COLUMBUS, Ohio – Researchers here have found a critical chemical pathway through which the human immune system is weakened by chronic stress. The study reinforces earlier work that showed long-term caregivers suffer from impaired immunity.
The new discovery is important because it points to a specific cytokine – Interleukin-6 – as the mechanism by which the immune system may be compromised. An increase in IL-6 has been associated previously with an increased risk for a host of serious diseases in the elderly.
Surprisingly, this new study shows that the immune disregulation marked by the increase in IL-6 can linger in caregivers for as long as three years, even after they had ceased that role.
This suggests that people who care for the chronically ill are themselves at a much greater risk for developing their own serious health problems.
The study was led by Janice Kiecolt-Glaser, a professor of psychology and psychiatry, and Ronald Glaser, a professor of molecular virology, immunology and medical genetics, at Ohio State University and the Institute for Behavioral Medicine Research. The study appears in this week's issue of the Proceedings of the National Academy of Sciences.
The project is the latest part of a long-term study of the health of spouses and others who care for patients with dementia and Alzheimer's disease.
The researchers monitored the health of 117 caregivers of chronic patients and compared them to a control group of 106 others who had no care-giving role. The controls were matched for age, general health and socioeconomic status.
Each of the study participants completed a series of psychological surveys to gauge their perceived levels of stress, depression and loneliness. Additionally, blood samples were drawn from the participants when they entered the study and at least twice annually thereafter.
At the start of this phase of the longitudinal 'caregivers' study, nearly a quarter of the caregivers' spouses had already died. During the six years of the study, an additional 50 spouses died. The monitoring of caregiver health continued even after the death of the spouse.
From the blood samples taken from the participants, the researchers were able to plot IL-6 levels throughout the study. Increased levels of IL-6 are known to be associated with many diseases of the elderly including heart disease, arthritis, osteoporosis, type-2 diabetes and certain cancers.
"We found that the caregivers' average rate of increase in IL-6 was about four times larger than that of the control group," explained Kiecolt-Glaser, "which could have important implications for morbidity and mortality.
"This is key evidence for one pathway through which chronic stress may pose potent health consequences in older people. It may well accelerate the risk of a host of age-related diseases as well as deaths," she said.
Her colleague Ronald Glaser described the continued immune impairment as startling.
"The rate of IL-6 increase among former caregivers continued even several years after their ill spouse had died. The absence of any notable improvement even after they were freed from their caregiving duties may be linked to both biological and psychological mechanisms," he said.
"Stress and depression can permanently alter the responsiveness of the immune system."
The researchers were surprised, they said, that the caregivers' immune status did not "rebound" after a period of bereavement, as earlier studies had seemed to suggest it would.
"The changes in caregivers are not simply an artifact of bereavement," Kiecolt-Glaser said.
The study also provided some preliminary data showing that African-American participants had higher levels of IL-6 than did non-African Americans.
William B. Malarkey, professor of internal medicine; Kristopher J. Preacher, a doctoral student in psychology; Cathie Atkinson, a research psychologist in psychiatry, all at Ohio State University; and Robert C. MacCallum, professor of psychology at the University of North Carolina, were part of the study team.
Earlier work by this research group showed that a person's stress levels can have a detrimental effect on how well certain vaccines immunize, that high stress levels can markedly slow wound healing, and that even short-term stressful events such as arguments and test-taking can weaken a person's immune status.
Support for the research came from the National Institutes of Health, the National Institute of General Clinical Research, National Institute of Mental Health, National Institute on Aging and the National Cancer Institute.
Materials provided by Ohio State University. Note: Content may be edited for style and length.
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