Thyroid~ a very important gland responsible for many body functions!
The thyroid produces both T4 and T3 but T3 is approximately three times more potent that T4 and is the active form of the hormone.
In order to get more T3, a healthy body will convert roughly 60% of the circulating T4 into T3. This process occurs most in the liver by an enzyme called iodothyronine 5' deiodinase. The remaining T4 is converted to T3 in a healthy GI tract. If you have a healthy liver and GI tract, you'll be optimally converting T4 into T3.
Common reason the liver may not be converting T4-T3
Advanced glycation end products (AGES)
High carbohydrate diet
Leaky gut syndrome
Mineral and vitamin deficiencies (selenium, zinc, iron, vitamin A, B-6, B12
Heavy metals (mercury, lead, etc..)
Petrochemicals and other toxins
Growth hormone deficiency
Drugs (propylthiouracil, methimazole, dexamethasone, propranolol, amiodarone, birth control medication, estrogen, lithium