Iodine is the largest atom in the human body. It has unique features that power multiple functions, not just thyroid.  While the thyroid system utilizes a large proportion of the body’s total iodine, the following tissues require iodine and cannot function properly without it: salivary glands, breast and prostate, stomach (secreted into the stomach during digestion), other locations in the gut, choroid plexus in the brain (which lines the mysterious fluid-filled ventricles), and other places. Every cell of the body is supplied with iodine when levothyronine (T4) is converted to liothyronine (T3), T2, and probably T1, releasing Iodide ions. 

The World Health Organization’s position is that “iodine is the leading cause of reversible brain dysfunction in children”. Pre-natal or post-natal iodine or thyroid deficiency can cause problems with brain development, some of which is irreversible. Adult brain and optimal health require proper amounts of iodine while reducing the toxic effects of halide competitors bromine, chlorine (perchlorates) and fluorine.