Iodine

What is iodine?

Iodine is a trace mineral that the body cannot make. According to the NIH Office of Dietary Supplements, it is an essential component of the thyroid hormones thyroxine (T4) and triiodothyronine (T3), which regulate metabolism, protein synthesis and enzyme activity. When iodine intake is too low, the thyroid enlarges (goiter) as it tries to trap more iodine from the blood.

Iodine is found in seafood, seaweed, dairy products and eggs, and it is added to iodized salt. In the United States, iodized salt provides about 45 mcg of iodine per gram, but most salt in processed foods is not iodized, and specialty salts such as sea salt and Himalayan salt usually are not either. The Daily Value for adults is 150 mcg.

What the research says

Iodine’s role in thyroid function and early brain development is firmly established, which is why we rate the general evidence for iodine as strong. Adequate intake is especially important during pregnancy and breastfeeding, when needs rise. Iodine deficiency in pregnancy can affect a baby’s development, which is why some prenatal vitamins include it.

The evidence does not extend to oral health. We found no clinical trials showing that taking iodine by mouth improves gum health, tooth strength or breath. In dentistry, iodine is used topically, as povidone-iodine antiseptic solutions, which is a completely different use from swallowing a small amount in a tablet.

More iodine is not always better. Both too little and too much can disturb thyroid function. The ODS sets the tolerable upper intake level for adults at 1,100 mcg per day, and people with existing thyroid disease can be sensitive to amounts below that. Iodine supplements can also interact with certain medicines, including antithyroid drugs such as methimazole, and potassium iodide adds potassium that may matter for people on some blood pressure drugs.

How it’s used in supplements

Iodine usually appears as potassium iodide or sodium iodide, which the body absorbs almost completely; the ODS cites a small study showing about 96% absorption of potassium iodide. Many multivitamins contain 150 mcg. Kelp and seaweed supplements can contain highly variable and sometimes excessive amounts.

A dental supplement adding 50 mcg of iodine is unlikely to cause harm in a healthy adult who otherwise eats a typical diet, but it also does not address the product’s stated goal. If you already take a multivitamin or prenatal vitamin, check your total iodine intake. People with thyroid disease, those taking thyroid medication and anyone who is pregnant or breastfeeding should talk to a doctor before taking additional iodine.

The best way to cover iodine needs for most people is through food: use iodized salt at home in moderate amounts and include dairy, eggs or seafood in the diet.