Frontiers in Endocrinology (Sep 2018)

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

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

DOI
https://doi.org/10.3389/fendo.2018.00531
Journal volume & issue
Vol. 9

Abstract

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Objective: 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.Design and setting: Randomized, double-blind, crossover study.Participants: Forty four patients with subclinical hypothyroidism.Intervention: 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.Main outcome measures: The primary outcome was progression to overt hypothyroidism with the secondary outcome measures were changes in thyroid function tests.Results: Two patients in this trial progressed into overt hypothyroidism after high dose phytoestrogen supplementation. TSH, free thyroxine and triiodothyronine did not differ between groups.Conclusion: 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.

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