Does exercise prevent breast cancer?

Philip J. Goscienski, M.D.

October 2006

Women with higher levels of physical activity, especially during adolescence and early adult life, have a lower risk of breast cancer than women who have been sedentary. That conclusion comes from multiple studies and it adds yet another reason for women of all ages to make exercise a high priority in their daily routine.

Japanese women living in their native country have one of the lowest rates of breast cancer on the planet. Even among them however, it's clear that two bouts of vigorous exercise a week lower their risk of breast cancer, especially for those who are overweight. Women of Japanese ancestry living in the United States develop breast cancer with almost the same frequency as Caucasians but physical activity protects them from this disease as well.

Exercise may lower the risk of breast cancer because it helps to control weight gain. Obese women increase their risk of breast cancer by as much as five times, possibly because fat cells produce estrogen-like factors that promote cancer in hormone-sensitive cells within the breast. We may be raising a generation that is at high risk because adolescent girls, especially among the Hispanic and African-American populations, have become increasingly less active and more obese.

Exercise might even improve survival in women with breast cancer. In a study from the University of North Carolina researchers found that among women who were overweight or obese at the time of diagnosis, but who engaged in moderately intense physical activity in the preceding year, survival increased by 30 percent compared to women who exercised little.

In a sense we are all living in an artificial environment, that is, one that we are not as well adapted to as were humans of thousands of generations ago. Back then women didn't get hormones in their meat or by prescription. The only food additives were dirt particles. They ate loads of protective antioxidants with all their fruits, nuts and vegetables, even though they needed fewer than we do. They didn't have to contend with pollutants, a thinning ozone layer or continual stress. Even moderate alcohol intake increases risk and Stone Agers never touched the stuff.

There is a window of cancer-proneness that is growing wider among today's young women and that may influence the number of cases that will arise in the next few decades. Girls are maturing earlier and having babies later. The woman who has a short interval between menarche (the onset of regular menstrual periods) and first full-term pregnancy has about half as much chance of getting breast cancer as the woman who has never been pregnant. That may be because the breast does not fully mature until the end of a normal pregnancy and an immature breast, as noted, is more susceptible to cancer-causing agents like those in tobacco smoke.

Breast cancer may not be entirely avoidable, especially among women that have a strong family history of the disease. It's possible to lower the risk by following some Stone Age principles: maintain normal body weight, stay physically active, eat plenty of fruits and vegetables, and don't smoke.

Philip J. Goscienski, M.D. is the author of Health Secrets of the Stone Age, Better Life Publishers 2005. Contact him at