Mar. 23, 1999 Scientists have identified what may be an important biological link between stress and the common cold. The culprit: interleukin-6 (IL-6), a chemical pathway used by the immune system.
In a 1991 report in the New England Journal of Medicine, Sheldon Cohen, PhD, of Carnegie Mellon University in Pittsburgh had earlier found a clear link between psychological stress and a propensity to be infected by respiratory viruses.
The new work by Cohen and colleagues (William Doyle, PhD, and David Skoner, MD, of The Children's Hospital of Pittsburgh) finds that the cytokine IL-6 may be a major pathway between mind and body by which stress makes the body more susceptible to developing infection and symptoms of respiratory illness.
"Even with certain reservations, this is the first study to provide evidence consistent with the hypothetical model that psychological stress influences upper respiratory infectious illness through a biological pathway," they report in the March issue of Psychosomatic Medicine.
The finding is a significant step forward in establishing a direct biological link between stress and human illness. Until now, Cohen and his colleagues have been able to establish stress as a risk factor for respiratory illness, but they have only been able to speculate on the potential biological pathway that links stress to greater risks of colds and flu.
For this study, Cohen and his colleagues measured the levels of psychological stress of 55 adult volunteers before infecting them with an influenza A virus and quarantining them for eight days. All participants developed verified infection with the same strain of influenza A virus. At the end of each day, the participants rated the severity of their respiratory symptoms -- sneezing, nasal congestion and discharge, sore throat, cough, malaise, headache, and chilliness. Their mucus production was measured by collecting and weighing used tissues.
Levels of the IL-6 were measured daily in nasal secretions. During the early period of infection, the concentration of IL-6 in each participant's secretions varied with the symptoms and volume of mucus provoked by the infection, suggesting that it may be a common pathway through which upper respiratory virus infection is translated into symptoms.
Also, greater concentrations of IL-6 were found in the secretions of participants who reported greater psychological stress before being infected, suggesting that IL-6 production may also be a biological link between stress and illness severity, the scientists report. "Our analyses suggest that most of the effect of psychological stress on symptoms and mucus weights could be accounted for by changes in IL-6," the researchers say. "However, it is possible that IL-6 itself is not the causal link but rather just a marker…of other unassayed proinflammatory chemicals increased during the course of experimental infection."
The research was supported by grants from the National Institute of Mental Health, from the National Institutes of Health, and the John D. and Catherine T. MacArthur Foundation Network of Socioeconomic Status and Health.
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