Exercise Can Lower Your Breast Cancer Risk

The Exercise/Cancer Connection

In the early 1980s, Bernstein was working on a study that looked at the role hormones play in breast cancer. She and her colleagues discovered that women at high risk for the disease had more estrogen in their blood than those at low risk. "We asked ourselves, what could explain this?" she says. "Because I'm a former competitive swimmer, I know that exercise can disrupt the menstrual cycle and even stop menstruation, and I thought it might also affect hormone levels associated with breast cancer. In the first definitive studies on the issue, we found that it does."

Why working out protects us. Physical activity burns fat and also affects ovarian function in premenopausal women, lowering estrogen and progesterone in the blood, explains Bernstein. High circulating levels of these hormones may raise a woman's cancer risk by prompting the breast cells to multiply. In addition, women who exercise regularly have less insulin in their bloodstream; this may also lower levels of female hormones.

Rx for good health. "Exercise reduces your risk not only of breast cancer but also of cardiovascular disease and diabetes," says Bernstein. "Three to four hours a week of brisk walking or any moderate activity, like biking, can help protect you."

It's not just her job, it's her mission. "I've lost friends to breast cancer," says Bernstein. "That keeps me motivated. And given the number of women who are and will be affected by the disease, I know this is something I want to spend my life doing."