Iodine

What Is Iodine?

Iodine has one well-established job in the body, and it is a large one. The thyroid gland traps iodine from the blood and attaches it to the amino acid tyrosine to build two hormones: thyroxine (T4), with four iodine atoms, and triiodothyronine (T3), with three. An adult body holds about 15 to 20 mg of iodine, most of it in the thyroid.

What Thyroid Hormone Does

Thyroid hormones set how fast cells use energy and make protein, and they control many enzymes. Before birth and in the first years of life they also steer the growth of the brain and the skeleton. That is why a shortage in pregnancy does damage that a shortage in adulthood does not.

The thyroid needs a second mineral to finish the job. Most of the hormone it releases is T4, and selenium-containing enzymes remove one iodine atom to turn it into the active T3, so selenium and iodine work as a pair.

What Happens When Iodine Is Low

When iodine is low, the pituitary gland keeps signaling the thyroid to work harder, and the gland grows. That swelling in the neck is a goiter, often the first visible sign. If the shortage goes on, hormone levels fall and hypothyroidism follows: tiredness, weight gain, feeling cold. In pregnancy, severe deficiency can cause lasting intellectual disability and stunted growth in the child.

The WHO calls iodine deficiency the most common preventable cause of brain damage in the world. Its answer since the 1990s has been to add iodine to salt, and most countries now do. Mild deficiency is still common in parts of Europe, where iodized salt is less widely used.

Cutting Salt Without Losing Iodine

Eating less salt does not have to mean less iodine. The WHO advises both: cut total sodium, and make the salt you do use iodized. Most of the salt people eat comes from processed food, which in the US is rarely made with iodized salt, so the salt shaker at home matters more for iodine than the sodium total suggests.

Who Is Most Likely to Be Low in Iodine

Pregnant and breastfeeding women need half again to nearly twice as much as other adults, and the American Thyroid Association advises a daily 150 µg supplement in the US. People who eat no dairy, eggs or seafood, such as vegans, and people who use only non-iodized salt are the other main groups. Dairy such as milk and white fish such as cod are the simplest food sources to add.

Common Iodine Mistakes

More is safer. Too much iodine can also cause goiter, an underactive or overactive thyroid, and thyroid inflammation. Kelp supplements and seaweed snacks eaten daily are the usual way people overshoot.

Gourmet salt counts. Sea salt, pink salt and flaky salts are rarely iodized. Switching to them from iodized table salt quietly removes a source.

Potassium iodide pills for radiation are a daily supplement. They protect the thyroid from radioactive iodine after a nuclear accident, at high doses, and should be taken only when public health officials say so.