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Increased Physical Activity and Walking Reduces Breast Cancer Risk

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Key Points

  • A large epidemiology study of 73,615 postmenopausal women found that women who participated in at least 1 hour of vigorous physical activity every day had a 25% lower risk of breast cancer, and those who walked for at least 7 hours per week had a 14% reduced risk of breast cancer, compared with less active women.
  • The benefits derived from increased physical activity and walking were not influenced by body type or hormonal status.
  • Less than half of adult women are active at minimum levels recommended in current guidelines.

A large epidemiology study of postmenopausal women by researchers at the American Cancer Society (ACS) has found that women who participated in at least 1 hour of vigorous physical activity every day had a 25% lower risk of breast cancer, and those who walked for at least 7 hours per week had a 14% reduced risk of breast cancer. In addition, the benefits derived from increased physical activity and walking were not influenced by body type, including body mass index and weight gain, or hormonal status, such as postmenopausal hormone use and estrogen receptor status. The study is published in Cancer Epidemiology, Biomarkers & Prevention.

“I was very excited to see that simply going for a leisurely walk an hour a day is beneficial for lowering breast cancer risk,” said Alpa V. Patel, PhD, Senior Epidemiologist at the ACS and a coauthor of the study. “With more vigorous activity you do increase that benefit, but when we think about over 230,000 women being diagnosed with breast cancer, a 14% lower risk for women is substantial.”

Study Methods and Findings

The researchers identified 73,615 postmenopausal women from a large cohort of 97,785 women ages 50 to 74, recruited between 1992 and 1993 to the Cancer Prevention Study-II Nutrition Cohort, a prospective study of cancer incidence established by the ACS. The study participants completed a self-administrated questionnaire on demographic, medical, and environmental factors during enrollment and updated their exposure information every 2 years between 1997 and 2009 to ascertain newly diagnosed cancers. Response rates were high at 88% or more. Among the study participants, 4,760 subsequently developed breast cancer.

All study participants provided information on the average number of hours they spent on physical activities, including walking, jogging, swimming, playing tennis, bicycling, and performing aerobic exercises every week and the number of hours spent in leisure time, including watching television and reading. The researchers then calculated the total hours of metabolic equivalent (MET)—the ratio of the energy spent during a specific activity to the resting metabolic rate—per week for each participant. They found that about 9.2% of the study volunteers did not participate in any physical activity, and about 47% 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.

Women with 42 or more MET hours per week (at least 1 hour of vigorous activity every day) had a 25% lower risk for breast cancer compared with women who were least active, with less than 7 MET hours per week (moderately paced walking for 2 hours a week).

Among the women who reported walking as their only activity, those who walked for 7 or more hours per week had a 14% lower risk of breast cancer, compared with women who walked for 3 hours or less. The researchers did not find any risk associated with time spent sitting.

According to the Centers for Disease Control and Prevention, current physical activity guidelines for adults call for at least 150 minutes per week of moderate-intensity or 75 minutes per week of vigorous-intensity aerobic activity for overall health. According to the study, less than half of American adult women are active at these minimum levels. As a result, an even smaller proportion of women likely achieve the higher levels of physical activity thought necessary for breast cancer risk reduction.

The study authors reported no conflicts of interest. 

The study was funded by the American Cancer Society.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.


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