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Related Experiment Videos

Isoflavone supplements do not affect thyroid function in iodine-replete postmenopausal women.

Bonnie Bruce1, Mark Messina, Gene A Spiller

  • 1Division of Immunology and Rheumatology, Department of Medicine, Stanford University, Palo Alto, CA 94304, USA. bbruce@stanford.edu

Journal of Medicinal Food
|February 24, 2004
PubMed
Summary

Concerns about soy isoflavones affecting thyroid function persist, but this study found no adverse effects in healthy postmenopausal women. Soy isoflavone supplements did not impact thyroid-stimulating hormone, thyroxine, or triiodothyronine levels.

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Area of Science:

  • Endocrinology
  • Nutritional Science
  • Public Health

Background:

  • Soy protein has an FDA-approved health claim for cholesterol-lowering.
  • Concerns exist regarding potential goitrogenic effects of soybean isoflavones.
  • These concerns stem from in vitro, animal studies, and historical infant cases.

Purpose of the Study:

  • To investigate the effect of daily soy isoflavone supplementation on thyroid function in postmenopausal women.
  • To determine if soy isoflavones adversely impact thyroid hormone levels in iodine-replete individuals.

Main Methods:

  • A randomized, double-blind, placebo-controlled study was conducted.
  • 38 postmenopausal women (64-83 years) received 90 mg of total isoflavones or a placebo daily.
  • Thyroid-stimulating hormone (TSH), thyroxine (T4), and triiodothyronine (T3) were measured at baseline and after 90 and 180 days.

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Main Results:

  • No statistically significant differences in TSH, T4, or T3 levels were observed between the isoflavone and placebo groups at any measurement point.
  • Intragroup differences in thyroid hormone levels within both the supplement and control groups were also statistically indistinguishable at 6 months.
  • Thyroid function remained stable in both groups throughout the 180-day study period.

Conclusions:

  • Daily soy isoflavone supplementation does not adversely affect thyroid function in healthy, iodine-replete postmenopausal women.
  • The study provides evidence against the goitrogenic concerns associated with soy isoflavones in this population.
  • Findings suggest that soy isoflavones can be safely consumed without negatively impacting thyroid health.