"This is the first demonstration that caregiving can lead to mortality," said the leader of the study, Richard Schulz, a psychiatry professor and director of the University Center for Social & Urban Research at the University of Pittsburgh.
The researchers, whose study is published in Wednesday's Journal of the American Medical Association, spent four years tracking 819 spouses, ages 66 to 95.
A total of 317 were responsible for helping a spouse move around the house, eat or go to the bathroom; or handled the partner's laundry, housework or shopping.
Of those 317 caregivers, 179 reported strain. Those caregivers had higher levels of depression and were less likely than other spouses to get enough exercise and rest or to see a doctor when they were sick.
"My hunch is that these people are frail. They're relatively old. They have their own health problems generally," Schulz said.
Past studies have suggested that loss, prolonged distress, the physical demands of caregiving and the biological vulnerability of older people may lead to health problems in elderly caregivers.
The spouses who needed care suffered from such ailments as arthritis, congestive heart failure, strokes and Alzheimer's disease.
The strained caregivers, like the spouses studied, died of such things as heart disease, stroke, cancer, pneumonia and kidney failure.
Stephen McConnell, vice president for public policy at the Alzheimer's Association, said the study underscores the need to support caregivers. He noted that Medicare covers elderly caregivers if they get sick but does not pay for relief help that could keep them from falling ill.
"It's a short-sighted policy," McConnell said.
In the study, 103 deaths occurred among subjects. That included 40 (9.4 percent) of 427 participants whose spouses were not disabled at the study's outset; 13 (17.3 percent) of 75 subjects who had disabled spouses but were not caregivers; 19 (13.8 percent) of 138 subjects who were providing care and were not strained; and 31 (17.3 percent) of the 179 who were providing care and reported strain from it.
After taking into account factors that could affect the likelihood of dying, researchers estimated that strained caregivers were 63 percent more likely to die within four years than other spouses, caregivers or not.
By Brenda C. Coleman