(HealthDay News) – For post-menopausal women, increased physical activity is associated with lower levels of estradiol and estrone and with lower levels of specific estrogen metabolites, according to a study presented at the annual meeting of the American Association for Cancer Research, held April 6–10 in Washington, DC.

Noting that previous studies have suggested that physical activity may lower breast cancer risk by reducing endogenous estrogen levels, Cher M. Dallal, PhD, from the National Cancer Institute in Bethesda, MD, and colleagues examined the influence of physical activity on estrogen metabolism. The role of accelerometer-measured physical activity on 15 urinary estrogens and estrogen metabolites was assessed in a cohort of 540 post-menopausal women, aged 40–74 years, not currently taking menopausal hormone therapy.

The researchers found that there was a significant correlation between high activity and lower mean levels of estrone and estradiol. High activity correlated inversely with 2-methoxyestrone, 2-methoxyestradiol, estriol, and 17-epiestriol. There were no other significant correlations for individual estrogen metabolites. In metabolic pathway analysis, women in the highest tertile of activity exhibited significantly increased hydroxylation at the C-2, C-4, and C-16 sites.

“By using these new tools to study the relationship between activity and estrogen metabolism, we hope to get closer to uncovering the combination of parent estrogens, metabolites, and metabolism pathways that are related to a lower-risk profile of breast cancer,” Dallal said in a statement.

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