T3-only/ iodine levels

[DippyDame]

Can someone please explain the impact that taking T3-only medication might have on iodine levels given that deiodination is no longer involved in T4 to T3 conversion?

Thank you!

[greygoose]

well, obviously you will have less iodine in the system if you cut out the t4 to t3 conversion, but I think the size of your dose will compensate that. and then you convert t3 to t2, and t2 to t1, and t1 to t0, at a rate of 1 atom iodine for every molecule of thyroid hormone.

and, of course, you need less hormone because your thyroid is not making hormone anymore.

[DippyDame in reply to greygoose]

Excellent greygoose ....that's the answer I was hoping for...I knew you would know!!

I wanted some reassurance that iodine level might be ok

Thank you!

[greygoose in reply to DippyDame]

Pretty sure it will be. It's all recycled again and again and again. Which is why we only need tiny doses.

[helvella Administrator Thyroid UK]

100 micrograms of levothyroxine contain 63.54 micrograms of iodine.

If you converted all that levothyroxine to liothyronine (in a lab or factory!) that would contain 47.66 micrograms of iodine.

That is, it would have 15.88 micrograms less iodine.

100 micrograms of liothyronine contain 56.66 micrograms of iodine.

(This might initially appear odd but it is because a single molecule of liothyronine is lighter than a single molecule of levothyroxine. 671.949 as against 798.853.)

[DippyDame in reply to helvella]

Thank you helvella!

So my intake is 56.55mcg iodine from daily dose of 100mcg lio

NHS quote adult requirement as 140mcg a day

Hopefully my diet and recycled T3 adds sufficient iodine to that....others more

Must do some checking/counting

[helvella Administrator Thyroid UK in reply to DippyDame]

Your logic is fine!

But some of the liothyronine will not be absorbed, some of it - and what it gets converted into - will be excreted as it is.

So 56.55 is significantly above the amount you will actually get and keep.

But by how much is very much a finger in the air job.

[DippyDame in reply to helvella]

Fingers crossed then!!

Thank you for explaining.