Pharmacokinetic and bioavailability information about S-equol is fundamental to understand its absorption and distribution in the body, which also helped to establish the best dosage to use in clinical studies aimed at evaluating the effectiveness of S-equol in hormone-dependent conditions, such as menopause.


The S-equol in supplement tablets is rapidly absorbed from tablets and attains optimal concentrations in the blood stream, providing very high systemic bioavailability when given to healthy postmenopausal women, according to a single-center, open-label, randomized, two-period crossover pharmacokinetic study conducted in white, non-Hispanic women. Bioavailability is a calculation of how much of a given dose of a test compound reaches the blood stream to circulate within the body and have a potential therapeutic effect.

The study also documented that the S-equol supplement offers a means of providing S-equol to those adults that do not produce it after ingestion of soy. The average peak plasma concentration, Cmax, of 10 mg or 30 mg S-equol were 1907┬▒693 or 4953┬▒747 nmol/L, respectively and were both reached one hour after dosing.6


S-equol is rapidly absorbed after oral administration and rapidly excreted in urine, according to a pharmacokinetics evaluation of 12 healthy post-menopausal US women, including equol producers and non-equol producers. The average half-life, the time for plasma concentrations to decrease by 50 percent, was 7 to 8 hours. In the first 12 hours, 75 percent of S-equol was recovered in the urine, but sustained concentrations were measureable through 48 hours after dosing, when after a single dose of S-equol, 82 percent appeared in the urine.6