Exercise May Cut Breast Cancer Risk

Regular exercise in adolescence and young adulthood may help cut a woman's risk of developing breast cancer before menopause, according to a US study published.

The women who were the most physically active were 23 percent less likely to develop premenopausal breast cancer than the women who got the least exercise, the researchers wrote in the Journal of the National Cancer Institute.

High levels of exercise from ages 12 through 22 contributed the most to the protective effect, the researchers said.

"The more activity, the greater the benefit," study leader Dr. Graham Colditz of Washington University School of Medicine and Barnes-Jewish Hospital in St. Louis said in a telephone interview.

Previous studies showed that regular exercise in adulthood leads to at least a 20 percent lower risk of breast cancer after menopause, the researchers said. Research on exercise and breast cancer risk before menopause had produced inconsistent results, they said.

The researchers said the new study indicated women need regular physical activity starting at a young age to comparably lower their risk of breast cancer before menopause. They called their study the largest and most detailed examination to date of the impact of exercise on early breast cancer risk.

Colditz and colleagues studied 65,000 registered nurses aged 33 to 51 who reported in 1997 how much leisure-time physical activity they had done since the age of 12.

After six years of follow-up, 550 of the women were diagnosed with breast cancer.

The women classified as most active did the equivalent of running for 3.25 hours a week or walking for 13 hours a week.

"It's not marathon running. Any team sport will get you to that level of activity -- and it doesn't even have to be a team sport," Colditz said.

Women who exercised regularly -- but not as much as the most-active group -- also had a reduced risk for breast cancer, but not as much as the top group, Colditz said.

The benefit provided by exercise was not associated with a particular sport or intensity, Colditz added.

About a quarter of all breast cancer cases are diagnosed in women before menopause and these can be more aggressive and harder to treat than breast cancer in older women.

Protection against breast cancer is just one of many benefits of exercise, Colditz said. "It protects against diabetes, heart disease, stroke. Clearly it's good for bones to protect against osteoporosis and fractures. There is a clear benefit across many of the chronic diseases."

He said there are several hormone-related hypotheses to explain how exercise may cut breast cancer risk. A leading idea is that physical activity can cut a woman's lifetime exposure to estrogen, a hormone strongly implicated in breast cancer.

Breast cancer is the leading cause of cancer death among women worldwide, killing an estimated 465,000 women annually, according to the American Cancer Society. About 1.3 million women are diagnosed annually worldwide.