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Pernicious Anaemia Society
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Can too much B12 damage the liver?

My next-door neighbor called this afternoon telling me that her doctor won't renew her prescription for her B12 injections. She gives herself shots of 1000 mcg cyanocobalamin weekly, although she said she's missed some shots recently. Her level is high (I believe she said 1200), and her doctor told her too much B12 in the blood will damage her liver. I told her I thought this might be a possibility because the liver has to convert the cyanocobalamin to methylcobalamin. As a side note, I give myself monthly injections of 1000mcg cyano and also supplement daily with 5000 mcg sublingual methyl tablets. I gave her sublingual tablets to take, but she hasn't been doing this lately.

Has anyone else heard that too much B12 can damage the liver? If so, can you point me to sources to back this up?

If you have heard that B12 won't damage the liver, could you point to sources to back up this as well?

Thank you,

Nedi in Texas

17 Replies


The above address is from LiveStrong and references the Mayo Clinic studies. I was told that your body will only keep what it needs and eliminates the remaining. I will believe my Neurologist.


Thank you for that, bebe1964. I too have heard and read many places that the body eliminates excess B12. I will share the Livestrong site with my friend.

I just read your profile. All the best to you in your journey.


As a side note, in the UK injections would almost universally be hydroxocobalamin - and our standards seem to preclude the use of cyanocobalamin for injections.

I am somewhat surprised to see cyanocobalamin being used in this way.



And in UK we are usually not given more than one injection every 12 weeks.



I have injections every 4 weeks.


morning margo... i have resorted to b12 spray now.


Sounds good Pettals, let's hope it does the trick!


well th eway i feel and the way my hair is falling out there is more than just that missing.


I have just convinced my nice GP to let me have them at 8 weeks and there did not seem to be a problem.


Dear Nedi

You appear to be setting great store by the Serum levels that are present in the blood, you make no mention of tests which are needed to ascertain what use your bodies may or may not be able to make of the B12. Firstly I feel it is most important to test your Intrinsic factor and then your Parietal Cell Antibodies. If these come back as NEG then you will need to test the HoloTC levels (Active B12) and then if that is not conclusive you should test your MMA levels, then and only then will you know if you need B12 at all and more over, if your body is making use of the B12 you are taking. Might I respectfully suggest that you talk to experts in the field at Guy's / St Thomas's Hospital in London. Contact :- Denise O'Blein on 0207 188 7188, Guy's have a team of experts working on these problems every day, under Dr. Dominic Harrington who is their Director of Scientific Research, well worth a call simply to put your mind at rest.

Good luck, hope these guys will put your mind at rest.


I have my doubts that Guys would regard people in Texas as being within their remit. :-)


A note to Helvella: in Canada the only source of injectable B12 is cianocobalamin. I have checked this thoroughly with several pharmacists, and the methyl form is only available here in drops, sublingual strips, or pills. For injectable methyl Canadians would have to purchase from US sources. I currently use B12 methyl form spray purchased online from the US.

In addition, and this note is for B12Turbo, the Active B12 test appears not available in North America. I contacted the private lab that offers that testing in UK/Europe and they linked me to their office in the US, that site offers many tests, but not the Active B12. The company in Europe that offers the Holo test has an office in Toronto, but I was not able to convince their sales staff to put me in touch with the labs in Canada that purchase their assay test kits.

I have located online information indicating that only 10 to 30% of the B12 in the blood serum is Active. Any excess B12 the body does not require is excreted. B12 and iron are stored in the liver.


It appears you guys have a problem, sorry Nedi, I hadn't notice in my rush to get out this morning, that you were in Texas. I'm honestly amazed that the HolTC testing is not available state side, surely us Brit's can't be leading the way in matters medical. All I can add, is that as I understand it, if you have blood taken, then get your labs to separate the serum and freeze it, then you would have 3 days or so in order to get the sample to Guy's hospital in London for testing, if that helps. However, I feel it would be well worth a telephone call to Guy's in order to ascertain just what if anything they can do for you by way of a HoloTC test, or try writing to Dr Dominic Harrington at Guy's along those lines, after all, these are private testing facilities for which you have to pay, here in Britain, we are charged £18.00 Sterling for an active B12 test and I can see no reason why they would not do the same for our best buddies State Side. Give it a go, what have you got to loose ???

Good luck

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thank you for this. I have been scowering the USA and outside of the country for a HoloTC test. I sure hope Guy's hospital is still able to help


Taking moderate amounts of B12 isn't going to damage the liver... but the more that you take beyond what you need, then the more work you create for your liver... and that kind of thing is cumulative... if you tax your liver too hard, then it could start to cough and splutter. It's unlikely, but it could happen, as there are all kinds of other jobs that your liver has to do at the same time and you don't really know how it's coping. You never know what might be the straw that breaks the camels back.


I know what you say could well be true for cyanocobalamin, since the liver must convert it to the form the body uses, namely methylcobalamin. The high dose I take is sublingual methylcobalamin, and I can't imagine this could hurt the liver, since that organ is not involved. Any thoughts on that?


If you take something in excess, it still needs to be eliminated, which means liver and/or kidneys... so even if it's not the cyano form, the extra B12 is still creating a little bit more work for your system.

Personally I would take whatever the minimum is to feel well, and keep my numbers in the top third of the range. In my case, Hopefully those would be the same thing... otherwise I would want to investigate further.

I wouldn't want to be over range because that is not necessarily healthier and in fact, might even be associated with worse health. Very high levels of B12 can also be the result of illness rather than the cause of it - but it's hard to see what's going on if you're taking super high levels of supplements. I'm wondering if this doctor has things the wrong way around... because very high levels of B12 could indicate liver problems.


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