Levels of a damaging compound known as a proinflammatory cytokine not only increased considerably faster among those taking care of ailing spouses but also continued to increase faster for years after the spouses died.
A report on the research, conducted by scientists at Ohio State University and the University of North Carolina at Chapel Hill, will appear online Monday afternoon (June 30) in the Proceedings of the National Academy of Sciences.
Authors are Drs. Janice K. Kiecolt-Glaser, Cathie Atkinson, William B. Malarkey and Ronald Glaser of Ohio State's College of Medicine and Drs. Robert C. MacCallum and Kristopher J. Preacher of UNC's department of psychology, College of Arts and Sciences.
"Our study examined effects of a long-term chronic stress situation on overproduction of the cytokine IL-6 in older adults," said MacCallum, director of the L.L. Thurstone Psychometric Laboratory at UNC. "IL-6 is a substance secreted by a variety of cells in the body, including blood cells and bone marrow. Among other things, it is associated with the functioning of the immune system in its response to challenges, as well as the inflammatory response to injury and infection."
As people age, production of IL-6 tends to increase, he said. Overproduction of IL-6 has been linked to a variety of age-related conditions, including cardiovascular disease, arthritis, periodontal disease, frailty and diabetes.
The study involved examining IL-6 levels in two groups of older adults over six years. One group of 119 people consisted of men and women who were caring for a spouse with dementia, usually Alzheimer's disease. The other group consisted of 106 people who were not caregivers. When they entered the investigation, subjects' average age was 70.5 years.
"Statistical analyses showed a more rapid increase in IL-6 level for the caregiver group than for the non-caregiver group, such that the average rate of increase was about four times greater in the caregiver group," MacCallum said.
The team carried out additional analyses to learn whether the difference might be associated with other variables such as age, gender, ethnicity, depression, loneliness or health-related behaviors including smoking, exercise and sleep patterns.
"We found no other variables that accounted for the group difference in rate of change in IL-6," MacCallum said.
Before and during the study, some of the spouses of the caregivers died, he said. Further analyses compared levels of the proinflammatory cytokine in former caregivers and those who continued taking care of their loved ones. Results showed no significant difference in rate of change in IL-6 between the two groups, indicating that the negative impact of caregiving may last long after the ill spouse has died.
"Overall, the study provides evidence that a severe chronic stress situation can accelerate production of IL-6, a phenomenon which has been shown to be associated with the onset and course of a variety of age-related diseases and conditions," MacCallum said. "In effect, this phenomenon represents a sort of premature aging of the immune response."
UNC News Services
Note: Kiecolt-Glaser can be reached at 614-292-0033, MacCallum at 919-962-4016.
Proceedings of the National Academy of Sciences