Are sea vegetables a good source of iodine?

No food group serves as a better iodine source than sea vegetables. According to the Institute of Medicine at the National Academy of Sciences, adults need 150 mcg (micrograms) of iodine each day to meet their health needs. Depending upon the specific type of sea vegetable, this guideline can be met by 1-2 grams of sea vegetableóthe amount contained in about to 2/3 - 1 teaspoon.

Kelps, including bladderwrack (Fucus vesiculosus), usually contain between 100-200 micrograms of iodine per gram (meeting daily iodine needs with a serving of about 2/3 - 1 teaspoon). Kelps are particularly interesting with respect to iodine because some studies suggest that between 5-35% of the iodine contained in some varieties of kelp is actually stored in the same forms in which iodine is found in our thyroid hormones. In these organic forms, iodine is hooked together with the amino acid tyrosine. Tyrosine connected with one iodine atom (mono-iodotyrosine), two iodine atoms (di-iodo-tyrosine) and three iodine atoms (tri-iodo-tyrosine) appears to be found within some kelps. These iodine-tyrosine combinations are primary constituents of our thyroid hormones, T3 (which contains 3 iodine atoms) and T4 (which contains 4 iodine atoms). In keeping with these observations, some research has also suggested lower rates of thyroid-related problems in countries where sea vegetables are consumed regularly.

Compared to ordinary table salt, sea vegetables have a slightly higher iodine content. A gram of iodized table salt typically contains about 65 micrograms of iodine. For sea vegetables, the range is 79-300 micrograms (see table below).

Sea Vegetable Amount Iodine Content
kelps 1 gram 100-200 micrograms
wakame 1 gram 79 micrograms
dulse 1 gram 150-300 micrograms
Compared with
iodized table salt 1 gram 65 micrograms

It is important to note that sea vegetables vary greatly in their iodine content, depending on the circumstances in which they grow. Even state-of-the-art databases, like Food Processor for Windows Database Version 7.60, ESHA Research, Salem, Oregon, do not provide iodine values for sea vegetables.

The reason is simple: the iodine content of most sea vegetables is just too variable.

Variations in sea vegetablesí iodine content are due to two factors. First, the iodine content of marine water undergoes much greater natural change than the iodine content of soil. And secondly, unlike other minerals, which usually get hooked onto other substances in sea vegetables, iodine does not hook onto other substances very readily but tends to stay in its free, water-soluble form. In studies of Pacific sea vegetables, for example, about 10% of the total iodine content is hooked onto other substances (usually parts of protein, called amino acids) while the other 90% remains in its free, water-soluble form. Since most of the iodine remains water-soluble, even when itís inside the sea vegetable, it can easily move back and forth between the ocean and the plant. This constant movement of iodine in its water-soluble form means that some sea vegetables can increase or decrease their iodine content by as much as 10-fold depending on ocean conditions. For this reason, itís best to think of sea vegetables as providing a high amount of iodine that falls within a general range, rather than a specific, pinpoint amount.

References:

Arasaki, S. & Arasaki, T. (1983). Vegetables from the sea. Japan Publ. Inc.Tokyo.

Haug, A. & Jensen, A. (1954). Seasonal variations in the chemical composition of Alaria esculenta, Laminaria saccharina, Laminaria hyperborea and Laminaria digitata from northern Norway. Rep. Norw. Inst. Of Seaweed Res. No 4. Trondheim: Institutt for bioteknologi, NTH.

This page was updated on: 2004-11-18 18:11:20
© 2002 The George Mateljan Foundation