The Effects of Physical Exercise on Selected Markers of Estrogen Metabolism Linked to Breast Cancer Risk in Premenopausal Women

Background: Physical activity is linked to breast cancer risk reduction in women, yet the mechanism remains largely unknown. Possible causes for this association have been hypothesized to include change in endogenous estrogen production, estrogen metabolism, circulating concentrations of peptide hormones and growth factors, obesity, central adiposity, and immune function. Recent investigations in estrogen metabolism in women have brought to light a new possibility for the association between physical activity and breast cancer risk to be related to 2-hydroxyestrone metabolism increases with exercise, relative to 16α-hydroxyestrone. This metabolite pathway has been studied as a mechanism for postmenopausal breast cancer risk, but there are few studies concerning eumenorrheic, premenopausal women. The purpose of this systematic review is to evaluate the most current research on this topic. Methods: An exhaustive search of available medical literature concerning estrogen metabolism, breast cancer risk, physical activity, and premenopausal females was conducted. The reviewed studies were limited to randomized controlled trials, and prospective and retrospective cohort investigations. Results: The six articles included in this review showed either non-significant changes in estrogen metabolism to favor the anti-estrogenic 2-hydroxyestrone pathway, or no change at all in estrogen metabolism as a result of physical activity. The only investigation reaching statistically significant results was a retrospective cohort study relying on self-reports of physical activity. The six studies reviewed demonstrate vastly different inclusion and exclusion criteria, as well as intervention protocols, causing comparison between studies to be imprecise. Conclusion: Current research has yet to identify the cause of the association between physical activity and reduced breast cancer risk as related to changes in estrogen metabolism. Further investigation with large randomized controlled trials with objectively measuring physical activity, utilizing standardized methods of gathering and analyzing data is needed