Soy & Thyroid
Recent work from the University of Minnesota indicates that the consumption of isoflavone-rich soy over a three-month period had little effect on thyroid hormone levels in either pre- or post-menopausal women. And a recent double-blind study involving 38 postmenopausal women over the age of 64 who were not on hormone therapy, found no differences in thyroid function, based on measures of thyroid stimulating hormone (TSH), total thyronine (T4), and triiodothyronine (T3), between women given daily either a placebo or a supplement that provided 90 mg of isoflavones (expressed as aglycone units).
There is no reason to restrict soy consumption over concerns about the impact on thyroid function. When consuming large amounts of soy, it is important to make sure iodine intake is adequate. But of course, all people, regardless of their dietary pattern, need to consume sufficient amounts of iodine. Any concerns about the effect of soy on thyroid levels can be definitively addressed by having thyroid hormone levels measured.
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