Exercise and Breast Cancer

Women who exercise three to four hours a week may reduce their risk of getting breast cancer by as much as 30-40%.

Nearly 30 studies have shown that moderate to vigorous exercise reduces the risks as much as provided by the drug Tamoxifen — but without all of the adverse side effects.

Guidelines for cancer prevention, which were recently developed by the American Cancer Society and the World Health Organization’s International Agency for Research on Cancer, focus on physical activity, weight control and nutrition — rather than drug therapy.

According to both groups, the evidence linking exercise to reducing the risk of breast cancer is convincing; therefore, they recommend women engage in at least 30 minutes of moderate to vigorous exercise per day.

According to scientists, this link is attributed to hormones. Exercise reduces the levels of estrogen, testosterone, insulin and growth factors — which could either cause breast cancer or prompt it to grow faster and larger. Those at risk for breast cancer are women with high levels of these hormones in their blood.

The relationship between C-peptide, a marker of insulin production, and the risk of breast cancer was examined by a team of researchers from Harvard University. 32,000 women participated in the study.

C-peptide was measured form 463 women who developed breast cancer and then compared with C-peptide level blood samples in women who did not have breast cancer.

Results showed women with the highest C-peptide levels had a 70% greater chance of developing cancer than women with the lowest levels. High C-peptide levels are typically found in overweight, obese and inactive women. Other studies show insulin levels drop after exercise sessions, thus resulting in immediate benefits.

SOURCE: “Preventing Breast Cancer,” ABC News, April 15, 2002.