(HealthDay News) — In a cohort study of women runners and walkers, less exercise and larger breast cup size were associated with increased mortality from breast cancer, according to research published online Dec. 9 in PLOS ONE.

Paul T. Williams, PhD, of the Lawrence Berkeley National Laboratory in California, followed 79,124 women from the National Walkers’ and Runners’ Health Studies to identify predictors of breast cancer mortality at varying exercise levels.

Williams found that, during 11 years of follow-up, 111 women died from breast cancer. Women, either runners or walkers, who exercised 7.5 metabolic equivalent (MET)-hours/week or more were 41.5% less likely to die from breast cancer than those who exercised less than 7.5 MET-hours/week (hazard ratio [HR] = 0.585). This association persisted even after adjustment for body mass index (BMI) (HR = 0.584).

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The strongest predictor of breast cancer mortality, other than age and menopause status, was baseline bra cup size, with risk increasing by 57.9% per cup size. After adjustment for BMI and other covariates, the risk of breast cancer mortality was significantly greater in women runners or walkers with a C-cup (HR = 3.980) or a D-cup or larger size (HR = 4.668) versus those with an A-cup.

“Breast cancer mortality decreased in association with both meeting the exercise recommendations and smaller breast volume,” Williams writes.


  1. Williams T. Breast Cancer Mortality vs. Exercise and Breast Size in Runners and Walkers. PLoS One. 2013;doi:10.1371/journal.pone.0080616.