2 diabetes and depression. Type 2 diabetes is a chronic illness in which the body cannot properly remove sugar from the blood. The illness has a genetic component but usually occurs in overweight people or those who eat a high-sugar diet. It differs from type 1 diabetes, which is much less common and is an autoimmune disorder in which the body attacks its own pancreas. The pancreas makes insulin, the hormone that controls blood sugar.
Those with higher levels of depression were almost 50 percent more likely to develop diabetes than those who were not depressed. Subjects who were most depressed were most likely to become diabetic.
