Since the introduction of iodized salt, additional sources of iodine, such as kelp, are not necessary for most people. However, kelp can be consumed as a source of other minerals. A report from Great Britain indicated that the average kelp-based supplement contained 1,000 mcg of iodine (the adult RDA in the United States is 150 mcg per day). It has been suggested that intakes above 2,000 mcg per day should be regarded as excessive or potentially harmful.1
Kelp can be one of several brown-colored seaweed species called Laminaria.
People who avoid sea vegetables, as well as dairy, seafood, processed food, and the salt shaker, can become deficient in iodine. Iodine deficiency can cause low thyroid function, goiter, and cretinism. Although iodine deficiency is now uncommon in Western societies, the U.S. population has shown a trend of significantly decreasing iodine intake.
There have been several case reports of high intakes of kelp providing too much iodine and interfering with normal thyroid function.2 , 3 , 4 , 5 , 6 People with thyroid disease should check with a doctor before taking supplements that contain kelp.
1. Wolff J. Iodide goiter and the pharmacologic effects of excess iodide. Am J Med 1969;47:101–24.
2. Shilo S, Hirsch HJ. Iodine-induced hyperthyroidism in a patient with a normal thyroid gland. Postgrad Med J 1986;62:661–2.
3. Ishizuki Y, Yamauchi K, Miura Y. [Transient thyrotoxicosis induced by Japanese kombu]. Nippon Naibunpi Gakkai Zasshi 1989;65:91–8 [in Japanese].
4. Hartman AA. [Hyperthyroidism during administration of kelp tablets (letter)]. Ned Tijdschr Geneeskd 1990;134:1373 [in Dutch].
5. de Smet PA, Stricker BH, Wilderink F, Wiersinga WM. [Hyperthyroidism during treatment with kelp tablets]. Ned Tijdschr Geneeskd 1990;134:1058–9 [in Dutch].
6. Eliason BC. Transient hyperthyroidism in a patient taking dietary supplements containing kelp. J Am Board Fam Pract 1998;11:478–80.
Last Review: 05-01-2013
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