#1 Question ?
What is the structural difference between T4 and T3 ?
One iodine molecule ( T4 has 4 iodine molecules and T3 has 3 )
#2 Question True/ false
T3 is the active metabolic form of thyroid hormone.
Answer - True,
T4 is the inactive primary form of thyroid hormone produced in the thyroid gland. The
T4 is then slowly converted to T3 by enzymes in our tissues by removing 1 iodine
#3 Question ?
Why not cut out the "middle man , T4 " and just take the active form of the hormone T3 ?
Answer ? The short answer is that it is just not safe for every one. T3 is almost 100% absorbed
and produces an elevated T3 level with every dose. This can produce extra demands on
a persons heart.
T4 is a longer lasting hormone that slowly converts to the metabolically active , T3 ,
delivering a steady stable supply of T3 to our tissues. There is a small percent of
people who genetically are unable to convert T4 to T3 , and will benefit from taking a
medication containing T4 and T3 such as Thyrolar .
Is there any reason for ever using pure T3 ?
Yes. I used Cytomel ( T3 ) , because of its short half life , as part of the process in
evaluation of patients with thyroid cancer.
There is some evidence that some people may need to take a little bit of T3 to get the full benefit from thyroid replacement. I have attached an abstract of an article supporting the idea below.