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Iodine and the Thyroid

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Updated June 02, 2014

Man preparing food in the kitchen
Eric Audras/ONOKY/Getty Images
by Mary Shomon

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% of US citizens had iodine deficiency. The followup NHANES III survey, conducted between 1988 - 1994, found that 11.7% 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% in 1974 to 7% 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.

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