Exercise Cuts Invasive Breast Cancer Risk in Older Women

Moderate exercise can cut the risk of breast cancer in postmenopausal women.

A moderate amount of regular exercise results in a lower risk of invasive breast cancer among postmenopausal women, according to a new study published in Cancer Epidemiology, Biomarkers & Prevention. Postmenopausal women who engaged in at least 4 hours of walking (12 metabolic equivalent task-hours [MET-h]) per week for 4 years had a 10% lower risk of the disease compared with postmenopausal women who exercised less frequently in the same time period.

Keeping up with an exercise regimen appeared to be important. Among the women who engaged in more than 12 MET-h of exercise per week for 5 to 9 years prior, those who subsequently became less active had a significantly increased risk of breast cancer compared with women who continued to exercise (hazard ratio = 1.16). Compared with the least active women, those women whose exercise levels declined in the last 4 years of the study had no significantly decreased risk of breast cancer.

“Physical activity-including walking and cycling-even of modest intensity, was quite rapidly associated with a decrease in breast cancer risk. [This] was, however, attenuated when activity [stopped],” said study author Agnès Fournier, PhD, of the Centre for Research in Epidemiology and Population Health at the Institut Gustave Roussy in Villejuif, France.

“The main takeaway for women is if they already exercise, they must be encouraged to continue in order to keep the benefit of physical activity regarding decreased breast cancer risk,” said Fournier. “For those women who do not exercise, it is worth starting! Their risk of breast cancer may decrease rapidly.”

Prior studies had shown a positive impact of regular exercise on breast cancer risk after menopause, but it was not clear how soon the impact can be seen; what frequency, duration, and intensity is needed to reduce risk; and how long the impact of exercise lasts after physical activity is stopped.

Fournier and colleagues analyzed data from 59,308 postmenopausal women who were followed from 1993 to 2005 through questionnaires as part of the E3N, the French component of the European Prospective Investigation into Cancer and Nutrition (EPIC) study. Among these women, 2,155 were diagnosed with invasive breast cancer.

The benefit of 12 MET-h of exercise per week did not vary by estrogen receptor/progesterone receptor status. The reduction in risk was seen for women across a range of body mass indices, weight changes, and waist circumferences.

Twelve MET-h of exercise per week is consistent with the World Cancer Research Fund recommendations of walking at least 30 minutes daily.

The strengths of this study included its prospective analysis, large cohort size, and large number of breast cancer cases, as well as detailed information on the study subjects. Still, this is a self-reported study and should be repeated in other populations. “Because the women participating in the cohort are fairly slender teachers, our results should be replicated in populations with different genetic, anthropometric, and occupational characteristics,” concluded the authors.

According to Fournier, the follow-up of the E3N study group, born between 1925 and 1950, is continuing and the researchers will conduct further analyses on this aging cohort. The team is also building a complimentary cohort, E4N-the children, children’s spouses, and grandchildren of the E3N participants. “We will be able to investigate the influence of environmental, genetic, and epigenetic factors during different periods of life on disease risk and progression, including physical activity and cancer risk,” Fournier told Cancer Network.