Clarification about T4 to T3

I have been reading alot about thyroid problems. I come across an article which says that the reason we still suffer with symptoms ie, brain fog, tiredness, hairloss, coldness, tingling in hands etc is that the body has trouble converting T4 into T3 even though the blood tests come back normal TSH and T4.

I explained this to my doctor and he just thinks im depressed. I kept on asking for him to check my T3 levels but he said they do not test for this as its to expensive. However he has now refered me on to the Endo specialist who he said will do these tests im asking for.

Can you clarify if the statement about T4 conversion to T3 is correct. I need to be armed with the facts before I see the Endo in January. (Suzy Cohen on you tube explains this)

12 Replies

  • Diva, yes if T3 is low it's often the cause of those symptoms. That's why it is so infuriating that only TSH or TSH & FT4 are tested because without a FT3 measurement it is simply not possible to say whether T4 is converting to T3 well, or at all.

    I can't believe frequent GP appointments for ongoing symptoms are less expensive than FT3 testing which may identify a problem.

  • Plus the various other conditions we are treated for because 'they are nothing to do with the thyroid'.

  • When I went for my blood test I asked for certain ones to be checked and when I went back for my results and realised that they only test T4 and TSH. I told the doctor this is a complete waste of time and money. Gps need to have further training on Thyroid conditions this may help to cut down how much they are spending on needless tests and medication. My tingling of my hands he sent me to have a carpel tunnel test. Results not carpel tunnel.

  • Tingling in your hands could be caused by B12 deficiency. Since this can cause permanent neurological damage if it is not treated quickly it is important to find out if your B12 is low and repair the deficiency as soon as possible. Make sure you get a copy of the result and the reference ranges and then post the results in a new question.

  • I have heard that T4 is converted to T3 in the gut. And if you have leaky gut this cannot occur. You might try healing your gut by "rejuvenating your Microbiome".

  • How do you know if you have a leaky gut. Thanks for your reply

  • Hi there

    I'm certainly no expert myself, just figuring it all out as I go along after being diagnosed in June 2014 with Hashimoto's, which is auto-immune, but am noticing big improvements to the way I feel, following healing the gut principles. (regenerating your Microbiome ) From all my readings it seems that auto-immune diseases probably start in the gut. I'm focusing on gut health, lowering inflammation, stabilizing blood sugar, reducing stress and having more pleasure in my life.

    This is quite a long Google Hangout called Gut Thrive which I found very inspirational.

    Most of my gut health reading has been through Chris Kresser (Paleo), Dr. Izabella Wentz

    Christa Orecchio and Dr. Jack Tips.

    Best wishes to you on your journey of reclaiming your health,


  • Suzrou, a leaky gut may hinder absorption of thyroxine but T4 to T3 conversion takes place in the thyroid gland, brain, liver, kidneys and heart.

  • I had all the symptoms that you described and felt like I was going mad as my blood results were classed as being "normal" or slightly over. Having been advised on here, I begged my Endo (and I mean begged) to trial T3 meds alongside a lowered dose of thyroxine and feel so much better! No brain fog or feeling low but it's early days for me (only started meds this week) but feel like I can function in daily life! Insist on a trial when you see your Endo in January, they might be reluctant but it's worth trying if you feel low!

    Good luck and hope it helps

  • I have read that (forgive that I can't remember which doc said it- but a wise and helpful analogy) t4 is like a can of beans. It is a storage hormone likened to being stored in the tin. It is only when the can is opened and an iodine (I think) atom (or possibly ion) drops of that the can is open and the beans t3 is released to the cells all over the body including the brain that need it for energy. There are a number of things that can stop this from happening. Some people have a gene or 2 copies of a gene that inhibit conversion, low iron and some other things can get in the way of the process as can high cortisol from stress and inflation in the body causing high Crp. (Inflammation markers) there is a paper that someone put on here that is technical, but explains it all. I am away from my laptop at the moment - this is from memory - I hope it helps. I will dig out the paper later unless someone else has it to hand. Sandra

  • And if hands tingling can b a sign of hypothyroid, but also low B12.


  • Thank you Sandra. I will take all this info when I see the specialist in January.

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