(WebMD) -- 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 percent 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 percent. "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.

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, Ph.D., 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 percent. 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, Ph.D., an epidemiologist at the University of North Carolina.

There are also plausible physiological reasons why exercise ought to help, say researchers who have studied the issue. With each menstrual period, the hormone estrogen courses through a woman's body, prompting her breast cells to divide. Experts suspect that the more of these estrogen surges a woman experiences, the higher her risk of breast cancer.

In a number of ways, exercise can reduce the amount of estrogen that the body produces. Young girls who are very active can stave off the onset of menstruation. Adult women who exercise even moderately are likely to ovulate less regularly, even though their periods may continue. Postmenopausal women whose ovaries no longer pump out the hormone still are exposed to a version of estrogen produced by fat stores; exercising enough to hold weight down and convert fat into muscle ought to reduce older women's estrogen exposure, and hence their risk, as well.

What remains a bit murky is exactly how much exercise a woman needs to do and at what time in her life she needs to do it. More seems to be better, but some is better than none. Bernstein's study, for instance, found that women who exercised four hours per week got more protection than those who worked out for only two.

For now, most experts suggest that women hoping to lessen their chances of breast cancer follow the Surgeon General's recommendation of at least 30 minutes of moderate activity -- such as brisk walking -- per day. And, of course, they should continue to get regular breast exams and mammograms, which are still the best protection of all.

As for Becky Boock, she'll be participating this spring in a hometown race that means more to her than any other: A 10K Mother's Day relay that will raise money for breast cancer research. Organizers have dedicated the race to Boock's mother.

October 26, 1999

By Miriam Nelson, Ph.D.

(WebMD) -- Over the past six years, a lot has changed for Neli Stascausky. Having survived breast cancer, the 59-year-old Northern Californian is now enrolled in a study that requires her to exercise regularly and abide by a strict diet, which includes at least five servings of fruits and vegetables a day.

Stascausky admits that the change was difficult at first. She grew up in Argentina, where meat is a staple; she was accustomed to eating beef on a regular basis. She says being part of the study has helped her stick to her diet and may prevent breast cancer from recurring.

Age, sex and family history can all influence a person's risk of developing breast cancer. But of all the risk factors, exercise and diet are the most within your control.

Exercise for prevention

Research is showing that regular exercise helps to prevent many chronic diseases, among them various types of cancer -- including breast cancer. One study from Norway published in a 1997 issue of The New England Journal of Medicine found that women who exercised regularly were 37 percent less likely to develop breast cancer compared with sedentary women, even though the women had the same body weight and body composition.

Regular exercise also helps women to maintain their weight, and this plays a significant role in reducing breast cancer risk. A study by the National Cancer Institute found that 40- to 50-year-old overweight women had twice the risk of developing breast cancer as women who were not overweight.

To reap the benefits of exercise, try the following:

• Get 30 minutes or more of aerobic exercise -- running, brisk walking or biking -- at least five days a week.

• Strength train on nonconsecutive days, two to three times a week. Strength training helps to maintain weight by increasing metabolism, and provides many other health benefits, such as helping to prevent osteoporosis.

• Stretch daily. Stretching helps to maintain flexibility and decrease the risk of injury.

Nutrition for prevention

Good nutrition, like exercise, provides many benefits to your mind and body. And making changes in your diet may make a difference in preventing breast cancer.

Though study results have been conflicting, doctors generally agree that eating more fruits and vegetables may decrease breast cancer risk. Aim to get at least five servings a day. Although this may sound like a lot, keep in mind what a serving is:

• 1/2 cup chopped carrots or broccoli
• 1 cup raw leafy greens
• A small banana or apple
• 1/2 cup chopped strawberries
• 3/4 cup fruit juice

Also, eat a diet that is high in fiber and low in fat, particularly saturated fat. High-fiber foods may help to decrease your risk for breast cancer and other chronic diseases, such as heart disease. Good sources of dietary fiber include oats, bran, beans, grapefruit and apples.

Studies have shown that too much fat in your diet increases the risk of breast cancer. In addition, fat increases your risk for obesity, which also is associated with greater risk of breast cancer.

Limiting alcohol consumption to fewer than two drinks per day is also a good idea. Research suggests that consuming two to five alcoholic drinks per day may increase your risk by up to 40 percent.

Get examined

While regular exercise and a good diet can go a long way toward reducing your risk for breast cancer, nothing can replace regular medical checkups, which can bolster your prevention strategy as well as detect the disease early.

Doing breast self-exams, at the same time each month after the age of 20, is also important. If you are between the ages of 20 and 39, you should also have your physician do a breast exam once every three years. According to the National Cancer Institute, women ages 40 and older should have a mammogram every one to two years. The institute recommends that women who are at particularly high risk for breast cancer consult their physician on how often they should have a mammogram. Remember: Early detection of breast cancer can save lives.