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Walking more may help lower the risk of breast cancer, study finds

October 21, 2013

Walking more may help women lower their risk of developing breast cancer.

Women who walked at least seven hours a week had 15 percent less risk of developing breast cancer than those who walked less than three hours a week.
[Photo courtesy of Women's Heart Organization]

By Andy Koopmans

Walking more may help women lower their risk of developing breast cancer – even if they don’t engage in more vigorous exercise, a new study suggests.

Women who walked at least seven hours a week – typically an hour a day – had 15 percent less risk of developing breast cancer than those who walked less than three hours a week, according to a large study published this month in Cancer Epidemiology, Biomarkers & Prevention.

The study drew on health and medical records of more than 73,600 women aged 50 to 73 from the American Cancer Society Cancer Prevention Study II who enrolled in the study in the early 1990s. Follow-up was conducted via questionnaires every two years for nearly two decades, with participants reporting on their exercise and leisure time habits.

Researchers examined total recreational physical activity, walking, and leisure-time sitting, as well as BMI, adult weight gain and postmenopausal hormone use and estrogen receptor status. Of the study participants, 47 percent reported walking was their only recreational activity.

Nearly 5,000 of the women developed breast cancer over the duration of the study.

The new finding adds to a growing body of research indicating that exercise can lower the risk of breast cancer. “Physical activity has consistently been associated with lowered risk of postmenopausal breast cancer,” said Dr. Anne McTiernan, director of the Fred Hutchinson Cancer Research Center’s Prevention Center and a member of its Public Health Sciences Division.

McTiernan has worked on several studies including one published in the Journal of the American Medical Association (JAMA) in 2003 that showed that moderate-intensity exercise lowers risk for breast cancer in postmenopausal women. That study used  data from the Women’s Health Initiative, which indicated that sustained exercise is beneficial, even if moderate.

“We found that total amount of exercise was more important than specific type or intensity,” she said. “Most women choose walking as their type of exercise. Bottom line—you don’t have to be an athlete to benefit from exercise in lowering breast cancer risk. The current recommendation is to get at least 150 minutes of moderate-intensity exercise per week, with more benefit for additional time exercised.”

Weight control and exercise a powerful combo

Although the American Cancer Society’s new study showed walkers reduced their risk of breast cancer irrespective of weight as a factor, studies McTiernan has been involved with, including randomized controlled trials, have shown that being a healthy weight can  reduce the inflammatory biomarkers and lower hormone levels thought to be risk factors for breast cancer in women.

“Overweight or obese women have increased risk for breast cancer in their postmenopausal years,” McTiernan says. “It’s not just weight gain that drives the risk. Overweight/obese postmenopausal women have high blood levels of estrogens, testosterone, inflammatory markers and insulin, all of which can fuel breast cells to proliferate. All evidence suggests that body weight is the key — women don’t get as much benefit from exercise if they are obese as do those who are normal weight.”

The mechanisms behind exercise’s benefit appear to be tied to weight management, according to McTiernan. “We think that exercise reduces risk by lowering estrogen and other hormone levels over one’s lifetime, in large part through reducing body fat,” she said. “Also, inflammation promotes cancer, and individuals with high inflammation markers have increased risk for several cancers. Exercise can reduce some inflammation markers, if weight reduction accompanies the exercise.”

In fact, just a moderate amount of weight loss can significantly reduce the levels of circulating estrogen associated with breast cancer risk, according to a study by McTiernan and her colleagues of 439 overweight-to-obese Seattle-area women aged 50 to 75. The study was published in 2012 in the Journal of Clinical Oncology . McTiernan says diet and exercise together are the best combination. “In the long run that should help keep weight down and therefore keep estrogens down,” she said.

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