Chronic stress may reduce the activity of cancer-fighting natural killer (NK) cells in the immune systems of those already predisposed to cancer, according to a new study.
Among people who cared for spouses with Alzheimer's disease, those with a cancer history and high perceived stress had lower levels of NK cell activity than did similar caregivers who did not have cancer. They also had lower levels of NK cell activity than a group whose spouses did not have Alzheimer's, according to Peter P. Vitaliano, PhD, of the University of Washington, Seattle, and colleagues writing in the current issue of Annals of Behavioral Medicine (Vol. 20, No. 3).
Caring for a demented loved one may not in general reduce the body's ability to fight cancer, but it may do so in individuals who specifically perceive themselves as highly stressed and who have a biological predisposition, such as a cancer history, the investigators suggest.
The researchers examined NK activity levels, daily "hassles" and "uplifts," and mood in 80 persons caring for a husband or wife with Alzheimer's disease and 85 who were not caring for a demented spouse. About one quarter of the entire sample had a history of cancer. Spouses were tested initially and again 15 to 18 months later.
NK cell activity was lowest among caregivers with a cancer history who reported a high level of daily hassles, but few daily uplifts, the researchers report. The results held even after they controlled for factors known to influence NK cell activity, including alcohol intake, estrogen replacement therapy, and exercise. Interestingly, depressed mood was not related to NK cell activity at any time during the study.
"Caregivers with cancer histories and high perceived stress initially continued to maintain low levels of NK activity at follow-up," the investigators write. "One might predict that these individuals would have a greater frequency of cancer relapses relative to other older adults."
Annals of Behavioral Medicine is the official peer-reviewed publication of The Society of Behavioral Medicine. For information about the journal, contact editor Arthur Stone, PhD, 516-632-8833.