Scientists find new link between depression and inflammation

The findings may open up new treatment avenues for patients suffering from inflammatory disorders and depression.

Because an overactive inflammatory response may contribute to a number of medical disorders as well as to depression, the findings suggest that increased inflammatory responses to stress in depressed patients may be a link between depression and other diseases, including heart disease, as well as contributing to depression itself.

Results of the study, led by Dr Andrew Miller, and Dr Christine Heim, of Emory’s Department of Psychiatry and Behavioral Sciences, are published in the American Journal of Psychiatry.

“Several examples of increased resting inflammation in depressed patients already exist in the literature, but this is the first time anyone has shown evidence to suggest that the inflammatory response to stress may be greater in depressed people,” says Dr Miller.

The study included 28 medically healthy male participants, half of whom were diagnosed with major depression and half of whom were not depressed. The participants were exposed to two moderately stressful situations during a 20-minute time period.

Blood was collected every 15 minutes starting immediately before and then up to an hour and a half after the test to check for key indicators of inflammation. The researchers measured levels of a pro-inflammatory cytokine (a regulatory protein secreted by the immune system) called interleukin-6, and the activity of a pro-inflammatory signaling molecule in white blood cells called nuclear factor-kB.

While at rest (before the stress challenge), the depressed patients had increased inflammation relative to the control group. Both the depressed and the healthy groups showed an inflammatory response to the stress challenge, but people who were currently depressed exhibited the greatest increases of interleukin-6 and nuclear factor-kB.

“While inflammation is essential for us to fight bacterial and viral infections, too much inflammation can cause harm,” says Dr Miller. “There’s always some collateral damage when the immune system gets fired up, and we now believe that too much inflammation, either at rest or during stress, may predispose people to become depressed or stay depressed.”

In addition, medical research over the last decade has shown that runaway inflammation may play a role in a number of disorders, including heart disease, cancer, and diabetes, all of which have been associated with depression.