Several other studies presented at the ADA meeting addressed the chicken and egg issue of whether depression causes diabetes or vice versa.

In one such study, researchers from Emory University School of Medicine in Atlanta examined blood sugar control, or glucose tolerance, of 443 healthy adults without known diabetes or glucose intolerance who were and were not being treated for depression. Glucose intolerance is the major indicator of diabetes.

The researchers thought they would find that depressed patients had higher levels of prediabetes and undiagnosed diabetes disease than people who were not depressed, but this is not what they found.

After adjusting for diabetes risk factors such as weight, age, and race, little association was seen between depression and glucose intolerance. Although diabetes was associated with depression, unrecognized glucose intolerance was not.

Since these results suggested that awareness of the health risks conferred by diabetes may contribute to depression, patients with newly diagnosed glucose intolerance should be counseled appropriately and monitored for development of depression, researcher Lawrence S. Phillips, MD, and colleagues wrote.

Role of Hormonal Changes

But other research suggests that depression predisposes people to diabetes. In a presentation at the ADA meeting Johns Hopkins School of Medicine epidemiology professor Sherita Hill Golden, MD, suggested that hormonal changes seen with depression could also cause diabetes.

Specifically, the stress hormones adrenaline and cortisol could be the culprits, she tells WebMD.

"Both of these hormones are increased in people who have depression, and we also know that these two stress hormones also alter glucose metabolism as well," she says.

Stress hormones are also thought to play a role in cardiovascular risk.

If the theory is correct, then medications being developed to keep these hormones in check may prove to be effective diabetes and heart-disease-prevention drugs, she says.