Body fat percentage, physical activity and breast cancer risk in 126,000 postmenopausal women in UK Biobank
Body size and physical activity are two important modifiable factors for breast cancer. Obesity has been associated with increased risk for postmenopausal breast cancer. However, previous studies generally used body mass index (BMI) which, unlike body fat percentage, is unable to distinguish between fat and lean mass. We investigate the associations between body fat percentage, physical activity, and postmenopausal breast cancer. We also examined whether the association between physical activity and breast cancer risk remained significant after adjusting for body fat percentage.
Within the UK Biobank cohort, multivariable-adjusted Cox proportional hazards models were used to examine relationships between body fat percentage, vigorous physical activity, and breast cancer risk. We analyzed data from 125,788 postmenopausal women followed from 2006 through 2011. We observed 1,122 incident invasive breast cancers during a mean 2.9 years of follow-up.
Compared with women in the lowest quartile of body fat percentage [mean, 28.6; standard deviation (SD), 3.7], women in the highest quartile (mean, 45.4; SD, 2.9), had an increased risk of breast cancer (HR, 1.47; 95% confidence interval (CI), 1.23-1.76). Women who participated in the most vigorous physical activity had a lower risk of breast cancer than the least active women (HR, 0.82; CI, 0.70-0.96). The inverse association between breast cancer risk and higher levels of vigorous physical activity was slightly attenuated after adjusting for body fat percentage (HR, 0.85; CI, 0.73-1.00).
Our results show that women with a high percentage of body fat have a high risk for breast cancer, and suggest that vigorous physical activity protects against breast cancer, beyond its role in decreasing body fat percentage.
We would like to gratefully acknowledge Theo Giannopoulos and Susanne Booth at Castle Hill Hospital for their help in acquiring ovarian tissue samples, and Jane Smales for coordinating the clinical aspects of the study. This study is funded by a grant from NC3Rs (Registry File: G1100600).
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