Iodine is needed for healthy thyroid function which regulates metabolism. Both too much, and too little, iodine can result in abnormal thyroid metabolism. The UK Vegan Society provides an overview on idoine deficiency. An excerpt:
- …Iodine deficiency during pregnancy and early infancy can result in cretinism (irreversible mental retardation and severe motor impairments)…. Hypothyroidism can manifest as low energy levels, dry or scaly or yellowish skin, tingling and numbness in extremities, weight gain, forgetfulness, personality changes, depression, anaemia, and prolonged and heavy periods in women…. Hypothyroidism can also cause carpal tunnel syndrome and Raynaud’s phenomenon [
- ]. Hypothyroidism can lead to significant increases in cholesterol levels and homocysteine levels and is implicated in about 10% of cases of high cholesterol levels. Correcting hypothyroidism can lead to a 30% drop in cholesterol and
Studies have shown that vegans in Europe (where salt is either not iodized or not iodized at high enough levels) who do not supplement (as well as those who oversupplement) have indications of abnormal thyroid function.1, 2
Iodine is only found inconsistently in plant foods, depending on the iodine content of the soil. Food grown near the ocean tends to be higher in iodine. Iodine is consistently found in only a few foods such as dairy products (iodine solutions are used to clean the cows’ teats and dairy equipment and end up in the milk) and seafood (including seaweed).
Iodine deficiency is not as much of a problem for U.S. vegans as it is for European vegans,1, 2 whose food supply contains less iodine. In the United States, there is now a concern about perchlorate contamination of water and in fresh vegetables. Perchlorate interferes with thyroid function, especially among people with low iodine intakes. You can read more about perchlorate and iodine in the article Perchlorate Controversy Calls for Improving Iodine Nutrition by David M. Crohn, PhD.
Soy and Iodine
There are components in soy, flax seeds, and raw cruciferous vegetables (broccoli, brussels sprouts, cauliflower, and cabbage) that counteract iodine. These components, called goitrogens, cause an enlarged thyroid gland, also called a goiter. Thus, large amounts of soy combined with inadequate iodine intake can exacerbate iodine deficiency.
Recommendations and Sources of Iodine
North American vegans should take a modest iodine supplement; 75-150 mcg every day or every other day should be enough.
Vegan iodine supplements can be found in most grocery or natural food stores. Most vegan multivitamins contain iodine.
You can also get the extra 75 mcg of iodine from 1/4 teaspoon of iodized salt (in the United States; other countries may not iodize their salt at the same levels). If you are already eating 1/4 teaspoon of salt per day on your foods, make sure it is iodized. However, I would not recommend adding salt to your diet just for iodine because it’s generally good to limit salt intake. While studies on sodium intake and overall mortality show mixed results, there is a link between sodium and high blood pressure, and sodium intakes above 2,000 mg a day increase calcium loss in the urine which could increase the risk of osteoporosis. Because of this, people who do not already add salt to their food, should get iodine from an iodine supplement or a multivitamin. Because iodine supplements usually come in amounts of 150 mcg per tablet, taking 1 tablet every other day should suffice. I break up one 150 mcg tablet and take it over the course of a week.
If you regularly eat seaweed (multiple times a week), you will probably get adequate iodine from the seaweed. However, the availability of iodine from seaweed is variable and it can provide too much iodine. Cases of iodine toxicity I’ve seen in scientific journals were mostly from excessive amounts of kelp and kelp tablets. So, like salt, I would not recommend adding seaweed to your diet for iodine.
Avoid intakes in excess of the Upper Limit.
|Dietary Reference Intake (DRI) for Iodine|
|1 – 3||90||200|
|4 – 8||90||300|
|9 – 13||120||600|
|A – Do not exceed the upper limit.
B – mcg = microgram = µg
- For practical purposes, the terms iodide (one molecule) and iodine (two iodide molecules) can be used interchangeably.
- A goiter (enlarged thyroid gland) can be caused by eating both too little or too much iodine. The symptoms of either can also be the same: Hypothyroidism, in which metabolism slows and weight and cholesterol increases. Or hyperthyroidism where metabolism increases resulting in weight loss.
- An iodine deficiency can inhibit brain development in a fetus, so vegan women should ensure a reliable source of iodine.
- Iodized salt has iodine added to it. The package will state that it is iodized. In the U.S., iodine is added to iodized salt at a rate of 76 mcg per 1/4 teaspoon (1 gram) of salt. This amount of salt also provides 500 mg of sodium.
- The salt found in packaged foods is usually not iodized.
- Sea salt, which does not necessarily contain iodine, has the same effects on blood pressure and calcium as table salt.
1.Appleby PN, Thorogood M, Mann JI, Key TJ. The Oxford vegetarian study: an overview. Am J Clin Nutr 1999 Sep;70(3 Suppl):525S-531S.
2. Lightowler HJ, Davies GJ. Iodine intake and iodine deficiency in vegans as assessed by the duplicate-portion technique and urinary iodine excretion. Br J Nutr 1998 Dec;80(6):529-35I.