A large study published recently in the journal Cancer Epidemiology, Biomarkers, and Prevention found that walking was linked to a lower risk for breast cancer in women who have gone through menopause, and for whom walking was their only form of physical activity in leisure time.
The findings add to a growing pile of evidence linking regular exercise with lower risk for breast cancer.
In their analysis of over 70,000 postmenopausal women, American Cancer Society (ACS) researchers also found that walking was linked to lower breast cancer risk regardless of whether the women were overweight or obese or gained weight during the study period.
In addition, exercise was linked to lower risk for both estrogen receptor positive and estrogen receptor negative cancers.
Nearly half of the women in the study reported walking was their only recreational activity and of these, those who walked 7 or more hours a week had a 14% lower risk of breast cancer, compared with counterparts who only walked 3 hours or less a week.
The women walked at a moderate pace, which is about 3 miles an hour.
The findings also show that women who, as well as walking, did other, more vigorous exercise, had a 25% lower risk of breast cancer, compared with the least active women.
Study leader Dr. Alpa Patel, a senior epidemiologist at the ACS, and strategic director of the society's Cancer Prevention Study-3, says:
"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 1 hour per day was associated with a modestly lower risk of breast cancer. More strenuous and longer activities lowered the risk even more."
The researchers analyzed data on breast cancer and exercise captured in the CPS-II Nutritional Cohort, whose participants included 73,615 postmenopausal women, among whom 4,760 were diagnosed with breast cancer in a 17-year period starting in 1992.
The American Cancer Society recommends adults do at least 150 minutes of moderate-intensity activity or 75 minutes of vigorous intensity activity every week, preferably spread over the week.
Moderate intensity activity is at the level of brisk walking, and vigorous activity challenges the cardiovascular system more, for instance as in running, strong swimming and aerobic dancing.
Dr Patel adds:
"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."
While there is plenty of evidence linking exercise to lower risk for breast cancer, we know little about the underlying biological mechanisms. One idea is that exercise helps regulate hormones like estrogen and insulin, both of which can boost breast cancer growth.
In 2012, a study reported in The Lancet suggested that physical inactivity may cause as many deaths as smoking by contributing to up to 10% of worldwide deaths in four serious non-communicable diseases: coronary heart disease, type 2 diabetes, colon cancer and breast cancer.