AUTHOR=Sathyapalan Thozhukat , Dawson Alison J. , Rigby Alan S. , Thatcher Natalie J. , Kilpatrick Eric S. , Atkin Stephen L. 

TITLE=The Effect of Phytoestrogen on Thyroid in Subclinical Hypothyroidism: Randomized, Double Blind, Crossover Study

JOURNAL=Frontiers in Endocrinology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/endocrinology/articles/10.3389/fendo.2018.00531

DOI=10.3389/fendo.2018.00531

ISSN=1664-2392

ABSTRACT=<p><bold>Objective:</bold> Soy phytoestrogens are suggested to impair thyroid function but the effects of pharmacological doses of soy phytoestrogens are unknown; therefore, this study was performed to determine the effect of high dose soy phytoestrogens (66 mg) on thyroid function in subclinical hypothyroidism.</p><p><bold>Design and setting:</bold> Randomized, double-blind, crossover study.</p><p><bold>Participants:</bold> Forty four patients with subclinical hypothyroidism.</p><p><bold>Intervention:</bold> Participants were randomly allocated to either 66 mg phytoestrogen with 30 g soy protein (active) or 0 mg phytoestrogen with 30 g soy protein (placebo) supplementation for 8 weeks, washed out for 8 weeks and then crossed over for another 8 week period.</p><p><bold>Main outcome measures:</bold> The primary outcome was progression to overt hypothyroidism with the secondary outcome measures were changes in thyroid function tests.</p><p><bold>Results:</bold> Two patients in this trial progressed into overt hypothyroidism after high dose phytoestrogen supplementation. TSH, free thyroxine and triiodothyronine did not differ between groups.</p><p><bold>Conclusion:</bold> A pharmacological dose of 66 mg of soy phytoestrogens did not increase the overt thyroid failure rate or alter thyroid function tests in patients with subclinical hypothyroidism.</p>