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SECOND INTERNATIONAL SYMPOSIUM
ON THE ROLE OF SOY
IN PREVENTING AND TREATING CHRONIC DISEASESeptember 15-18, 1996
Brussells, Belgium
SCIENTIFIC PROGRAM
Satellite Symposium
Current Understanding of Soy and Infant Health
The Developmental Toxicity of Phytoestrogens in Experimental Animals: Are There Concerns For Humans?
Daniel M. Sheehan, Division of Reproductive and Developmental Toxicology, NCTR/FDA, Jefferson, AR 72079.Estrogens have both benefits and risks. Benefits in humans include voluntary infertility (oral contraceptives) and relief of menopausal symptoms (estrogen replacement therapy). Risks were demonstrated for unopposed estrogen replacement therapy (endometrial cancer) and DES exposure (reproductive tract malformations following fetal exposure). Concern has been expressed regarding risks from unintended exposures to a variety of environmental estrogens; the highest level of concern is for developmental exposures leading to impaired reproductive function. This is due to great sensitivity (a brief exposure during critical periods of organ development is effective) and irreversibility (the organ systems do not subsequently revert to normal) which is expressed as population losses.
Phytoestrogens are prototypical environmental estrogens known to induce infertility in livestock fed phytoestrogen-containing forage. Human exposure during development occurs primarily through phytoestrogen-rich soy infant formula. In experimental animals, some phytoestrogens cause abnormal development of female reproductive tract tissues, including the uterus (inhibition of uterine gland differentiation) and ovary (polyovular follicles, altered follicle development), as well as having actions on the developing brain (causing infertility due to neural failure to regulate estrus cycles). These data, taken together, suggest that it is important to define the degree of hazard, if any, caused by human, livestock or wildlife exposure to phytoestrogens so that potential risks and potential benefits, and the conditions under which they occur, can be defined.
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