Suppression of Thyroid Function during Ingestion of Seaweed "Kombu" (Laminaria japonoca) in Normal Japanese Adults
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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.
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Iodine deficiency causes hypothyroidism while excess iodine uptake can induce either hyper- or hypothyroidism.
“Iodine deficiency causes hypothyroidism while excess iodine uptake can induce either hyper- or hypothyroidism (Miyai et al. 2008).”
From Algae as nutritional and functional food sources: revisiting our understanding. (2017) · cites this paper as Miyai et al. 2008
Thyroid hormones returned to normal levels when seaweed intake ceased.
“Thyroid hormones returned to normal levels when seaweed intake ceased.”
From Algae as nutritional and functional food sources: revisiting our understanding. (2017) · cites this paper as Miyai et al. 2008
There is clear evidence that algal food consumption leads to elevated iodine levels in humans.
“Nevertheless, there is clear evidence that algal food consumption leads to elevated iodine levels in humans.”
From Algae as nutritional and functional food sources: revisiting our understanding. (2017) · cites this paper as Miyai et al. 2008
High levels of iodine in some brown macroalgae (e.g., Laminaria; Saccharina) have led to a strong concern that overconsumption of these particular sea vegetables can be unhealthy.
“In contrast, high levels of iodine in other brown macroalgae (e.g., Laminaria; Saccharina; Teas et al. 2004b; Miyai et al. 2008) have led to a strong concern that overconsumption of these particular sea vegetables can be unhealthy.”
From Algae as nutritional and functional food sources: revisiting our understanding. (2017) · cites this paper as Miyai et al. 2008
The absorbed iodine (20-50 mg) exceeded the recommended upper daily intake of iodine (0.2 mg day−1) by more than an order of magnitude.
“In this case, the absorbed iodine (20–50 mg) exceeded the recommended upper daily intake of iodine (0.2 mg day−1 by more than an order of magnitude; WHO 1989; Dawczynski et al. 2007; Miyai et al. 2008).”
From Algae as nutritional and functional food sources: revisiting our understanding. (2017) · cites this paper as Miyai et al. 2008
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References 23 · Cited by 80
Research works printed but not linked: 2
- Nagataki S (1974) Effect of quantities of iodide. In Geiger SR, Greer MA, Solomon DH et al. (ed) Handbook of Physiology. Sect 7, Vol. 3, Endocri- nology. American Physiological Society, Washington DC: 329-344.
- Ogihara T, Miyai K, KumaharaY, Yamamoto T (1974) A case of hypothyroidism caused by ingestion of the root of Laminaria japonica (Ne-kombu) Japanese Journal of Clinical Medicine (Nippon Rinsho) 32: 2434-2437 (In Japanese).
- Authors
- MIYAI, K., TOKUSHIGE, T., KONDO, M., & Iodine Research Group
- Affiliations
- Koshien University (JP)
- Osaka Kessei Research Laboratories
- Venue
- Endocrine Journal
- Publisher
- Japan Endocrine Society
- Published
- 2008
- Volume
- 55
- Issue
- 6
- Pages
- 1103-1108
- ISSN
- 0918-8959 (ISSN-L)
- 1348-4540
- OpenAlex
- W2022162415
- Cited by
- 80
- References
- 23
- Citations by year
- 2026: 2 · 2025: 4 · 2024: 5 · 2023: 11 · 2022: 7 · 2021: 8 · 2020: 7 · 2019: 7 · 2018: 6 · 2017: 4 · 2016: 4 · 2015: 1 · 2014: 4 · 2013: 5 · 2012: 1
- FWCI
- 0.96
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- Endocrine Journal (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Thyroid Disorders and Treatments
- Life Sciences › Agricultural and Biological Sciences › Aquatic Science › Seaweed-derived Bioactive Compounds
- Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Thyroid Cancer Diagnosis and Treatment
- Keywords
- kombu, Laminaria japonica, seaweed, thyroid function, thyroid suppression, thyroid-stimulating hormone, free thyroxine, free triiodothyronine, urinary iodine excretion, dietary iodine, iodine intake
- MeSH terms
- Adolescent, Adult, Diet, Eating, Female, Humans, Iodine, Japan, Laminaria, Male, Seaweed, Antithyroid Agents, Thyroid Function Tests, Thyroid Gland, Young Adult
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