Iodine deficiency in the characteristic swelling or hyperplasia of the thyroid gland, or goiter. In mild iodine deficiency, levels of triiodiothyronine (T) may be elevated in the presence of low levels of levothyroxine, as the body converts more of the levothyroxine to triiodothyronine as a compensation. Some such patients may have a goiter, without an elevated TSH. The introduction of iodized salt since the early 1900s has eliminated this condition in many affluent countries; however, in Australia, New Zealand, and several European countries, iodine deficiency is a significant public health problem. It is more common in developing countries. Public health initiatives to
Isotopes of iodine Isotopes of iodine There are 37 known isotopes of iodine (I) from I to I; all undergo radioactive decay except I, which is stable. Iodine is thus a monoisotopic element. Its longest-lived radioactive isotope, I, has a half-life of 15.7 million years, which is far too short for it to exist as a primordial nuclide. Cosmogenic sources of I produce very tiny quantities of it that are too small to affect atomic weight measurements; iodine is thus also a mononuclidic element—one that is found in nature only as a single nuclide. Most I derived radioactivity on Earth is man-made, an