If tests with rats are any indication, it's conceivable that exercise even could help prevent breast cancer.

While it is generally believed that regular physical activity can lower the risk of heart disease and high blood pressure, there has been little research on its impact on cancer risk. Now, the idea is gaining interest among researchers.A University of Illinois study has found that regular, light-to-moderate, aerobic exercise reduced breast cancer risk in laboratory rats.

Rats on a high-fat diet, already associated with breast cancer, were fed a chemical known to induce the cancer. One group was put on treadmills to simulate the level of exercise of a human walking briskly five days a week for a half-hour a day.

The number of rats developing breast tumors was 35-40 percent lower than those rats who didn't exercise at all, reported Donald Layman, a nutritional biochemist at the university.

Acknowledging that there's no certain way to compare human exercise and breast cancer, Layman nonetheless suggested there's a "good chance that aerobic workouts may reduce the incidence of breast cancer," and called for more research on the subject.