Christine Albert, M.D., M.P.H., from Brigham and Women's Hospital, Boston, presented the findings of the study today at a JAMA media briefing on women's health in New York.
Regular exercise has several cardiovascular benefits and 30 minutes or more of moderate-intensity exercise almost every day is recommended for healthy adults. Despite the known benefits of exercise, studies have also documented associations between incidents of exertion and sudden cardiac death. Although such deaths are relatively rare, they usually occur unexpectedly among people who appear quite healthy.
Dr. Albert and colleagues used data from the Nurses' Health Study to determine the risk of sudden cardiac death in women during moderate to vigorous exertion. The Nurses' Health Study began in 1976 when 121,701 female registered nurses, aged 30 to 55 years, completed questionnaires about their coronary heart disease (CHD) risk factors, lifestyle and medical history. The women have been followed up every two years, for up to 28 years. For this analysis, 84,888 women provided information on their amount of moderate to vigorous exercise per week in 1980, 1992, 1996, 1998 and 2000.
There were 288 cases of sudden cardiac death among the 84,888 women who completed the 1980 questionnaire. The researchers found that only nine of these deaths actually took place during moderate to vigorous exertion, and that only three of these happened while the women were exercising. Of 69,693 women without a history of CHD, stroke or cancer at the study's beginning, 32 percent (22,172) reported no regular moderate to vigorous exercise and 15 percent (10,680) reported exercising for four or more hours per week.
The absolute risk of sudden cardiac death associated with moderate to vigorous exertion was "exceedingly low," the researchers found, at 1 per 36.5 million hours of exertion. Risk of sudden cardiac death was temporarily elevated during moderate to vigorous exertion, compared with the risk during lesser or no exertion. Regular moderate to vigorous activity lessened this temporary risk, and was also associated with a lower long-term risk of sudden cardiac death.
"Although our data are consistent with prior analyses in men that suggest that physical exertion may trigger sudden cardiac death and that habitual exercise diminished this risk, the magnitude of the risk is much lower in this cohort of women compared with a similar cohort of men," the authors write. "In summary, sudden cardiac death during exertion is an extremely rare event in women, and exercising regularly can significantly minimize risk. Therefore, these data should provide reassurance that moderate to vigorous levels of exercise can be prescribed in a safe fashion to women, and if performed regularly, exercise may even lower long-term risk of sudden cardiac death," they conclude.
(JAMA. 2006; 295: 1399 – 1403. Available pre-embargo to the media at www.jamamedia.org.)
Editor's Note: This work was supported by grants from the National Institutes of Health.
Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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