ISOFLAVONOID LEVELS IN SPOT URINE ARE ASSOCIATED WITH FREQUENCY OF DIETARY SOY INTAKE IN A POPULATION-BASED SAMPLE OF MIDDLE-AGED AND OLDERCHINESE IN SINGAPORE

Soy products contain high amounts of isoflavonoids, which have been sh own to exhibit possible cancer-protective properties. Chinese populati ons in Asia, in particular, have a high level of soy intake and a rela tively low risk of hormone-dependent cancers. In this study, we assess ed the distributions of dietary soy isoflavonoids (daidzein, genistein , and glycitein) and urinary soy isoflavonoids and their metabolites ( daidzein, genistein, glycitein, equol, and O-desmethylangolensin) amon g 147 Singapore Chinese (76 men and 71 women) ages 45-74 years, who ar e participants of the Singapore Cohort Study on diet and cancer. Urina ry values were measured from spot samples collected 10-20 months follo wing recruitment, when usual dietary habits were assessed by a structu red food frequency/portion size questionnaire administered in person. Dietary levels of daidzein and genistein were comparable within indivi duals and about seven times higher than the level of dietary glycitein . All three dietary isoflavonoids showed an approximately 3.5-fold dif ference between the 25th and 75th percentile values. Similarly, daidze in was the most abundant and glycitein the least abundant of the five isoflavonoid compounds in urine. There was a 4.9-fold difference betwe en the 25th and 75th percentile values for the sum of the five urinary isoflavonoids. Among study subjects, there were statistically signifi cant, dose-dependent associations between frequency of overall soy int ake and levels of urinary daidzein (two-sided P = 0.03) and sum of uri nary daidzein, genistein, and glycitein (two-sided P = 0.04). In contr ast, there were no associations between frequency of overall soy intak e and levels of the two daidzein metabolites (equol and O-desmethylang olensin) in urine (two-sided P = 0.85 and 0.34, respectively). We sugg est that within the range of exposures experienced by Singapore Chines e, urinary level of daidzein or the sum of daidzein, genistein, and gl ycitein obtained from a spot sample can serve as a biomarker of curren t soy consumption in epidemiological studies of diet-disease associati ons.