About one in seven American women have raised a grandchild for six months or more, but grandmothers who provide care for even a few hours a day may be at increased risk for heart attacks, a new study suggests.

The study by Sunmin Lee, Sc.D., of the Harvard School of Public Health and Harvard Medical School and colleagues found that women who cared for grandchildren at least nine hours a week had a 55 percent increased risk of heart attack.

"In comparison to women not providing child care," Lee says, "providing care to grandchildren nine hours or more per week was associated with a significantly increased risk of coronary heart disease even after control for a number of potential confounders."

The study appears in the November issue of the American Journal of Public Health.

Lee and colleagues gathered data from 54,412 women responding to the Nurses Health Study, a continuing investigation of the health of female registered nurses in the United States begun in 1976. The nurses answer questionnaires every two years about their health status and risk factors.

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The researchers based their study on information from the 1992 Nurses Health Study survey, following the women until 1996. They excluded anyone who had been diagnosed with heart disease, stroke or cancer by 1992. During the next four years, 321 heart attacks occurred among the all nurses. After statistical adjustment for other factors, Lee's team determined that caring for grandchildren more than nine hours a week or for children more than 21 hours a week increased the risk of heart disease.

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Other researchers had suggested previously a "second-shift" hypothesis - that the combined burden of a day's work and the need to care for children afterward produces added stress that may lead to poor health. Also, the well-known Framingham Heart Study found rates of heart disease almost three times higher among working women compared to housewives. Lee's study, however, failed to confirm those findings.

"Analyses by working status demonstrated that women who were not working and provided care to grandchildren had a greater relative risk than women who worked and provided care to grandchildren for the same amount of time," Lee says.

This study was not designed to find the reasons accounting for the association between caring for grandchildren and heart disease. Other studies have shown that caregiving grandmothers were more likely to be classified as depressed, compared to non-caregivers. Lee speculates that these women simply may not have the time to take care of themselves.

"It is possible that women - especially grandmothers - with high levels of child-care demands have less opportunity to engage in their own self-care and in preventive health behaviors," he says.

Center for the Advancement of Health / Health Behavior News Service