Isoflavones in urine saliva and blood of infants – data from a pilot study on the estrogenic activity of soy formula

摘要

In the United States, about 25% of infant formula sold is based on soy protein, which is an important source of estrogenic isoflavones in the human food supply. Nevertheless, few studies report isoflavones levels in infants. We did a partly cross-sectional, partly longitudinal pilot study to examine children’s exposure to isoflavones from different feeding methods. One hundred sixty-six full term infants between birth and 1 year of age were recruited into soy formula, cow milk formula or breast milk regimens according to their feeding histories. Three hundred eighty-one urine, 361 saliva and 88 blood samples were collected at 382 visits. We used automated online SPE coupled to HPLC-MS/MS for measuring three isoflavones (daidzein, genistein, and equol) in urine, and use similar LC/MS/MS techniques for saliva and blood spots . Concentrations of daidzein and genistein were undetectable in most blood or saliva samples from children fed breast milk or cow-milk formula. The proportion of non-detectable values was somewhat lower in urine than the other matrices. Concentrations of equol were detectable in only a few urine samples. For both daidzein and genistein, urine contained the highest median concentrations, followed by blood, and then saliva. Urinary concentrations of genistein and daidzein were about 500 times higher in the soy-formula-fed infants than in the cow-milk-formula-fed infants. The correlations between matrices for either analyte were strikingly lower than the correlation between the two analytes in any single matrix. We did not find significant correlations between isoflavone concentrations and the levels of certain hormones in children fed soy formula. Our results, based on much larger numbers of infants, strongly confirm previous reports, but whether the phytoestrogens in soy formula are biologically active in infants is still an open question. We plan further longitudinal studies focusing on physical and developmental findings reflecting the effects of estrogen exposure.