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The effect of physical activity on breast cancer risk may be partly mediated by sex steroid hormones. This review synthesised and appraised the evidence for an effect of physical activity on sex steroid hormones. Systematic searches were performed using MEDLINE (Ovid), EMBASE (Ovid), and SPORTDiscus to identify experimental studies and prospective cohort studies that examined physical activity and estrogens, progestins, and/or androgens, as well as sex hormone binding globulin (SHBG) and glucocorticoids in pre- and post-menopausal women. Meta-analyses were performed to generate effect estimates. Risk of bias was assessed, and the GRADE system was used to appraise quality of the evidence. Twenty-eight randomized controlled trials (RCTs), 81 non-randomized interventions, and six observational studies were included. Estrogens, progesterone, and androgens mostly decreased, and SHBG increased, in response to physical activity. Effect sizes were small, and evidence quality was graded moderate or high for each outcome. Reductions in select sex steroid hormones following exercise supports the biological plausibility of the first part of the physical activity – sex hormone – breast cancer pathway. The confirmed effect of physical activity on decreasing circulating sex steroid hormones supports its causal role in preventing breast cancer.
Bibliographical noteFunding Information:
Funding (IIG_2018_1732) was obtained from Wereld Kanker Onderzoek Fonds (WKOF), as part of the World Cancer Research Fund International grant programme. B.M. Lynch was supported by the Victorian Cancer Agency (MCRF18005). K.A. Brown is supported by NIH/NCI R01 CA215797. R.M. Martin was supported by the NIHR Biomedical Research Centre at University Hospitals Bristol and Weston NHS Foundation Trust and the University of Bristol. R.M. Martin was supported by a Cancer Research UK (C18281/A29019) programme grant (the Integrative Cancer Epidemiology Programme).
C.T.V. Swain reports grants from World Cancer Research Fund during the conduct of the study. L. Boing reports grants from Coordenac¸ão de Aperfeic¸oamento de Pessoal de Nível Superior - Brasil (CAPES) during the conduct of the study. R.L. Milne reports grants from World Cancer Research Fund during the conduct of the study. D.R. English reports grants from World Cancer Research Fund during the conduct of the study. K.A. Brown reports grants from World Cancer Research Fund (funded by Wereld Kanker Onderzoek Fonds) and NIH/NCI R01CA215797 during the conduct of the study. E.H. van Roekel reports grants from Wereld Kanker Onderzoek Fonds (WKOF), as part of the World Cancer Research Fund International grant programme (Grant No. 2016/1620) during the conduct of the study. T.R. Gaunt
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- breast neoplasm
- gonadal steroid hormones
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