Even a low level of depressive symptoms in older people can disturb immune system function such that an increased and prolonged inflammatory response follows antigen challenge, according to an article in the October issue of the Archives of General Psychiatry.

“A key conclusion from this study is that a person’s mental health really does matter,” explained Janice Kiecolt-Glaser, MD, senior author of the study. “From this work, we get a clear picture of how the body responds differently depending on whether a person is even mildly depressed or not.”

The researchers evaluated 47 older people who were either current or former caregivers of spouses with progressive dementia and 72 controls (mean age, 71 years) immediately prior to annual influenza virus vaccination and 2 weeks afterward; participants had blood drawn at both time points and were given the short form of the Beck Depression Inventory. The American researchers had predicted there would be a link between a person’s depressive status and the levels of Interleukin-6 found in the blood before and after vaccine challenge.

The survey showed that present and former caregivers had modest levels of depressive symptoms at baseline. Kiecolt-Glaser said “These people are not clinically depressed. On the other hand, clearly things are not right with their world. Caregivers felt ‘blue’ and probably were suffering from some kind of sleep disturbance. They also reported having less energy than normal. All these symptoms had been there for some time.”

When the blood samples were analyzed, the depressed caregivers’ levels of the proinflammatory cytokine Interleukin-6 were 30 percent higher 2 weeks after the influenza vaccination whereas the non-depressed participants’ blood levels were essentially unchanged, Ronald Glaser, PhD, lead study author, said.

“The absence of an overall increase in Interleukin-6 from baseline to after vaccination in the control group is consistent with what we would have expected,” Glaser said. “Generally speaking, there is very little inflammatory response - including the production of Interleukin-6 - in people who have already been exposed to the virus for which they are being vaccinated.

“Because these were older people, most of them already had been exposed to influenza virus. Therefore, the significant increase in Interleukin-6 that we found in the caregivers after vaccination is unexpected and important, primarily because it suggests that even low levels of depression are associated with an increased [Interleukin-6] response to an antigen,” Glaser added.

Sustained higher-than-normal levels of Interleukin-6 have been linked to long-term inflammation which, in turn, is implicated in a host of age-related illnesses including cardiovascular disease, osteoporosis, arthritis, type-2 diabetes, certain lymphoproliferative diseases and cancers, Alzheimer’s disease and periodontal disease, the researchers said, which may make intervention in older patients with even mild levels of depressive symptoms all the more important.