IODINE
Iodine is absolutely vital for proper thyroid function, and its deficiency is probably the most dramatically visible of all, as it produces goiter, a pronounced swelling of the thyroid gland, which is located in the front of the neck. Severe cases cause mental retardation, even cretinism, and are thus among the most devastating of all trace-element deficiencies. Although iodine deficiency was virtually eliminated in the developed world in the 1920s through the brilliantly simple expedient of adding a pinch of iodine to our commercial table salt, it has been making a "comeback" in recent years and thus represents a growing threat to good health even in some Western countries.^10,11 It has always been a major health problem in most underdeveloped countries. (By the way, it's pronounced "eye-oh-deen," not "eye-oh-dine." The latter pronunciation applies only to the antiseptic tincture you buy at the drugstore.) A reasonable amount of supplemental iodine is 100 mcg/day.