Researchers have uncovered a decreased risk of breast cancer among women who walk 7 or more hours per week compared with women who walk for 3 hours or less per week.
Although epidemiologic evidence supports an inverse relationship between physical activity and postmenopausal breast cancer, it has been unclear whether such associations exist for walking and other moderate activities, and whether associations differ by estrogen receptor (ER) status, body mass index (BMI), adult weight gain, or use of postmenopausal hormones (PMH). The relationship between time spent sitting and breast cancer also has been unclear, pointed out Alpa V. Patel and colleagues in Cancer Epidemiology, Biomarkers & Prevention (2013;22:1906-1912).
To learn more about how recreational physical activity and leisure-time sitting affected breast cancer risk in postmenopausal women, Patel and team analyzed data from 73,615 postmenopausal women in the American Cancer Society Cancer Prevention Study II Nutrition Cohort. A total of 4,760 of those women received a diagnosis of breast cancer between 1992 and 2009.
Metabolic equivalent (MET), an estimate of the ratio of the energy expenditure during a specific activity to the resting metabolic rate, was calculated for each woman. Physically active women engaged primarily in such moderate-intensity activities as walking, cycling, aerobics, and dancing rather than such vigorous-intensity activities as running/jogging, swimming, tennis, and racquetball. Current guidelines recommend at least 150 minutes per week of moderate-intensity activity or 75 minutes per week of vigorous-intensity aerobic activity for adults to maintain overall health.
The most active women—those reporting more than 42 MET-hours/week of physical activity—had a 25% lower risk for breast cancer than did the least active women, who reported zero to less than 7 MET-hours/week.
Nearly half the women (47%) stated that walking was their only recreational activity. In this group, those who walked at least 7 hours per week were 14% less likely to develop breast cancer than were women who walked no more than 3 hours per week. The associations did not differ by ER status, BMI, weight gain, and PMH use. Sitting time did not affect risk.
“Without any other recreational physical activities, walking on average of at least 1 hour per day was associated with a moderately lower risk of breast cancer,” summarized Patel in a statement issued by the American Cancer Society. “More strenuous and longer activities lowered the risk even more.”