Exercise Cuts Breast Cancer Risk

Even moderate workouts are enough to do the trick

TUESDAY, Sept. 9, 2003 (HealthDayNews) -- Here's another reason to put down that remote control and get moving: Research shows that moderate, simple exercise reduces the risk of breast cancer -- even if you don't start until your menopause years.

In a study published in the Sept. 10 issue of the Journal of the American Medical Association, researchers from the Fred Hutchinson Cancer Center in Seattle confirmed earlier findings showing that exercise does indeed reduce the risk of breast cancer.

But going one step farther, they also report that even moderate physical activity, such as 30 minutes of walking three times a week, offers substantial protection as well -- something previous studies have not shown.

"The important news here is that regular exercise allows a woman some measure of control over her personal risk profile for breast cancer. Plus, as long as the exercise is consistent, she doesn't even have to work that hard to get the benefits," says study author Dr. Anne McTiernan, a member of Fred Hutchinson's Public Health Sciences Division and director of the center's Prevention Center.

What's more, says McTiernan, the benefits of exercise extend to women at highest risk of the disease. "Women with a family history of breast cancer, those who never had children, and women using HRT (hormone replacement therapy) all saw a reduced risk of breast cancer in conjunction with exercise," McTiernan says.

Dr. Steven Goldstein, a professor of obstetrics and gynecology at New York University Medical Center, says that while the study results are promising, they also warrant a few words of caution.

"This is an observational study, and the women who experienced the protective effects of exercise might well have been women who generally took better care of themselves overall, thus reducing their risk factors in other ways," Goldstein says.

So, while exercise confers many benefits -- such as reducing risks of heart disease, high blood pressure, diabetes and more -- Goldstein also urges women not to abandon other important self-care measures. They include regular mammograms, monthly self-breast exams, reduced consumption of alcohol and fat, and no cigarettes.

"Exercise, absolutely, but don't rely on that alone for breast health and protection," Goldstein says.

The new study was based on data from the Women's Health Initiative, (WHI) a major research project started in 1991 that follows tens of thousands of women, in an effort to identify risk factors for various diseases -- including breast cancer.

This particular arm of the study involved more than 74,000 postmenopausal women between the ages of 50 and 79, with a broad ethnic, racial and geographic profile, from 40 testing sites nationwide. At the start of the study, each woman completed a survey documenting, among other health factors, her personal exercise history at ages 18, 35 and 50, as well as current level of activity.

In a follow-up period of 4.7 years, the researchers documented 1,780 breast cancers. McTiernan and her group then investigated the exercise habits of these women, and compared them to those who did not develop breast cancer.

The result: When compared to sedentary women, those who performed moderate exercise -- such as walking or swimming -- from 1.25 to 2.5 hours a week experienced an 18 percent decrease in the incidence of breast cancer. Those who exercised 10 hours or more a week saw only slightly more protection -- up to a 22 percent decreased risk.

McTiernan says risks were reduced even when various contributing factors for breast cancer were figured into the equation, such as smoking and drinking alcohol.

The study also found those women who benefited most from exercise were the ones who had the least body fat. McTiernan reports that women with a body mass index (BMI) of 24 or less saw the greatest decreased risk of breast cancer -- up to 32 percent -- while those with a BMI of 28 or more saw no risk reduction. A body mass index greater than 25 is considered overweight; a BMI that exceeds 30 is termed obese.

Currently, researchers aren't sure how or why exercise exerts its protective effects against breast cancer. However, McTiernan hypothesizes that a reduction in body fat is the key. Studies have shown that excess fat cells help convert androgens and other hormones into excess estrogen, long suspected of having links to breast cancer.

McTiernan also says that exercise reduces the amount of estrogen circulating in the blood, offering additional protection.

Completing the circle, other studies have shown that exercise can also help keep insulin levels low, which, in turn, helps reduce body fat.

More information

To learn more about exercise and breast cancer, check with the National Institutes of Health. For more about risk factors for breast cancer, visit the American Cancer Society.

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