Seaweed and soy: Companion foods in Asian cuisine and their effects on thyroid function in American women

Jane Teas, Lewis E. Braverman, Mindy S. Kurzer, Sam Pino, Thomas G. Hurley, James R. Hebert

Research output: Contribution to journalArticlepeer-review

59 Scopus citations


Seaweeds and soy are two commonly eaten foods in Asia. Both have been reported to affect thyroid function, seaweed because of its iodine content and soy because of its goitrogenic effect. Twenty-five healthy postmenopausal women (mean age 58 years) completed a double-blinded randomized crossover study. Ten capsules (5 g/day) of placebo or seaweed (Alaria esculenta), providing 475 μg of iodine/day, were consumed daily for 7 weeks. A powdered soy protein isolate (Solae Co., St. Louis, MO), providing 2 mg of isoflavones/kg of body weight, was given daily during the last week of each treatment arm. On average, this provided 141.3 mg of isoflavones/day and 67.5 g of protein/day. Blood samples and 48-hour urine samples were collected before and after each intervention period, and urinary I/C (μg of iodine/g of creatinine) and serum thyroxine, free thyroxine index, total triiodothyronine, and thyroid stimulating hormone (TSH) were measured. Seaweed ingestion increased I/C concentrations (P < .0001) and serum TSH (P < .0001) (1.69 ± 0.22 vs. 2.19 ± 0.22 μU/mL, mean ± SE). Soy supplementation did not affect thyroid end points. Seven weeks of 5 g/day seaweed supplementation was associated with a small but statistically significant increase in TSH. Soy protein isolate supplementation was not associated with changes in serum thyroid hormone concentrations.

Original languageEnglish (US)
Pages (from-to)90-100
Number of pages11
JournalJournal of Medicinal Food
Issue number1
StatePublished - Mar 2007


  • Breast cancer
  • Chemoprevention
  • Diet
  • Postmenopausal women
  • Seaweed
  • Soy
  • Thyroid stimulating hormone


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