Natural T4 vs synthetic T4

[tcpace]

All the experts say there two are essentially the same. But is that definitely the case? Some people (my wife for one) can't tolerate synthetic T4. At present she's T3 only. Just wondering if she might be able to tolerate Armour or other NDT, eg. because the natural thyroxine is bound to a transport protein whereas the synthetic form is a sodium salt? Or maybe it's just that she's not a very good converter of T4 (whether natural or synthetic) to T3. Thoughts anyone.

[greygoose]

That's something she'll only know if she tries. No-one can predict in advance how any of us are going to react to any form of thyroid hormone replacement.

Myself, I cannot tolerate T4 whether natural or synthetic. And, it wasn't a conversion problem, either. Even on a high dose of T3 I have never been able to successfully reintroduce levo with it.

I'm afraid she's just going to have to do her own experimenting, and try it to see.

[radd]

tcspace,

It isn't really a fair comparison because natural T4 is only available within NDT that also contains T3 and other hormones. Even tiny amount of T3 is known to change the deoidinase behaviours positively that results in more T4 - T3 conversion.

They are biologically similar but most T4 from a healthy thyroid gland is bound to TBG. A tiny amount of T3 is made by the thyroid gland and the rest comes from conversion of T4 after it is freed. This system allows a drip feed of active thyroid hormone when we need it.

There is also thought that synthetic T4 can be taken as a whole daily dose dumped into the blood stream at once, as is only the storage hormone and old research says even a whole weeks worth can be medicated in one day a week with zero ill effects! Except we have members who have turned unsuccessful medicating of Levothyroxine into successful, alleviating symptoms after split dosing their daily Levothyroxine. 

Many feel better for split dosing their T3 meds (I certainly did as couldn’t tolerate that T3 hit) and now medicating NDT I can take one daily dose that works well. This I put down to the delay in hormone release form thyroglobulin. NDT is also said to contain other thyroid hormones and metabolites that contribute towards good wellbeing.  

Good utilisation of thyroid hormones is also down to the ratio of T4:T3, that like the dose is individual to us all. In T4 mono-therapy, people often need higher doses to chase enough FT3, but as FT4 levels rise over that 'correct' ratio, the T4 - T3 conversion enzyme gets progressively less efficient, eg the more T4 you medicate over your 'right' amount, the less conversion overall. These are the people who need a little T3 added to their Levo.