Postmenopausal breast cancer risk drops off after starting regular physical activity
Postmenopausal women who in the past 4 years had undertaken regular physical activity equivalent to at least 4 hours of walking per week had a lower risk for invasive breast cancer compared with women who exercised less during those 4 years, according to recently published data.
"Twelve MET-h [metabolic equivalent task-hours] 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," said Agnès Fournier, PhD, a researcher in the Centre for Research in Epidemiology and Population Health at the Institut Gustave Roussy in Villejuif, France. "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."
Postmenopausal women who in the previous 4 years had undertaken 12 or more MET-h of physical activity each week had a 10% decreased risk of invasive breast cancer compared with women who were less active. 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.
"Physical activity is thought to decrease a woman's risk for breast cancer after menopause," said Fournier. "However, it was not clear how rapidly this association is observed after regular physical activity is begun or for how long it lasts after regular exercise stops.”
Fournier explained that this study, published in Cancer Epidemiology, Biomarkers & Prevention (2014; doi:10.1158/1055-9965.EPI-14-0150), answers those questions. Recreational physical activity, even of modest intensity, was found to have a rapid impact on breast cancer risk. However, she explained that the decreased breast cancer risk that they found associated with physical activity was attenuated when activity stopped. 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 E3N, the French component of the European Prospective Investigation Into Cancer and Nutrition (EPIC) study. The mean duration of follow-up was 8.5 years, during which time, 2,155 of the women were diagnosed with a first primary invasive breast cancer.
The total amount of self-reported recreational physical activity was calculated in MET-h per week. 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.