Thyroid UK
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Vitamin B12

Hello, I have been taking Vitamin B12 in the form of methylcobalamin, 1000mcg per day, and my recent blood test results show a value of 967 pg/mL of serum B12 (reference range 191-663 pg/mL). My doctor's advice is to discontinue taking this supplement as even though there are no studies showing a high level of B12 is toxic, we still don't know the precise effects on the body.

Since I'm vegan and I have a tendency to a high homocysteine level, I don't really know what to do.

I've also read that B12 in the form of methylcobalamin is good for lowering high homocysteine levels, in the form of adenosylcobalamin it is good for mitochondria (energy) support, and I haven't yet really understood what hydroxycobalamin is good for....and if it's at all helpful

Thanks for your advice!

2 Replies

Martina, PA Society recommend B12 1,000 is optimal. There is no evidence that one can overdose on B12.


Once you are supplementing the serum tests are of little or no value. The results are skewed. What is getting into the cells is important - and only 20% of that result will be available at a cellular level. Docs have yet to grasp this important fact. You need to be taking a GOOD B Complex to keep all the B's in balance. Thorne Research B Complex is good and contains Methylfolate ( natural ) - in place of Folic Acid - ( synthetic ). This combination will assist in the reduction of Homocysteine.

Surely your Doc should know that B12 is water soluble so you cannot overdose - it is just excreted. Now you know why dogs lick their bums :-) They are topping up ! I read this over on the PAS forum and it made me laugh :-) You learn something everyday !!

B12 goes through various stages on its pathway so the various forms seem more effective on different symptoms I have read. I take Hydroxycobalamin injections and orally - Methylcobalamin....

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