title: Urinary equol excretion in relation to 2-hydroxyestrone and 16alpha-hydroxyestrone concentrations: an observational study of young to middle-aged women.
abstract: Approximately one-third to one-half of individuals harbor the colonic bacteria that are capable of metabolizing the soy isoflavone daidzein to equol. Results of prior studies suggest beneficial effects of producing equol in relation to breast cancer risk, potentially through effects on endogenous hormones. High urinary excretion of 2-hydroxyestrone (2-OH E(1)) relative to 16alpha-hydroxyestrone (16alpha-OH E(1)) has been associated with a reduced risk of breast cancer. In this pilot study we examined associations between urinary excretion of equol and 2-OH E(1), 16alpha-OH E(1), and their ratio, and investigated whether excretion of these estrogen metabolites differed between two samples collected 48h apart. Isoflavones (genistein, daidzein, O-desmethylangolensin (ODMA), and equol) were measured in two overnight urines from 126 women. Excretion of 2-OH E(1) and 16alpha-OH E(1) were measured in the first overnight urine from all 126 women and in the second overnight urine from 30 of these women; there were no significant differences between samples collected 48h apart in excretion of 2-OH E(1) or 16alpha-OH E(1) (P=0.75 and 0.17, respectively). Among all women, correlations between total isoflavone excretion (sum of genistein, daidzein, ODMA, and equol) and estrogen metabolites were non-significant (P>0.05). Among women with detectable levels of equol, total isoflavone excretion was significantly positively correlated with 16alpha-OH E(1) (r=0.32, P=0.02), but was not correlated with 2-OH E(1) or 2-OH E(1):16alpha-OH E(1) ratio (r=0.21, P=0.14, and r=-0.05, P=0.70, respectively). Equol excretion (adjusted for other isoflavone excretion) was significantly positively correlated with 2-OH E(1):16alpha-OH E(1) ratio (r=0.38, P=0.005), but was not correlated with 2-OH E(1) or 16alpha-OH E(1) (r=0.15, P=0.29, and r=-0.17, P=0.24, respectively). The finding that equol excretion, but not total isoflavone excretion, correlated positively with the 2-OH E(1):16alpha-OH E(1) ratio suggests that the colonic bacterial profile associated with equol production may be involved in estrogen metabolism, and may therefore possibly influence breast cancer risk.
authors.affiliation: Cancer Prevention Research Program, Fred Hutchinson Cancer Research Center, P.O. Box 19024, MP-900, Seattle, WA 98109-1024, USA.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Atkinson
authors.forename: Heather E
authors.initials: HE
authors.lastname: Skor
authors.forename: E
authors.initials: E
authors.lastname: Dawn Fitzgibbons
authors.forename: Delia
authors.initials: D
authors.lastname: Scholes
authors.forename: Chu
authors.initials: C
authors.lastname: Chen
authors.forename: Kristiina
authors.initials: K
authors.lastname: Wähälä
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Schwartz
authors.forename: Johanna W
authors.initials: JW
authors.lastname: Lampe
mesh_terms: D000328:Adult; D002839:Chromans / Q000652:urine*; D060754:Equol; D005260:Female; D006801:Humans; D006894:Hydroxyestrones / Q000652:urine*; D007529:Isoflavones / Q000652:urine; D008875:Middle Aged; D010865:Pilot Projects; D015203:Reproducibility of Results; D013997:Time Factors
chemical_list: C007610:4',7-dihydroxy-3,4-dihydroisoflavone; D002839:Chromans; D006894:Hydroxyestrones; D007529:Isoflavones; D060754:Equol