How is thyroid hormone made?
Thyroid hormone is produced by the thyroid with the use of iodine ingested in food. Because iodine is generally found in low levels in the American diet, iodine is now added to salt (iodized salt) to prevent iodine deficiency. Thyroid hormone is produced by the thyroid in two forms, thyroxine (T4) and triiodothyronine (T3). T4 has very little hormone activity in the body until it is converted to T3 in the liver and body tissues. Much of the T4 and T3 is bound to protein in the blood and this is released when it is needed.
