Thyroid UK

Vitamin B12 - Conversion of T4 to T3?

My special needs son had an appointment with a new Endo this morning and hopefully this could be a good relationship. We were talking about my son's level of B12 and I mentioned that someone on this forum had said that there was evidence that T4 was not converted to T3 unless your B12 was over 500. He said he would be interested to see this information as he had not been informed of this, and would I please send him this with a quote as to where it came from. I have been looking for the past couple of hours and cannot find who sent in this information. Can anyone help me and possibly give me a website for this. Also, if anyone has any other information that I could slip in, that would be good as I think he is fairly amenable to new information. He did concede that B12 was very important to conversion. We also talked about prescription drug depletion and I will also enclose the list posted by hamster yesterday - thank you hamster. Janet.

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I don't know if this link will be helpful although it doesn't state a number for B12. I think the usual range is up to about 900 but I know we should aim towards the upper level.

This is another link


Hi Janet, I have never seen a link claiming what you have said. In fact, I try not to put too much emphasis on the serum B12 test at all, as it is so unreliable (other than for identifying very deficient states). What you might want to focus on for your son is 1) the unreliability of the serum B12 test, and 2) the usefulness of other more sensitive tests.

Some links for 1)

More sensitive tests 2) - Active B12, MMA, homocysteine

Also, I have been interested in the case studies on the Axis-Shield website, they are the makers of the Active B12 test:

If you scroll down to the hypothyroidism case study, you will see they make an interesting claim about hypothyroid patients having a much lower than normal amount of active B12 versus inactive B12 in their blood. This could explain the reason why so many hypo patients test normal for total serum B12, when in actual fact they might have next to none active B12. Obviously these people are trying to sell their test, and I have been scouring the internet trying to find a study that backs up this claim. Maybe you could contact Axis Shield and ask them if such a study exists? It's certainly a talking point with your doctor, at any rate. Might be worth getting referred for the Active B12 test.



Hi Shaws and Hamster,

Thank you both very much for the links you have given me. They will be very useful to my cause, which is to get my son's T3 a little higher than 3.5. This may not be possible as he has pituitary problems , but if I can get his vitamin levels at optimum, then this would be a help. The person who stated that Vit B12 should be 500 before T4 could convert to T3 did not give a link and I had hoped that they would get back to me with one. They also stated that in Japan the lowest level was 405, but of course their measurements are different to ours. Janet.


A study for you that references the normal level in Japan as being 500 - 1300 pg/ml

Give him that to chew on.

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