Soybeans might cause a reduction in thyroid hormone production in some people. Thyroid hormones play a key role in the growth and development of all body tissues, bones and the brain, and too little thyroid function, or hypothyroidism, can result in stunted physical and mental growth. Talk to your doctor before adding large amounts of soy to your diet.
Goiter
Soy could be a precipitating factor in goiter development in humans, according to a 1997 study published in the journal "Biochemical Pharmacology." Soy and isoflavones, the estrogen-like compounds contained in soy, might affect both thyroid hormone metabolism and iodine availability. Iodine deficiency is the most common cause of goiter, or a swollen thyroid gland. However, iodine treatment can cure goiter, especially when the treatment begins early.
Refuting Evidence
In 2003, Harvard Medical School researchers investigated the effects of dietary soy isoflavones on the thyroid gland. They randomized 38 healthy, postmenopausal women. Half of the women received a supplement containing 90 mg of total soy isoflavones, while the other half received a placebo. After six months, no difference was observed between the two groups.
Hypothyroidism
Thyroid peroxidase is an enzyme made in the thyroid gland that helps in the absorption of iodine. Your thyroid gland must have iodine to produce thyroid hormones. Studies indicate soy isoflavones cause hypothyroidism through the inhibition of thyroid peroxidase, the Linus Pauling Institute notes.
Soy and Thyroid Medication
Many medications treat hypothyroidism, including thyroid hormone supplements. According to the NYU Langone Medical Center, soy formula might decrease the absorption of anti-thyroid medications in infants, requiring a larger dose of thyroid medicine to offset this effect. A pediatrician should manage any changes in type or dose of medication.
References
- MayoClinic.com; Hypothyroidism (Underactive Thyroid); June 12, 2010
- "The Anti-Estrogenic Diet"; Ori Hofmekler and Rick Osborn; 2007
- Harvard Medical School Health Beat; Do soy products cause thyroid problems?; April 26, 2006
- "Nutrition Noteworthy"; Soy and the Thyroid: Can This Miracle Food Be Unsafe?; Monica Ralli; 2003
- Colorado State University; Synthesis and Secretion of Thyroid Hormones; R. Bowen; March 15, 1999
- Linus Pauling Institute; Soy Isoflavones; Jane Higdon; January 2006
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