Although epidemiologic studies to date have consistently shown a cardiovascular benefit to regular exercise, the specific level of exertion needed to obtain this effect remains unclear. Manson and associates reported on a large, prospective study that correlated physical activity levels with future risk of cardiovascular events in postmenopausal women.

As part of the Women's Health Initiative Observational Study, a questionnaire on activity levels was completed by 73,743 post-menopausal women 50 to 79 years of age who were ambulatory and had no history of cardiovascular disease or cancer at baseline. Compared with previous population-based trials, this study included larger numbers of participants from minority groups (16.5 percent). The questionnaire assessed average activity level per week and number of hours spent in sedentary activities (i.e., sitting, lying down, sleeping). Participants were followed prospectively for cardiovascular events (new onset of angina, coronary revascularization, myocardial infarction, death from cardiac cause, carotid revascularization, congestive heart failure, stroke) over a period of up to 5.9 years (mean: 3.2 years).

A total of 1,554 new cardiovascular events occurred in this group. There was an inverse relationship between self-reported physical activity level and the risk of new coronary heart disease. When the participants were split into five groups according to increasing level of activity, the relative risk of cardiovascular events progressively declined. After controlling for age, smoking, obesity, socioeconomic status, and several other lifestyle and dietary variables, Manson and colleagues found that the relative risks of cardiovascular events for the quintiles were 1.00, 0.89, 0.81, 0.78, and 0.72. This trend was consistent in post-menopausal women of all ages, white and black women, and obese and nonobese women.

When the analysis split out walking versus vigorous activity, the reductions in cardiovascular events were similar. Walking or vigorous activity for at least 2.5 hours per week produced a risk reduction of about 30 percent. The authors did note that the women with the highest levels of walking and vigorous exercise had the greatest risk reduction (63 percent). A faster pace of walking (2 mph or faster) was associated with a greater reduction in risk. Women who reported spending more hours per day in sedentary activities had an elevated risk of cardiovascular disease compared with the more active women.

The authors conclude that walking and vigorous exercise are prospectively correlated with reductions in the risk of new cardiovascular disease in postmenopausal women.