An exercise in risk reduction

Postmenopausal women who make working out a habit are better able to keep breast cancer at bay

LOS ANGELES, July 7, 1999 -- Regular exercise over a lifetime significantly reduces the risk of breast cancer in postmenopausal women -- especially if those women maintain a relatively stable weight throughout their adulthood -- according to a study conducted by researchers at the University of Southern California that is being published in this week's issue of the British Journal of Cancer.

A number of previous studies have found a link between exercise and a reduction in breast cancer risk for younger women. Perhaps the most prominent and often cited of these studies -- a 1994 paper published by Leslie Bernstein, Ph.D., and colleagues at the USC/Norris Comprehensive Cancer Center -- found that women aged 40 years or younger who spent four or more hours exercising each week over their reproductive years reduced their risk of breast cancer by more than half.

The problem, it seems, was that the concerns of those women most at risk for breast cancer -- older women who have gone through menopause -- were not addressed by those results.

"When we published the first paper, the questions we were asked most frequently were, 'What about postmenopausal women?'" says Bernstein. "Women wanted to know, 'Will exercise protect me later in life?' 'Is it too late to start exercising when I'm older?' And we didn't have an answer for them at that time."

Now they do. In their newly published paper, Bernstein, first author Catherine Carpenter, Ph.D., Ronald Ross, Ph.D., and Annlia Paganini-Hill, Ph.D., all from USC's Department of Preventive Medicine, showed that exercise can indeed protect postmenopausal women from the disease.

"Basically, we conducted a case-control study assessing the effects of lifetime exercise on the breast cancer risk of postmenopausal women who were between the ages of 55 and 64," says Carpenter. "We found that among women who exercised vigorously throughout their adolescence and adult years for at least three hours each week, the risk of breast cancer was 45 percent lower than sedentary women." When the researchers looked at only those women who had maintained a steady weight during adulthood -- those who weighed 17 percent or less than they weighed at age 18 -- that risk reduction jumped to 55 percent.

It is fairly well known that women who gain a significant amount of weight as adults are at higher risk for breast cancer, notes Bernstein. What was somewhat surprising was that when the researchers looked only at the women with relatively stable weight, exercise had dramatic effects on breast cancer risk that were independent of the women's weight. Yet, among those women who had gained a lot of weight, they found essentially no reduction in their risk at all, regardless of how much they exercised. "Exercise didn't really protect women who gained weight," says Carpenter. "But among women who maintained a stable weight, the breast cancer risk was substantially reduced."

Because women want to know how many years they should exercise and for how many hours per week, the USC researchers examined the question. In order to reap the greatest breast-health benefits from exercise, women need to spend at least four hours a week in vigorous exercise and do this for at least 12 years of their lives. "That's a pretty big commitment," notes Bernstein. "For women maintaining an exercise program at this level, exercise is an important component of their lives."

And that commitment needs to start fairly early on for it to really pay off. Women who were sedentary most of their lives and then started to exercise later didn't see much of a reduction in risk. "It's your lifetime practice that really makes a difference," says Carpenter. "It's great to start now, but it's much better to have made exercise and maintaining a stable weight your lifetime health practice."

The take-home message? "Several measures of exercise all tell the same story -- maintain your weight and exercise," says Carpenter. "If you can maintain your weight through exercise, that's great. Together, they are a much more potent combination."

CL Carpenter, RK Ross, A Paganini-Hill and L Bernstein, "Lifetime exercise activity and breast cancer risk among post-menopausal women," British Journal of Cancer, July 9, 1999.