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9854695 
Journal Article 
Suppression of thyroid function during ingestion of seaweed "Kombu" (Laminaria japonoca) in normal Japanese adults 
Miyai, K; Tokushige, T; Kondo, M; Iodine Research Group 
2008 
Yes 
Endocrine Journal
ISSN: 0918-8959 
55 
6 
1103-1108 
English 
18689954 
The effect of ingesting seaweed "Kombu" (Laminaria japonica) on thyroid function was studied in normal Japanese adults. Ingesting 15 and 30 g of Kombu (iodine contents: 35 and 70 mg) daily for a short term (7-10 days) significantly increased serum thyrotropin (TSH) concentrations, exceeding the normal limits in some subjects. The serum free thyroxine (FT(4)) and/or free 3,5,3'-triiodothyronine (FT(3)) concentrations were slightly decreased within the normal limits. During long term daily ingestion of 15 g of Kombu (55-87 days), the TSH levels were elevated and sustained while the FT(4) and FT(3) levels were almost unchanged. Urinary excretion of iodine significantly increased during ingestion of Kombu. These abnormal values returned to the initial levels 7 to 40 days after discontinuing the ingestion of Kombu. Based on these findings that thyroid function was suppressed during ingestion of Kombu, though the effect was reversible, we recommend Japanese people avoid ingesting excessive amounts of seaweed.