Moderate physical activity associated with reduced breast cancer risk

Image: PD/Cancer Cell

1. Moderate physical activity was associated with a 14% reduction in breast cancer risk in postmenopausal women. 

2. Increased sitting time was not associated with risk of breast cancer. 

Evidence Rating Level: 1 (Excellent) 

Study Rundown:  In this large, prospective trial, researchers found that moderate physical activity, such as walking 1 hr/day, was associated with a 14% lower risk of breast cancer in postmenopausal women. More vigorous exercise was associated with a 25% lower risk and increased sitting time was not associated with risk of breast cancer.

The strengths of this study include a prospective design and controlling for numerous confounders (race, BMI, education, alcohol intake, menopausal age, and postmenopausal HRT). Results are limited by self-reporting and homogeneity of the study population (white, middle-aged, and well-educated). Future studies might randomize women (by age since menopause, HRT use, BMI and SES indicator) to differing activity levels to further characterize the association identified here.

Click to read the study in Cancer Epidemiology, Biomarkers & Prevention

Relevant Reading: Up-to-date: Factors that modify breast cancer risk in women

In-Depth [prospective cohort study]: This study included 73,615 postmenopausal women from the American Cancer Society’s Cancer Prevention Study II Nutrition Cohort, who submitted biennial (q2 year) questionnaires. From 1992 to 2009, 4,760 breast cancer cases were identified over a median follow-up of 14.2 years from 1992 to 2009. Activity level and leisure hours spent sitting were categorized.

Among over 70,000 postmenopausal women, 9.2% reported no baseline recreational physical activity and 47% reported walking as their only physical activity. Compared to women who reported the least physical activity, those who reported the most activity were 25% less likely to develop breast cancer (95% CI 0.63-0.89).  Compared to those who reported walking for ≤3 hrs/wk, women who walked for ≥7 hrs/wk were 14% less likely to develop breast cancer (95% CI 0.75-0.98). Increased sitting time was not associated with risk of breast cancer.

By Maren Shapiro and Leah Hawkins, MD, MPH

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