Current guidelines on physical activity and health may underestimate the benefits of prolonged vigorous exercise in women. That's the conclusion suggested by the results of a study of women runners that is part of the ongoing National Runners' Health Study.
Berkeley Lab life scientist Paul Williams and research assistant Davina Moussa, who conducted the study, are presenting their findings at the 68th Scientific Sessions of the American Heart Association that is taking place November 13-16 in Anaheim, California.
The study, which involved 1,833 women, examined the issue of how much exercise is beneficial. Confirming that exercise improves health, the findings challenge the notion that modest amounts of moderate exercise provide benefits that are almost equivalent to that from extensive, vigorous activity.
Among women runners, vigorous exercise paid off in a range of significant health benefits. A more heart-healthy cholesterol profile was obtained. Weight was significantly reduced, particularly around the waist and hips. And modest improvements were observed in blood pressure.
Importantly, the study found that the more miles a woman runs, the greater were these benefits. That was true up to 40 miles per week.
Williams and Moussa report that the benefits of running 40 miles per week as versus under 10 miles can be dramatic. Women in the 40 mile club reduce their risk of dying from cardiovascular disease by an estimated 45 percent. Overall, their risk of developing heart disease is an estimated 29 percent less. **
These estimates are based upon the effects of vigorous exercise on cholesterol. To carry cholesterol and fat in the blood, the body wraps them in protein packages called lipoproteins. The family of lipoproteins consists of low density lipoproteins (LDLs) and high density lipoproteins (HDLs). LDLs contain the greatest amount of cholesterol and may be responsible for depositing it in the artery walls. HDLs, on the other hands, contain greater amounts of proteins and small quantities of cholesterol. Said to be the "good" cholesterol, HDLs are thought to remove cholesterol from the artery walls, carrying it to the liver for reprocessing or removal from the body. Research has shown that those with higher levels of HDL have less heart disease.
Williams said the Berkeley Lab study found that HDL levels increased with mileage run, up to at least 40 miles per week. They found a 10 milligrams/deciliter difference in HDL levels between those who run 40 miles/week and those who run less than 10 miles/week.
Said Williams, "We found that the increase in HDL per mile run was the same for women as that previously reported in men. This is despite the fact that women start out with substantially higher HDL levels than men."
Weight loss from running translated to smaller waists and hips. The 10 mile group had an average waist size of 28.3 inches and hips of 37.3 inches. Average waist size in the 40 mile club was 25.8 inches with hips of 34.8 inches.
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. These include age, education, and dietary intake (in terms of alcohol, red meat, fish and fruit).
The researchers also examined whether distance running conferred similar benefits on pre and post-menopausal women and on women who are taking post-menopausal estrogen.
"The benefits apply to both pre and post-menopausal women," said Moussa. "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.
Said Williams, "This study suggest to us that there are substantial health benefits to more vigorous exercise above and beyond the current recommended guidelines. 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."
The Berkeley National Laboratory conducts unclassified scientific research for the U.S. Department of Energy. It is located in Berkeley, California and is managed by the University of California.
** The 45 percent figure assumes a 4.7 percent decrease in the death rate per 1 milligram/deciliter increment increase in HDL levels. The 29 percent figure assumes a three percent decrease in risk per increment.