Objective: To examine the association between cardiorespiratory fitness (CRF) and the risk of breast cancer in postmenopausal women.
Methods:
This study used data from 17 840 cancer-free postmenopausal women with a CRF assessment from the UK Biobank. High estimated CRF (eCRF) was categorised as being
Results: Over a median follow-up of 11.0 years there were 529 cases of invasive breast cancer, 1623 cases of non-breast cancer disease and 241 deaths. With adjustment for breast cancer risk factors, high eCRF was associated with a 24% (subdistribution HR (SDHR) 0.76, 95% CI 0.60 to 0.97) lower risk of breast cancer. When stratified by measures of body fat, we found evidence of effect measure modification. Mainly, having high eCRF was only associated with a lower risk of breast cancer among those classified as having overweight/obesity (SDHR 0.33, 95% CI 0.11 to 1.01) or percentage body fat above the 1st quintile (SDHR 0.65, 95% CI 0.45 to 0.94).
Conclusion: Having higher CRF may be a protective factor against breast cancer in postmenopausal women but only for women with elevated body fat.
Keywords: Body Mass Index; Body composition; Breast; Physical fitness.
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