Iodine Nutrition — More Is Better

In normal adults, the daily production rate of the two biologically active thyroid hormones, tetraiodothyronine (which is better known as thyroxine and has four iodine atoms) and triiodothyronine (which has three), is approximately 100 μg and 30 μg, respectively. All of the thyroxine, but only about 20 percent of the triiodothyronine, is produced by the thyroid gland; the remainder of the triiodothyronine is produced through the extrathyroidal deiodination of thyroxine. A minimum of approximately 70 μg of iodine is therefore needed to produce these two hormones in the thyroid gland each day. But more than that is required, because iodine . . .