Lifelong Physical Activity Lowers Breast Cancer Risk

ORLANDO—Women in all ethnic groups who have spent their lives exercising, performing heavy household chores, or tackling a physically strenuous job had a lower risk of breast cancer than their more sedentary counterparts, according to a poster presented at the Era of Hope Department of Defense Breast Cancer Research Program meeting. "We were pleased with the results," said principal investigator Esther M. John, PhD, director of epidemiology research, Northern California Cancer Center, Union City. "It’s a message we can give women to help prevent breast cancer, and there are other health benefits to physical activity."

The researchers personally interviewed 1,326 women, aged 35 to 79, diagnosed with invasive breast cancer between 1995 and 1998, and 1,657 controls found through random-digit dialing. The cohorts were equally divided, with approximately one third each Hispanic, non-Hispanic white, and African American. All came from the San Francisco Bay area.

The women were asked about moderate and vigorous physical activity, including participation in sports, if they walked or bicycled to school or work, exercise, household and outdoor chores, and occupational activities. Responses from all the categories were combined to arrive at an average measure of physical activity.

Among the women who had the highest level of physical activity, premenopausal women had a 26% lower risk of breast cancer and postmenopausal women a 19% lower risk, Dr. John reported. Women who were not overweight (body weight index of 25 or less) had a slightly greater risk reduction than overweight women. Risk reduction was not limited to vigorous exercise but was also present for moderate activity. Risk reduction results in the three ethnic groups were similar for similar amounts of activity.

Hispanic women had the highest level of lifetime physical activity, followed by African Americans and non-Hispanic whites, Dr. John said.

She noted that Hispanic women have a lower incidence of breast cancer: In the San Francisco Bay area during the years of the study, the rates per 100,000 for women aged 35 to 49 were 90 for Hispanics, 105 for African Americans, and 135 for non-Hispanic whites.

Dr. John estimated that differences in physical activity could explain a small percentage (13%) of the difference in breast cancer incidence between Hispanic and non-Hispanic white women younger than age 50. But physical activity was not a factor in the incidence disparity between African-American women and non-Hispanic white women.

"We found that women who are physically active have a reduced risk of breast cancer, something that other studies have found, so our study is consistent with previous reports," Dr. John concluded. "The other important finding is that the physical activity doesn’t have to be exercise. Some women get a lot of physical activity from household chores or jobs, and that kind of activity seems to be equally important. The bottom line is, go out and be physically active. Physical activity is modifiable. We can change lifestyle."