Clinical Briefs

With Comments from John La Puma, MD, FACP

Aerobic Exercise and Breast Cancer Risk

March 2000; Volume 3: 35

Source: Rockhill B, et al. A prospective study of recreational physical activity and breast cancer risk. Arch Intern Med 1999;159:2290-2296.

Increased physical activity has been hypothesized to prevent breast cancer, largely by reducing cumulative lifetime exposure to circulating ovarian hormones.

We analyzed data from the Nurses’ Health Study, a prospective study of women aged 30-55 years in 1976. In 1980 and on subsequent surveys, women were asked about the average number of hours per week spent in various moderate and vigorous recreational physical activity during the past year. We computed a "baseline-only" (1980) measure of hours per week of physical activity, as well as a cumulative average measure that used updated reports on physical activity.

During 16 years of follow-up, we identified 3,137 cases of invasive breast cancer (1,036 premenopausal and 2,101 postmenopausal women). Data were analyzed by use of multivariate pooled logistic regression to produce relative risks of breast cancer, and the associated confidence intervals.

Women who were more physically active in adulthood had a lower risk of breast cancer than those who were less physically active. Comparing those who reported engaging in moderate or vigorous physical activity for seven or more hours per week with those who engaged in such physical activity for less than one hour per week, the relative risk was 0.82 (95% confidence interval [CI] 0.70-0.97), using the cumulative average updating. The dose-response trend was statistically significant (P = 0.004). Using the baseline-only measure of physical activity produced slightly weaker relative risks. Higher levels of adult physical activity afford modest protection against breast cancer.


In this epidemiological study, Harvard-associated investigators show once again that a few hours of prevention is worth more than a few minutes. And time does seem to be the relevant variable, one which Americans have less of every day. Women concerned about what they can do to reduce their risk for breast cancer may have to take the long road, but it looks like it may lead where they want to go.

The evidence for breast cancer risk reduction techniques is much better than the evidence for breast cancer treatment or prevention against recurrence. Nevertheless, an eight-week pilot study of an exercise-diet intervention in breast cancer patients in Seattle (Cancer Epidemiol Biomarkers Prev 1998;7:477-481) indicated that Stage 1 and 2 breast cancer patients who attended aerobic exercise sessions three times weekly and ate a low-fat diet (20% calories from fat), lost weight, inches, body fat, and blood pressure points, and gained lean body mass. Obesity, of course, is a risk factor for breast cancer development.


Women, especially those at risk for breast cancer, should include regular aerobic exercise as a central part of their prevention regimen.