Iodine and Your Thyroid: What You Need to Know

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Iodine is an essential element that enables the thyroid gland to produce thyroid hormones.

Three iodine molecules are added to make T3 (triiodothyronine), and four for T4 (thyroxine)—the two key hormones produced by the thyroid gland—so iodine is essential to the production of these two hormones of the master gland of metabolism.

One needs the proper amount of iodine for optimal thyroid function.

A severe iodine deficiency can cause hypothyroidism, and even developmental brain disorders and severe goiter.

Less severe iodine deficiency is linked to hypothyroidism, thyroid enlargement (goiter) and hyperthyroidism. At the other end of the spectrum, excessive iodine intake—both severe and moderate—is also associated with hypothyroidism and goiter.

Iodine Deficiency

There are many areas around the world where soils are deficient in iodine, and iodine must be added to the diet—usually through iodized salt. In the U.S., for example, the area around the Great Lakes used to be known as the goiter belt because the soil is particular iodine-deficient, and this resulted in higher incidence of goiter among residents of the area. Earlier in the 20th century, however, iodized salt almost wiped out iodine deficiency in the U.S. entirely.

Other countries have not had such concerted iodization programs. In 1999, global health experts announced that iodine deficiency continues to be a serious threat to global health.

Insufficient iodine is, in fact, considered is the most common—yet also most preventable—cause of brain damage throughout the world, with 1.6 billion people at risk.

Children with iodine deficiency and its resulting hypothyroidism can suffer from stunted growth, with mental retardation and problems in movement, speech or hearing.

Worldwide, iodine deficiency actually affects some 50 million children. When a woman with iodine deficiency becomes pregnant, she risks miscarriage, stillbirth and mental retardation in her baby. Even what's considered a mild iodine deficiency can hamper the growth of children's brains, reduce their IQ, and cause learning disabilities. The World Health Organization estimates that some 1 billion people around the world are at risk of health problems due to iodine deficiency. In Latin America and the Caribbean, for example, as many as 25 percent of the population -- a total of almost 200 million people—are at greater risk of goiter, at minimum.

While iodine deficiency was not common in the U.S., it is again on the rise here as well. The first National Health and Nutrition Examination Survey (NHANES I), which took place between 1971-1974, found that just 2.6 percent of US citizens had iodine deficiency. The followup NHANES III survey, conducted between 1988-1994, found that 11.7 percent are iodine deficient. The October, 1998 issue of the Journal of Clinical Endocrinology and Metabolism reported that over the previous 20 years, the percentage of Americans with low intake of iodine has more than quadrupled.

Of particular concern is the fact that the percentage of iodine-deficient pregnant women has increased from 1 percent in 1974 to 7 percent in 1994. Maternal iodine deficiency is particularly dangerous to a developing fetus. The researchers do not have a cause for the drop in levels, though it is suspected that reduced salt in the diet, plus a reduction in the use of iodine as a food ingredient, may be responsible. This trend, however, may necessitate concerted efforts to increase iodine levels in people at risk of deficiency even in the U.S.

What About Iodine Supplementation?

The relationship between iodine and the thyroid is complicated.

Some alternative practitioners simplistically declare that all thyroid patients should take iodine -- or an iodine-containing herb like kelp.

That practice can be problematic for many people, because many cases of autoimmune thyroid disease—which is by far the most common cause of thyroid conditions in the United States—are not due to iodine deficiency. The likelihood that your thyroid problem is caused by iodine deficiency is a factor of your geographic location, diet, and use of salt and iodized products, but the odds are, you are not iodine deficient.

Your physician or nutritionist can test your iodine levels via a urinalysis test, if you wish to be evaluated. If, like many patients, you decide on your own to try kelp, iodine, or one of the many thyroid-supporting supplements (almost all of them contain high amounts of iodine or kelp), to see if they can help you, be aware of the risks. A percentage of patients are very sensitive to iodine/kelp supplementation, and find that it aggravates their thyroid problem.

Personally, I'm one of those people who simply does not do well with much in the way of supplemental iodine. I do fine with food that contain iodine—such as seaweed or seafood. In fact, I periodically find myself craving sushi and a good seaweed salad, and can eat it with no after-effects whatsoever. But the several times I have tried iodine or kelp supplementation in any form—beyond the very small amounts of iodine contained in some supplements—I have had what I call an "iodine crash."

Within a day, I noticed my thyroid enlarging slightly (goiter), and feeling tender. Within three days, I became exhausted and achy all over my body. Most of the thyroid support supplements have high amounts of iodine, or kelp, claiming that these are essential nutrients for the thyroid. Be careful—they may be a help to you, but like me, you may also be sensitive to supplemental iodine in pill form, and find yourself having an iodine crash.

A Word From Verywell

Some people are so sensitive to iodine that they really shouldn't even take the small amount of iodine you would find in most multivitamins. For that group, there are several supplements that contain no iodine (they also happen to contain no iron as well, which means they can safely be taken at the same time as your thyroid medications). (Note: if you are taking iron supplements, you need to take them at least 3 to 4 hours apart from your thyroid medication.)


Laurberg P, et. al. "Environmental iodine intake affects the type of nonmalignant thyroid disease," Thyroid. 2001 May;11(5):457-69