Does t4 have a special use in the body or is it just the inactive form of t3?

[lisan1]

Does t4 have a special use in the body or is it just the inactive form of t3? Like do you need a good t4 level for hair and skin for example?

[diogenes Remembering]

The main reason that the thyroid secretes mainly T4, and the T4 resource in blood is so much higher than T3, is that if humans lived a T3-only life in health, there would be a much poorer and less stable situation. T4 acts as a stabiliser/smoother so that the right amount of FT3 for the conditions is always present through conversion to T3 wherever required.

[lisan1 in reply to diogenes]

So if you're taking both levo and lio for hypothyroidism does it matter if ft4 is at lowest or even under reference range as long as Ft3 is well within?

[diogenes Remembering in reply to lisan1]

I don't think it matters too much, so long as there is some T4 there. T4 may have other non-classical - ie not directly thyroidal roles to play. These are poorly understood.

[DippyDame in reply to diogenes]

Thank you diogenes , just a thought. A number of us are T3-only ( not in health I guess, I have a form of RTH so currently on 100mcg) are we to expect much poorer and less stable health without the presence of T4. Labs return FT4 as suppressed.

Might that explain difficulty in achieving a therapeutic dose?

[diogenes Remembering in reply to DippyDame]

There is a danger of instability, because the T3-only dose might need altering when the patient encounters a nonthyroidal disease (Covid?). With combination, there is wriggle room for T4 conversion to be reduced, thus responding within the body, rather than having to adjust outside-the-body dosing with T3 only.

[DippyDame in reply to diogenes]

Thank you diogenes that is hugely helpful. Much appreciated.

I think at age 76, and after possibly a lifetime of increasingly low cellular T3, my body has rebelled and given up trying to respond to anything thyroid related...it depends on outside-the- body help!!

I will feel more comfortable occasionally tweaking my dose if the need arises.

I ended up in A&E a few weeks ago, pain, exhaustion etc , but tests and scans all proved negative and I was sent home with a bag of analgesics! My GP said, "I've no idea what is wrong with you"!

A few days later it dawned on me that my T3 cellular level had probably hit the floor. For months, during covid restrictions, I had been dealing with (at 200 miles + distance,) my 89 year old brother's brain cancer diagnosis, his eventual death and subsequent funeral and estate affairs. He lived alone.

After increasing my T3 dose I very slowly improved again.

Without this amazing forum I would have known neither what my problem is nor how to deal with it.

Best...

DD

[SlowDragon Administrator]

Many members on levothyroxine plus T3 find it’s important to have good Ft4 and Ft3 levels, especially with suppressed TSH

A few people seem ok with lower Ft4, nearer bottom of range

A small number of memories prefer just taking T3, then Ft4 can be extremely low

[jimh111]

I've been on L-T3 only and noticed little difference from combined L-T3 / L-T4, perhaps the gut responds a little more to T4. However, whilst T3 binds to thyroid hormone receptors in the nucleus T4 rather than T3 binds to the αVβ3 integrin receptors on the cell membrane. Little is known about what these do BUT recent research has shown these receptors have a role in promoting cancer and T4 is carcinogenic in a linear fashion. Of course it is perfectly natural to have T4 but it appears higher levels (as opposed to T3) promote cancer. I will be writing this up in the next few months.

I've always thought the standard therapy for primary hypothyroidism of high normal fT4 giving average fT3 was a good solution, not perfect but works fine for most patients. In light of more recent research I'm now of the opinion that we should avoid our fT4 going into the upper quartile of its reference interval. This is a complex subject so I will take my time writing it up. It shouldn't cause panic but neither should it be ignored. The bottom line is that levothyroxine monotherapy should be abandoned for most patients.

[wellness1 in reply to jimh111]

I look forward to seeing this information when you have a chance to post it.

[Mamapea1 in reply to jimh111]

Very interesting information...I very much look forward to reading your finished article. I think many on here would already agree with your bottom line, just through their own experiences (!) You live, you learn, but it's always good to hear of new scientific research...we need all the help and knowledge we can get. Thank you.

[Wired123 in reply to jimh111]

This is interesting and worrying at the same time. Is this strictly related to Levothyroxine FT4 elevation or could someone who naturally produces more FT4 (I’m sure there are some who are naturally at the top of the reference range)?

The reference range is made up of the healthy population after all so some will be quite high in FT4 naturally.

[jimh111 in reply to Wired123]

It's T4 whether it comes from the thyroid or tablets.

[DippyDame in reply to jimh111]

Interesting Jim!

[jgelliss]

Great question. Personally for me from my experiences after my TT I tried both T4 with T3 combo . And T4 suited me the best. I felt that my brain worked much better with T4 and with T3 I felt lethargic brain fog. With T3 I was hungry all the time excitable muscle /joint pain ,fatigue.

With T4 sole I have more energy. I'm more interested to do things and take interest in things I didn't when Even a tiny dose of T3 was added. Muscle/joint pains subsided.

I was explained by a very knowledgeable member of our forum. That when my healthy thyroids worked well it made more T4 and whatever amount of T4 converted to T3 was enough for my body. Which made alot of clarity for me.

I'm glad I tried it. Essentially I was my own rat lab. And learned what works best for me. I must add that the right nutrients in the right amount makes a huge difference too.

Best Wishes.