Leisure-Time Physical Activity and the Risk of Nonfatal Myocardial Infarction in Postmenopausal Women

BACKGROUND: Few studies have examined the association of physical activity with coronary heart disease among women. OBJECTIVE: To examine whether participation in physical activity during leisure time decreases the risk of myocardial infarction in postmenopausal women. METHOD: A population-based, case-control study among enrollees of the Group Health Cooperative of Puget Sound, a health maintenance organization based in Seattle, Wash. Cases were postmenopausal women who sustained an incident nonfatal myocardial infarction during the period 1986 through 1991. Controls were a random sample of Group Health Cooperative enrollees who were frequency matched to the cases by age and calendar year. Participation in physical activity during leisure time was assessed from a telephone interview. A total of 268 cases and 925 controls were interviewed. RESULTS: After adjustment for potential confounding factors, the odds ratios for nonfatal myocardial infarction for women in the second, third, and fourth quartile of total energy expenditure, relative to women in the first quartile, were 0.52 (95% confidence interval, 0.34 to 0.80), 0.40 (95% confidence interval, 0.26 to 0.63), and 0.40 (95% confidence interval, 0.25 to 0.63), respectively. Similar odds ratios were associated with the energy expended in nonstrenuous leisure-time physical activity, and with walking for exercise. CONCLUSION: This case-control study suggests that the risk of myocardial infarction among postmenopausal women is decreased by 50% with modest leisure-time energy expenditures, equivalent to 30 to 45 minutes of walking for exercise three times a week.