Iodine is a trace mineral that is critical for the proper function of the thyroid gland. Insufficient levels of iodine may result in goiter, an enlarged thyroid gland. Natural sources of iodine include seaweed, cod, yogurt, and milk. Table salt and bread are often enriched with the mineral, so iodine deficiency is rare in the U.S. Just as low levels of iodine can be harmful to health and to the function of the thyroid gland, high levels of the trace mineral can lead to goiter and hypothyroidism as well. Iodine supplements may interact with certain diuretics, blood pressuremedications, and anti-thyroid medications.