Distribution of 24-h urinary equol excretion as an indicator of the physiological range in healthy Japanese equol excretors

Equol is produced from daidzein, a soy isoflavone, through metabolism by intestinal bacteria, and benefits health. This cross-sectional study aimed to investigate its physiological range, using 24 h urinary equol excretion as an indicator, in Japanese people who consume soybeans in their usual diet. The 24 h urine of 1345 subjects (545 men and 800 women) was collected, and equol, daidzein, and genistein concentrations were measured. Subjects with detectable equol in their urine (⩾0.27 nmol/ml) were considered equol excretors. Among men, 36.3% were equol excretors; among women, 40.8%. The rate of equol excretors and urinary equol excretion differed significantly by age, but not by gender. In all equol excretors, the range of 24 h urinary equol excretion was 0.4-318.0 μmol/day; the median was 12.5 μmol/day; and the 95th percentile was 119.2 μmol/day. This range appears to be the physiological range of equol excretion in Japanese people who consume soy food regularly.