Stress May Increase Susceptibility To Infectious Disease

Dozens of studies have shown that stress can alter the levels of certain biochemical markers in the body -- key players in the human immune response -- but scientists weren't sure those changes actually led to poorer health.

Now, they seem convinced.

Reporting in the Journal of the American Medical Association, a team of researchers from five universities argue that stress can lessen a person's immune response and that change can make them more susceptible to infectious diseases.

They also say that increased stress may lessen the effectiveness of certain vaccines and can confound some studies of certain illnesses that affect the immune system, such as AIDS and autoimmune diseases.

"The evidence so far suggests that while the immune changes associated with psychological stress are generally small, they look like they're important enough to have biological consequences and increase health risks," explained Ronald Glaser, professor of medical microbiology and immunology at Ohio State University and lead author of the study.

The JAMA paper points to the important role that compounds known as cytokines play in regulating the immune response. In some cases, they stimulate the release of other compounds essential for inflammation. In other cases, they maintain the balance of other components of the human immune response.

Researchers know that psychological stress can alter the level of certain hormones. These alterations induced by stress are responsible for the changes in cytokine concentrations since stress hormones alter the synthesis and the release of the cytokines, the authors explained.

Glaser suggests that while in vitro tissue cultures have taught us much about the immune response, that system may function differently in the whole animal, or person.

The researchers pointed to recent research involving vaccinations for Hepatitis B and for influenza. They showed that stress could suppress T-cell responses and lower antibody levels, two factors necessary to develop a strong immunity to these diseases.

"These vaccination results are particularly relevant to older adults," they wrote. "Our inference is that a poor immunological response to vaccination has medical consequences." Other research showed a relationship between a person's level of psychological stress and their susceptibility to several cold viruses.

The researchers said that AIDS, however, presents unique obstacles for the study of the effect of stress on diseases. In most cases, the pathogen responsible for an infectious disease attacks certain cells within the body and the immune system is activated to fight it.

But with AIDS, the HIV virus attacks those same immune cells that would be called on to fight disease. Glaser said that the approaches now in use to fight HIV infection actually complicates the understanding of the physiological effect that stress has on AIDS patients.

The study team suggested that future research should explore whether improving the concentration of certain hormones in the blood might produce an improvement in immune function.

They also said that enough is known now to show that certain changes in lifestyle can increase a person's resistance to some infectious diseases. Most of these changes -- gaining social support and companionship, maintaining a proper diet, regular exercise and enough sleep -- are not expensive, Glaser said.

At the same time, clinicians need to remember that when a patient fails to live up to the strong lifestyle change suggestions made by their doctor, they may develop guilt feelings about that failure, he said.

The researchers said doctors should focus more on the role stress plays in infections and diseases such as asthma, rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, psoriasis and cancer.

Along with Glaser at Ohio State Medical Center, Bruce Rabin, University of Pittsburgh Medical Center; Margaret Chesney, University of California; Sheldon Cohen, Carnegie-Mellon University; and Benjamin Natelson, the University of Medicine and Dentistry of New Jersey, took part in the study.