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Exercise protects postmenopausal women from breast cancer

Study suggests even moderate exercise lowers the risk

Jo Carlowe

Friday, 04 October 2013

A large new study adds to increasing evidence that physical activity reduces breast cancer risk in postmenopausal women.

In new findings, published today online in Cancer Epidemiology, Biomarkers, and Prevention, moderate recreational activity was associated with a 14% lower risk and high physical activity with a 25% lower risk of breast cancer compared to women who were active at the lowest level.

American Cancer Society researchers led by Alpa Patel, compared exercise and breast cancer status in 73,615 postmenopausal women taking part in in the CPS-II Nutrition Cohort, a prospective study of cancer incidence established by the American Cancer Society in 1992. During the 17-year study, 4,760 women in the study were diagnosed with breast cancer.

About one in ten (9.2%) reported no recreational physical activity at the beginning of the study. Among those who were active, the average expenditure was equivalent to 3.5 hours per week of moderately-paced walking. Physically active women engaged primarily in moderate intensity activities, like walking, cycling, aerobics, and dancing rather than vigorous-intensity activities like running, swimming, and tennis. Among all women, 47% reported walking as their only recreational activity. Physically active women tended to be leaner, more likely to maintain or lose weight during adulthood, more likely to drink alcohol, and less likely to currently smoke. They were also more likely to use postmenopausal hormone therapy and to have had a mammogram in the past year.

Among those who reported walking as their only activity, those who walked at least seven hours per week had a 14% lower risk of breast cancer compared to those who walked three or fewer hours per week. Consistent with most prior studies, the most active women had 25% lower risk of breast cancer than the least active. The associations did not differ by hormone receptor status, BMI, weight gain, or postmenopausal hormone use. Also, sitting time was not associated with risk.

"Our results clearly support an association between physical activity and postmenopausal breast cancer, with more vigorous activity having a stronger effect," said Dr. Patel. "Our findings are particularly relevant, as people struggle with conflicting information about how much activity they need to stay healthy. Without any other recreational physical activities, walking on 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."

US guidelines recommend adults get at least two-and-a-half hours per week of moderate-intensity activity, or 75 minutes per week of vigorous-intensity aerobic activity for overall health. But studies indicate less than half of adult women in America are active at these minimum levels.

"Given that more than 60% of women report some daily walking, promoting walking as a healthy leisure-time activity could be an effective strategy for increasing physical activity among postmenopausal women," added Dr. Patel.

doi: 10.1158/1055-9965.EPI-13-0407

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