NEW RESEARCH LOOKS AT ANTI-THYROID EFFECTS OF SOY AND ITS ISOFLAVONES
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One of the world's leading soy researchers, Dr. Daniel Doerge, is lead
author on a research review that was recently published. The study looked at
the evidence in both people and animals that soy has anti-thyroid effects.

There were a number of interesting findings:

*  In animal studies, a diet heavy in soy was able to produce a severe
hypothyroid state characterized by decreased T4, increased TSH and enlarged
thyroid - but only when the animals were also iodine deficient.

*  In other animal studies, only whole soy - but not isoflavones alone -
were sufficient to produce a hypothyroid condition, and again, when the
animals were also iodine deficient

*  Soy-induced goiter, elevated TSH levels, and other hypothyroid indicators
can occur in humans in the absence of iodine deficiency.

*  There is evidence that soy consumption may adversely affect the course of
autoimmune thyroid disease in women.

*  Iodine deficiency is an increasing concern among Americans, because of
reduction in use of iodized salt as a treatment for high blood pressure.
Iodine deficiency may, in conjunction with soy consumption, be a combination
that can produce a hypothyroid condition in humans, and this warrants
further study.

*  Because of the connections between soy isoflavone ability to stimulate
certain immune function, promote formation of antigens, and worsen
autoimmune disease, further study of the use of soy formula in children is
warranted.
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ABSTRACT

Inactivation of thyroid peroxidase by soy isoflavones, in vitro and
in vivo," Doerge D, Chang H., J Chromatogr B Analyt Technol Biomed Life Sci.
2002 Sep 25;777(1-2):269

Division of Biochemical Toxicology, National Center for Toxicological
Research, 3900 NCTR Road, 72079, Jefferson, AR, USA

Soy-containing foods and dietary supplements are widely consumed for
putative health benefits (e.g. cancer chemoprevention, beneficial effects on
serum lipids associated with cardiovascular health, reduction of
osteoporosis, relief of menopausal symptoms). However, studies of soy
isoflavones in experimental animals suggest possible adverse effects as well
(e.g. enhancement of reproductive organ cancer, modulation of endocrine
function, anti-thyroid effects). This paper reviews the evidence in humans
and animals for anti-thyroid effects of soy and its principal isoflavones,
genistein and daidzein.

PMID: 12270219 [PubMed - in process]
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-- Joan McPhee, not an M.D.
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