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

Journal of Exposure Science & Environmental Epidemiology volume 19, pages 223–234 (2009)Cite this article

Abstract

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 isoflavone levels in infants. We did a partly cross-sectional and partly longitudinal pilot study to examine children's exposure to isoflavones from different feeding methods. A total of 166 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. A total of 381 urine, 361 saliva, and 88 blood samples were collected at 382 visits. We used automated online solid-phase extraction coupled to high-performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) for measuring three isoflavones (daidzein, genistein, and equol) in urine, and used 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 in the other matrices. Concentrations of equol were detectable only in 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 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.

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Acknowledgements

We are grateful to Zsuzsanna Kuklenyik and John Reidy for the isoflavone measurements in urine and to Liza Valentin-Blasini for helpful discussions.

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Authors and Affiliations

  1. Epidemiology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA

    Yang Cao & Walter J Rogan

  2. Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, Georgia 30341, USA

    Antonia M Calafat & Xiaoyun Ye

  3. Division of Biochemical Toxicology, National Center for Toxicological Research, US Food and Drug Administration, Jefferson, Arkansas 72079, USA

    Daniel R Doerge & Nathan C Twaddle

  4. Biostatistics Branch, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA

    David M Umbach

  5. Department of Pediatrics, Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA

    Judy C Bernbaum

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  1. Yang Cao
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Correspondence to Walter J Rogan.

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Cao, Y., Calafat, A., Doerge, D. et al. Isoflavones in urine, saliva, and blood of infants: data from a pilot study on the estrogenic activity of soy formula. J Expo Sci Environ Epidemiol 19, 223–234 (2009). https://doi.org/10.1038/jes.2008.44

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