As more and more postmenopausal women are taking soy isoflavone supplementation for relieving menopausal symptoms, we investigated the impact of chronic exposure on their bioavailability, with focus on achievable plasma concentrations and potential stimulation of the capacity to produce equol.
A total of 12 Caucasian postmenopausal women.
Volunteers ingested 100 mg isoflavones/day (aglycone equivalents, in cereal bars and yoghurts) for 1 month. Plasma concentrations of metabolites at 2, 4, 6, 8, 10, 12 and 24 h postdose, as well as urinary excretion in fractions over 36 h were compared between days 1 and 30.
Similar plasma kinetic curves were obtained at day 1 and day 30 for genistein and daidzein. Maximum plasma concentrations were 1.68±0.68 μmol/l on day 1 compared to 2.27±0.76 μmol/l on day 30 for daidzein (P=0.056), and 3.88±1.50 μmol/l on day 1 compared to 5.30±2.38 μmol/l on day 30 for genistein (P=0.091). Urinary excretion of daidzein and genistein did not differ significantly between days 1 and 30. Maximum plasma concentration of equol increased significantly from 0.31±0.27 to 0.99±0.51 μmol/l for equol-producer volunteers (P=0.046). However, the seven volunteers who were classified as non-equol producers on day 1 did not acquire the ability to produce equol after 1-month exposure.
Chronic exposure to isoflavones in postmenopausal women resulted in plasma concentrations as high as 2.5–5 μmol/l of each isoflavone, but did not induce the ability to produce equol.
French Ministry of Research (AQS program A01347) and Beghin-Meiji (doctoral fellowship).
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This work was supported in part by the French Ministry of Research (AQS program A01347) and Beghin-Meiji (doctoral fellowship). We are grateful to Eridania Beghin-Say and Beghin-Meiji for kindly supplying the powdered isoflavone concentrate (Prevastein ®HC).
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Védrine, N., Mathey, J., Morand, C. et al. One-month exposure to soy isoflavones did not induce the ability to produce equol in postmenopausal women. Eur J Clin Nutr 60, 1039–1045 (2006). https://doi.org/10.1038/sj.ejcn.1602415
- chronic exposure
- dietary supplements
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