Roles of Thyroid Hormones:
The thyroid gland makes two hormones: triiodothyronine (T3) and thyroxine (T4).
T4 blood levels are higher than T3 but T3 is four times more potent. When T4 is not converted to T3, low thyroid occurs. An under-active thyroid, typically after age 35, is largely un-diagnosed and untreated.