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Prenatal Exposure to Soy Isoflavones and Anogenital Distance in Male Newborns

Suzuki, Yayoi1; Yoshinaga, Jun1; Mizumoto, Yoshifumi2; Serizawa, Shigeko3; Shiraishi, Hiroaki3

doi: 10.1097/01.ede.0000392173.71759.db
Abstracts: ISEE 22nd Annual Conference, Seoul, Korea, 28 August–1 September 2010: Environmental Health Effects on Susceptible Populations

1Department of Environmental Studies, The University of Tokyo, Chiba, Japan; 2Department of Obstetrics and Gynecology, Central Hospital of Self-Defense Force, Tokyo, Japan; and 3National Institute for Environmental Studies, Tsukuba, Japan.

Abstracts published in Epidemiology have been reviewed by the societies at whose meetings the abstracts have been accepted for presentation. These abstracts have not undergone review by the Editorial Board of Epidemiology.


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Soy products are traditionally consumed among many Asian countries, including susceptible population such as pregnant women and infants, in their daily life. This has raised concerns over the health effects to fetuses and infants by soy isoflavones that has estrogenic activity. Fetal exposure to soy isoflavones disrupts reproductive development in animals. However, there are few studies that examined the potential effect in humans. The purpose of the present study was to assess relationship between fetal exposure to daidzein, and its metabolite, equol, and reproductive endpoint of male newborns.

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Spot urine samples were collected from 101 Japanese pregnant women after obtaining informed consent. The urinary concentrations were measured by gas chromatography-mass spectrometry (GC-MS) after solid phase extraction of urine samples and derivatization. For the male newborns, birth outcomes and anogenital distance (AGD), the distance from the center of the anus and external genitalia, were measured. AGI (mm/kg bw) was defined as AGD corrected by birth weight.

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The median urinary concentrations were 1.42 and 0.137 mg/g cre for daidzein and equol, respectively. The levels were comparable to the reported values in Japan but higher than those of female subjects in the United States by 20 times. Equol was detected in 58% of the subjects. Mean AGI was 14.7 mm/kg and normally distributed. In multiple regression analysis, there was no association between urinary daidzein or equol concentration and AGI of male newborns (standardized partial regression coefficient (β) = 0.157, P = 0.115 for daidzein; β = −0.130, P = 0.224 for equol).

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We found no association between prenatal exposure to daidzein and equol and anogenital distance of male newborns in Japan. However, since estrogenic isoflavone exposure level is much higher in Japanese fetus than in other populations, we may need to carefully examine its potential effects.

© 2011 Lippincott Williams & Wilkins, Inc.