Iodine

Iodine is an essential micronutrient required for the biosynthesis of thyroid hormones (triiodothyronine/T3 and thyroxine/T4)[3][5][7]. Iodine is transported into thyroid follicular cells as iodide, concentrated via the sodium-iodide symporter (NIS), then oxidized by thyroid peroxidase (TPO) and incorporated into tyrosine residues on thyroglobulin in the thyroid follicular lumen[1][3][5][7]. Coupling of iodinated tyrosines forms the thyroid hormones, which are released into the circulation and regulate metabolism, growth, and development[1][3][4][5][7]. Insufficient iodine leads to decreased hormone production, goiter, and developmental disorders, particularly in pregnancy and early childhood[3][5]. While crucial for health, neither iodine in its elemental nor ionic form is a receptor, enzyme, transporter, or comparable molecular target; it is a cofactor/substrate in hormone biosynthesis. Key note: Iodine, as described above, is not itself a *therapeutic target* but is indispensable as a substrate in a multistep enzymatic pathway—with proteins such as the sodium-iodide symporter (NIS), thyroperoxidase (TPO), and thyroglobulin serving as true molecular targets within this pathway[3][5][7].

Other names

Elemental iodineI^−^ (iodide, biologically relevant form)I_2_

Supplementation: provides bioavailable iodine to enable thyroid hormone synthesis Large doses: acutely inhibit thyroid hormone release (Wolff–Chaikoff effect) Radioactive iodine: destroys thyroid tissue by beta emission