A large new study confirms what some others have found—that there is a link between depression and type 2 diabetes. Moreover, it has found an increased incidence of depression even in people who are unaware that they have type 2 diabetes.

The study was headed by Catharine Gale, Ph.D., a principal research fellow in epidemiology at Southampton General Hospital in England. Results were published online November 6, 2009, in Biological Psychiatry.

As part of the Vietnam Experience Study conducted by the U.S. Centers for Disease Control in the 1980s, some 4,300 Vietnam vets had their fasting blood glucose levels measured and were also assessed for major depression. The researchers were evaluating whether there was a link between having type 2 diabetes and major depression.

Gale and her group found that men who were aware that they had type 2 diabetes were almost four times as likely to have major depression as were men who did not have diabetes. But even men who were unaware that they were diabetic were at twice the risk of having major depression as were men who did not have diabetes.

This cross-sectional study does not shed light on how depression and type 2 diabetes are coupled, but there are various hypotheses. For example, if people know that they have type 2 diabetes and feel compelled to cope with it, that knowledge might depress them. Yet because depression was linked with type 2 diabetes even in men who were not aware that they had diabetes, it argues against this explanation, the researchers believe.

In fact, longitudinal studies have suggested that depression may increase the risk of developing type 2 diabetes, Gale told Psychiatric News. If that is the case, then depression might do so by activating hypothalamic-pituitary-adrenal hormones, since activation of these hormones is linked with both depression and development of type 2 diabetes.

Meanwhile, the results from this study have implications for psychiatrists, Gale said. "Our results provide further confirmation that depression and type 2 diabetes commonly co-occur. Doctors caring for people with depression should perhaps be aware that they may be at particular risk of type 2 diabetes."

The study was funded by the United Kingdom Biotechnology Sciences Research Council, Wellcome Trust, and other sources.

An abstract of "Fasting Glucose, Diagnosis of Type 2 Diabetes, and Depression: The Vietnam Experience Study," can be accessed at <http://www.journals.elsevierhealth.com/periodicals/bps> by clicking on "Articles in Press."