Soy: thyroid problems a flash in the pan

Soy: thyroid problems a flash in the pan

By Benjamin Brown N.D

 

A recent 3 year safety study has found that the soy isoflavone genistein does not affect thyroid function adding to a growing body of evidence that dismisses previous concerns about soy and thyroid health.

 

Soy foods and supplements have been shown to be useful for improving hot flashes in postmenopausal women yet there are still concerns around effects on thyroid gland function. In a safety investigation a group of postmenopausal women receiving 54 mg of the soy isoflavone genistein were assessed for thyroid function after three years of treatment.

 

Circulating thyroid hormones (TSH, free T(3), free T(4)) and autoantibodies (thyroid peroxidase, thyroglobulin, and thyroid microsomal antigen) were assessed after the three years of treatment and did not differ from women receiving placebo. This report suggests that genistein at a dose of 54 mg per day over three years has no effect on the development of clinical or subclinical thyroid disease.

 

Comment:

Early concerns about the safety of soy for thyroid health came from experimental studies however the largest review of the hormonal effects of soy to date found no evidence of an effect of soy protein or soy isoflavones on thyroid hormones in women. The review and meta-analysis (Hum Reprod Update. 2009 Jul-Aug;15(4):423-40.) included some 47 published human clinical studies.

 

This recent study adds to evidence in support of the safety of soy and thyroid health. Good for hot flashes and not harmful for the thyroid it seems.

 

Source:

Bitto A, et al. Genistein aglycone does not affect thyroid function: results from a three-year, randomized, double-blind, placebo-controlled trial. J Clin Endocrinol Metab. 2010 Jun;95(6):3067-72.