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Fight Fat, Fight Cancer

Regular exercise helps keep breast cancer at bay.

WebMD Feature

March 13, 2000 (Cambridge, Mass.) -- Becky Boock has always been a devoted athlete, reveling in the thrill of the race. A former competitive runner and swimmer, the 19-year-old Canadian races in at least three triathlons each summer. Now she has an additional reason to keep moving: Boock recently lost her mother to breast cancer.

"Exercise is both an outlet and a way of prevention for me," she says. "I can only hope my healthy lifestyle will help me stay safe." Boock isn't alone in this hope.

Even women who haven't lost a relative to breast cancer often fear this disease most. And until recently, experts haven't been able to offer solid evidence to those wondering whether lifestyle factors such as exercise might reduce their risk.

But now that's changing. After years of conflicting findings, a new consensus is emerging. It's very good news for women who already work out, as well as for anyone who's looking for a new reason to get motivated: Regular exercise, it seems, really can cut a woman's chances of getting breast cancer.

The latest study, published in the January 19 issue of the Journal of the National Cancer Institute, found that active women were about 30% less likely to get the disease. Last October, Harvard University researchers published findings from the large-scale Nurses' Health Study showing that regular exercisers cut their risk by 20%. "If you take all the data on balance, there is a moderate reduction of risk," says Beverly Rockhill, Ph.D., lead author of the Harvard study.

Scientific Tomato-Throwing

The data haven't always pointed in this direction. Indeed, in an earlier analysis of Nurses' Study data, Rockhill and her colleagues were unable to show that exercise offered any shield. "We found no protective effect whatsoever," Rockhill said at the time. Other researchers cited in a review paper published in the January 21, 1998 issue of the Journal of the National Cancer Institute found that exercise reduced risk before -- but not after -- menopause. Still others cited in that paper found precisely the opposite. And at least one study reviewed there showed that exercise raised risk.

Why all the back-and-forth? Mainly, researchers say, because it's tough to pinpoint exactly how much a woman has been exercising during her lifetime. Many studies have asked women how much they exercised at a particular time, then extrapolated that amount over several years. "It's vitally important that women be asked about their lifetime history of exercise," says Leslie Bernstein, PhD, an epidemiologist at the University of Southern California.

Bernstein pioneered a way of measuring lifelong activity that relies on detailed interviewing. In one important study that used this method, published in the September 21, 1994 issue of the Journal of the National Cancer Institute, Bernstein found that a regular exercise habit cut the risk of breast cancer by a whopping 40%. Bernstein's methods give her study more weight than many of the others, and support the case for exercise's protective effect, says Marilie Gammon, PhD, an epidemiologist at the University of North Carolina.

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