Is Soy Beneficial to Thyroid Function?

Disclaimer: Results are not guaranteed*** and may vary from person to person***.

— by Jeff Jurmain, MA

Early last decade, concern started to build that soy may cause harmful interactions in a postmenopausal woman’s body. The “isoflavones” in soy, special plant chemicals, were tied to hormonal effects. But now this concern has been tempered a bit and soy is not making the news much in this regard.

In the meantime, researchers have been performing studies to assess the true relationship between soy and menopause. One of them, just published, found that “genistein,” a supplement derived from soy, doesn’t appear to harm a woman’s thyroid function.

Genistein is one of those famous isoflavones and its makeup is similar to the hormone estrogen. Genistein is believed to mimic estrogen in the body, which could have positive and negative results. One positive study from 2007 found that these supplements (with calcium and vitamin D) could strengthen bones in postmenopausal women whose bones are thinning.

It is this same clinical trial that was assessed by the new group of researchers. But rather than bones, they wanted to see if genistein affected the thyroid. Thyroid is a gland in the body that has direct influence on many bodily processes, including metabolism. If the thyroid is underactive, it can pave the road to health issues such as weight gain, chronic fatigue, and sensitivity to cold.

Previous research has indicated that isoflavones could lower the amount of thyroid hormones being produced. It has also found that isoflavones could be disrupting the essential mineral iodine, which your body needs to build such hormones.

But here’s the rub: those studies used doses of genistein that were much, much higher than those levels used in the new study — and those levels generally taken by people in supplements. The new study used 54 milligrams a day among a group of participants who were followed for three years. The women taking genistein supplements showed no difference in thyroid function than women taking a placebo.

So it seems that, yes, taking very high doses of genistein could have damaging thyroid effects. But taking smaller doses or obtaining isoflavones from soy foods (such as tofu) is not likely to disrupt the thyroid function. While the safety of soy still needs to be studied more, this is positive news for postmenopausal women looking for natural sources of estrogen or those who enjoy eating soy products.

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