The women participating in this study were selected from the pool of 13,000 women involved in the National Runners' Health Study. Williams is the principal investigator for the National Runners' Health Study, which also involves 42,000 men. The study of women runners was limited to those who are nonsmokers, who are not taking medications, and who are not vegetarians. Before comparing the distance run by the women to their cholesterol, blood pressure, and body masses, Williams and Moussa adjusted for a number of factors. Women who take estrogen also benefit.
Vigorous exercise appears to beneficially effect cholesterol metabolism.
The findings of this study bring into question the exercise guidelines recommended by the U.S. Center for Disease Control and Prevention and the American College of Sports Medicine. These guidelines advocate moderate exercise, for instance, a brisk two-mile walk every day. Furthermore, current guidelines suggest that there is little additional benefit to be gained from doing anything more. There does not seem to be any diminishing return before running 40 miles per week. With exercise, the greater the investment, the greater the rewards.