Exercise Lowers Breast Cancer Risk, But Benefits Fade When Activity Stops

A new study has found that postmenopausal women who undertook regular physical activity equivalent to at least 4 hours of walking per week in the last 4 years had a lower risk for invasive breast cancer compared with women who exercised less during those 4 years.

The study, published online ahead of print August 11 in Cancer Epidemiology, Biomarkers & Prevention, found that postmenopausal women who in the previous 4 years had undertaken 12 or more metabolic equivalent task-hours (MET-h) of physical activity each week had a 10% decreased risk of invasive breast cancer compared with women who were less active.

“Twelve MET-h per week corresponds to walking 4 hours per week or cycling or engaging in other sports 2 hours per week, and it is consistent with the World Cancer Research Fund recommendations of walking at least 30 minutes daily,” Agnès Fournier, PhD, a researcher in the Centre for Research in Epidemiology and Population Health at the Institut Gustave Roussy in Villejuif, France, said in a statement. “So, our study shows that it is not necessary to engage in vigorous or very frequent activities; even walking 30 minutes per day is beneficial.”

The study also found that women who undertook this level of physical activity between 5 and 9 years earlier but were less active in the 4 years prior to the final data collection did not have a decreased risk for invasive breast cancer.

“We found that recreational physical activity, even of modest intensity, seemed to have a rapid impact on breast cancer risk. However, the decreased breast cancer risk we found associated with physical activity was attenuated when activity stopped,” Fournier said. “As a result, postmenopausal women who exercise should be encouraged to continue, and those who do not exercise should consider starting because their risk of breast cancer may decrease rapidly.”

Fournier and colleagues analyzed data obtained from biennial questionnaires completed by 59,308 postmenopausal women who were enrolled in the study.

The mean duration of follow-up was 8.5 years, during which time, 2155 of the women were diagnosed with a first primary invasive breast cancer.

The study found that the breast cancer risk-reducing effects of 12 or more MET-h per week of recreational physical activity were independent of body mass index, weight gain, waist circumference, and the level of activity from 5 to 9 years earlier.