PHILADELPHIA — Postmenopausal women who were very active or walked for at least seven hours a week had a reduced risk for breast cancer, according to a study published in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research.
Women who engaged in at least an hour of vigorous physical activity every day had a 25 percent lower risk for breast cancer, and those who walked for at least seven hours a week had a 14 percent lower risk for breast cancer, in this study of 73,615 postmenopausal women.
"We examined whether recreational physical activity, specifically walking, was associated with lower breast cancer risk. Given that more than 60 percent 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," said Alpa Patel, Ph.D., senior epidemiologist at the American Cancer Society (ACS) in Atlanta, Ga. "We were pleased to find that without any other recreational activity, just walking an average of one hour per day was associated with lower risk of breast cancer in these women."
After making adjustments to the data, the researchers determined that the observed benefits of physical activity and walking were not influenced by body type (BMI and weight gain) or hormonal status (postmenopausal hormone use and estrogen receptor status).
This is the first study to report a lower risk for breast cancer among this demographic associated specifically with walking, according to the authors.
"Current guidelines recommend that adults should strive to get at least 2.5 hours per week of moderate-intensity activity, or 75 minutes per week of vigorous-intensity aerobic activity for overall health. Higher levels of activity may provide greater benefit for breast cancer prevention," said Patel.
Patel and colleagues identified 73,615 postmenopausal women from a large cohort of 97,785 women aged 50 to 74 years, recruited between 1992 and 1993 to the Cancer Prevention Study-II Nutrition Cohort, a prospective study of cancer incidence established by the ACS. Participants completed a self-administered questionnaire on demographic, medical, and environmental factors during enrollment. They also completed follow-up questionnaires every two years between 1997 and 2009, to update information on new exposures and newly diagnosed cancers.
All participants provided information on the average number of hours they spent on various physical activities including walking, jogging, swimming, playing tennis, bicycling, and performing aerobic exercises every week, and the number of hours spent in leisure time sitting, including watching television and reading. The researchers calculated the total hours of metabolic equivalent (MET) per week for each participant, which is a ratio of the energy spent during a specific activity to the resting metabolic rate.
Among the study participants, 4,760 of them subsequently developed breast cancer.
The researchers found that about 9.2 percent of the participants did not partake in any physical activity, and about 47 percent of them reported walking as their only activity. The median MET expenditure among active women was 9.5 MET hours per week, which translates to 3.5 hours of moderately-paced walking.
They found that the most active women with 42 MET hours per week or more (at least one hour of vigorous activity every day) had a 25 percent lower risk for breast cancer compared with women who were least active, with less than seven MET hours per week (e.g., moderately-paced walking for two hours a week). Among women who reported walking as their only activity, those who walked for seven hours or more per week had a 14 percent lower risk for breast cancer, compared with those who walked for three hours or less. They did not find any risk associated with time spent sitting.