Your thyroid gland, located just above the middle of your collarbone, needs iodine to make thyroid hormone, which maintains normal metabolism in all cells of the body. Principally found in sea water, dietary iodine can be scarce in many inland areas, and deficiencies were common before iodine was added to table salt.
Iodine deficiency causes enlargement of the thyroid, a condition known as goiter.
However, if you are not deficient in iodine, taking extra iodine will not help your thyroid work better, and it might even cause problems. For reasons that are not clear, supplementary iodine might also be helpful for cyclic mastalgia. Seafood and kelp contain very high levels of iodine, as do salty processed foods that use iodized salt. A typical therapeutic dosage of iodide or iodine is 200 mcg daily. Three clinical studies indicate that supplements providing iodine may be helpful in treating cyclic mastalgia.