Iodine

Iodine is a chemical element and an essential trace nutrient required for the production of thyroid hormones. In the body and in many foods, iodine is commonly present as iodide, the negatively charged ion I⁻, rather than as elemental iodine, I₂. After ingestion, iodine compounds are largely converted to iodide, which is readily absorbed and enters the circulation .^1,2

The thyroid gland actively concentrates iodide from the blood using the sodium-iodide symporter. Within thyroid follicles, iodide is transported toward the follicular lumen, where thyroid peroxidase catalyzes its oxidation and incorporation into tyrosine residues within the protein thyroglobulin. The resulting iodinated residues are subsequently coupled to form the thyroid hormones thyroxine (T4) and triiodothyronine (T3) .^1,2

Iodine's established physiological importance arises primarily from its role as an essential structural component of thyroid hormones. These hormones regulate metabolic processes throughout the body and are particularly important for normal growth and nervous-system development. Most of the body's iodine stores in an iodine-sufficient adult are located in the thyroid gland .¹

Iodine and iodide are related but not identical terms. Iodine refers to the chemical element in general, whereas iodide specifically refers to iodine in the I⁻ ionic form. In nutrition, however, “iodine” is commonly used as the general name for the nutrient regardless of the particular iodine-containing compound in which it is consumed .^1,2