Kelp is a sea vegetable that is a concentrated source of minerals, including iodine, potassium, magnesium, calcium, and iron. Kelp as a source of iodine assists in making thyroid hormones, which are necessary for maintaining normal metabolism in all cells of the body.

How It Works

How to Use It

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

Where to Find It

Kelp can be one of several brown-colored seaweed species called Laminaria.

Possible Deficiencies

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.


Interactions with Supplements, Foods, & Other Compounds

At the time of writing, there were no well-known supplement or food interactions with this supplement.

Interactions with Medicines

As of the last update, we found no reported interactions between this supplement and medicines. It is possible that unknown interactions exist. If you take medication, always discuss the potential risks and benefits of adding a new supplement with your doctor or pharmacist.
The Drug-Nutrient Interactions table may not include every possible interaction. Taking medicines with meals, on an empty stomach, or with alcohol may influence their effects. For details, refer to the manufacturers’ package information as these are not covered in this table. If you take medications, always discuss the potential risks and benefits of adding a supplement with your doctor or pharmacist.

Side Effects

Side Effects

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.