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.
The official US recommendations for daily intake of iodine are as follows:
Iodine deficiency is rare in developed countries today because of the use of iodized salt.
Seafood and kelp contain very high levels of iodine, as do salty processed foods that use iodized salt.
Most iodine is in the form of iodide, but a few studies suggest that a special form of iodine called molecular iodine may be better than iodide.
A typical therapeutic dosage of iodide or iodine is 200 mcg daily.
Three clinical studies provide weak evidence that supplements providing iodine may be helpful in treating cyclic mastalgia.1 These studies suggest that either iodide or iodine (the pure molecular form) might be useful. In the one double-blind, placebo-controlled trial among this group, a study that enrolled 56 individuals, molecular iodine was found superior to placebo in relieving pain and reducing the number of cysts.
Another of these studies compared molecular iodine to iodide. Molecular iodine was no more effective than iodide, but was deemed superior because it induced fewer side effects and did not affect the thyroid.
When taken at the recommended dosage, iodine and iodide are safe nutritional supplements. However, excessive doses of iodide can actually cause thyroid problems, including both hypothyroidism and hyperthyroidism. There is also a speculative link between excessive iodide intake and thyroid cancer. For these reasons, iodide intake above nutritional recommendations is not advised except under physician supervision.