Exercise Helps Prevent Breast Cancer

April 23 -- Most women would be willing to do just about anything to avoid breast cancer, a sometimes disfiguring, potentially fatal disease.

One way to significantly reduce breast-cancer risk is as close as the sneakers in your closet.

Nearly 30 studies have shown that women who exercise at moderate to vigorous levels for three or more hours per week reduce their risk of getting breast cancer by 30 percent to 40 percent.

That's about as much reduction in risk as provided by the drug tamoxifen, but without the side effects.

The American Cancer Society and the World Health Organization's International Agency for Research on Cancer recently developed guidelines for cancer prevention focusing on physical activity, weight control and nutrition.

They both conclude that the evidence linking exercise to a reduced risk for breast cancer is convincing, and both recommend that women engage in moderate to vigorous exercise for at least 30 minutes per day, preferably more for optimal benefit.

Hormones Are the Link

Scientists believe that hormones are the link between exercise and breast-cancer protection. Exercise reduces levels of estrogen, testosterone, insulin, and growth factors, all of which may either cause breast cancer or prompt it to grow faster and larger. Women with high levels of these hormones in their blood have a high risk of developing breast cancer.

Research recently presented at the American Association for Cancer Research annual meeting in San Francisco may shed some additional light. Dr. Celia Byrne and colleagues (from Harvard University) studied the relationship between C-peptide, a marker of insulin production, and risk for breast cancer in the Nurses' Health Study, which involves more than 32,000 women.

They measured C-peptide in blood from the 463 women who developed breast cancer and compared it with blood C-peptide levels in a sample of women who did not develop the disease.

They found that those who had the highest C-peptide levels had a statistically significant, 70 percent greater chance of developing breast cancer compared with women who had the lowest levels.