Yes, there are T4 receptors!

[HIFL]

Apparently, there are T4 receptors, which means T4 is more than a prohomone!

tiredthyroid.com/blog/2015/...

[faith63]

There may be t4 receptors, but it still needs to be converted to be useful to the body. I don't convert well and for me, t4 just made me feel worse. Many do quite well on t3 alone and was the only way they got their lives back.

[HIFL in reply to faith63]

You misunderstand. T4 has some functions, as T4, WITHOUT conversion to T3. I've read enough posts to know that some people don't do well on T4 at all and prefer T3. BUT, T4 has a role in normal biochemistry. Too much T3 made me ill.

[faith63 in reply to HIFL]

I agree with Dr. Lowe, based on his years of research. Here is what he had to say.

Question: I’m perplexed. You say that T3 can be taken alone without T4, but my endocrinologist insists that our bodies absolutely must have T4 along with T3. He says quite emphatically that without T4 in the mix, I won’t get the full benefits of my thyroid hormone therapy.

Dr. Lowe: I respectfully disagree with your endocrinologist. Studies indicate that T4 is of no use to anyone except, figuratively, as a storage unit for the metabolically-active thyroid hormones T3, T2, and possibly T1. When T4 ends its long ride through the circulating blood, it enters cells. There, enzymes convert it to T3, and, after a while, other enzymes convert T3 to T2. The T2 becomes T1, and eventually T1 becomes T0 (T-zero). T0 is just the amino acid back bone(called "tyrosine") with no iodine atoms attached. Because it has no attached iodine atoms, T0 is no more a hormone than is T4.

Rather than being a hormone, T4 is a “prohormone.” That means that enzymes have to convert T4 to T3 before T4 benefits us. T4 is no more a hormone than beans in an unopened can are a food. For all practical purposes, canned beans become food only when a can opener frees them so you can eat them. Hence, T4, like canned beans, only potentially benefits us, but actually does so only after being freed from its metabolically unusable form.

Your endocrinologist may say that T4 is a gentler way to get T3 into your body. This to me, however, is a specious argument. When taken

properly, T3 can effect one as gently as T3 derived from T4.

[faith63 in reply to HIFL]

I didn't misunderstand..i don't believe t4 has any unique functions of it's own.

[Glynisrose]

Do you really believe in the research? Levo is T4 alone and synthetic, so does the body recognise it as a pituitary hormone? There may well be T4 receptors but there is also the question of whether levo works long term!!

[Treepie in reply to Glynisrose]

As they always say " More research needed".

[HIFL in reply to Glynisrose]

Yes, the references are pretty convincing. Levo is bioidentical to what's produced in the body, IF you have enough stomach acid to break it down. Levo is a thyroid, not pituitary hormone. TSH is the pituitary hormone. And no, I don't believe levo alone long-term is a good idea. I think everyone should take T4+T3, with some needing more T3 than others.

[PR4NOW]

Actually HIFL is correct. The science is pretty good that T4 has some other uses in the body besides being a prohormone in the thyroid cycle. It appears to be involved in the regulation of the FAD cycle along with some non-genomic reactions as described in Barbara's article. It also may bind to some receptors for genomic action but this is still largely theory and not fully understood or proven. The human body is extremely complex and there is a lot of redundancy or multiple pathways to accomplish a task. The fact that some people can survive quite nicely on T3 only and we don't really understand why they need T3 only or how the body compensates for the lack of T4s other actions just illustrates the deficit of our knowledge. In reality we have barely scratched the surface, we are still on bended knees peeking through the keyhole trying to figure out what is on the other side of the door. I would be wary of making dogmatic proclamations, that is the mistake endocrinology has made for years which is responsible for our needless suffering. Science is woefully ignorant when it comes to a thorough understanding of the various parts of the endocrine system and how they all interact. All we know are little bits and pieces and even those are subject to further refinement. None of us have all the answers, we are all explorers in uncharted waters. PR

[Hypomom]

tiredthyroid.com/rt3-7.html