According to a press release issued from the American Cancer Society on Oct. 4, postmenopausal women who moderately exercise for at least 7 hours per week may lower their risk for breast cancer; and those women who are more active may exhibit an even greater risk decrease.
Through data accessed from the American Cancer Society Cancer Prevention Study II Nutrition Cohort, researchers found that of the study’s 73,615 postmenopausal women who were physically active, most engaged in moderate intensity exercise. 47% of these women reported walking as their only activity, the average expenditure equivalent to 3.5 hours per week at a moderate pace.
However, as prior evidence indicates, 3.5 hours/week of moderate physical activity (approx.12 metabolic equivalent hours, or MET-hours) has a low potential for achieving a significant lower risk. According to IDEA, 30–60 minutes of moderate to vigorous (9 – 36 MET-hours) of daily exercise is needed in order to elicit a 20%–40% breast cancer risk reduction. In the current study, a 14 percent decreased breast cancer risk was seen in those who walked at least seven hours per week (>21 MET-hours/week), compared to those who walked three or fewer hours (0–<7 MET-hours/week).
How exercise intensity (moderate vs. vigorous) impacted the results is not clear; however the most active women participants studied (those reporting >42 MET-hours/week physical activity), experienced a 25% lowered breast cancer risk compared to those who were least active.
While prior research supports breast cancer risk reduction for postmenopausal women who lose excess weight and/or maintain a healthy weight, weight status did not impact the results of this recent study. Participants exhibited similar benefits from physical activity whether they were at a healthy weight, overweight, obese, or even if they gained weight during the study.
How exercising lowers breast cancer risk is not fully understood, yet evidence suggests physical activity may prevent tumor development by lowering the levels of hormones that promote cancer growth, while also improving the immune response. The study results did not differ by participant estrogen receptor (ER) status, body mass index (BMI), weight gain, or postmenopausal hormone (PMH) use.
While individual fitness status is a primary consideration in determining appropriate length and intensity of any exercise plan, these recent results support an apparent inverse relationship between physical activity and postmenopausal breast cancer. In the study's press release Dr. Patel comments: “…. walking an average of at least one hour per day was associated with a modestly lower risk of breast cancer. More strenuous and longer activities lowered the risk even more.”
Recreational Physical Activity and Leisure-Time Sitting in Relation to Postmenopausal Breast Cancer Risk, October 2013 issue of Cancer Epidemiology, Biomarkers, and Prevention. Janet S. Hildebrand, Susan M. Gapstur, Peter T. Campbell, Mia M. Gaudet, and Alpa V. Patel, Epidemiology Research Program, American Cancer Society, Atlanta, Georgia
Study Links Moderate Activity to Lower Breast Cancer Risk Study Links Walking to Lower Breast Cancer Risk, Article date: October 4, 2013, By Stacy Simon, American Cancer Society News and Features
Physical Activity and Cancer National Cancer Institute, July 2009