Adenosylcobalamin: So far I have had... - Pernicious Anaemi...

Pernicious Anaemia Society
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So far I have had shots of cyano, hydroxo and methyl forms of cobalamin. Methyl felt the best both in terms of fewest symptoms after shot and feeling of well being. So it seems to make sense to go with that. But I understand that we also need the adenosyl form of b12 which we get when our body converts cyano or hydroxo. If I go with methyl shots will I become deficient in adenosyl form of b12? Or do we need less of that so I could just supplement with sublinguals or nasal spray (if I can find such things - they mostly seem to be methyl)?

15 Replies

Once they enter the cell all forms of B12 are identical. The first thing that happens is that the top ligand (methyl, cyano, hydroxo, adenosyl) is removed to form cobal(II)amin.

If you take methylcobalamin then it is converted to cobal(II)amin which is hen transported to the correct regions of the cell where it is converted to methylcobalamin or adenosylcobalamin as needed.

Thank you, I have only recently been diagnosed, and wondered if all forms of VitB12 were the same within the body, so glad for this post.

You only need injections of B12 if you have absorbtion problems for whatever reason -the most common being Pernicious Anaemia . You are benefitting so well from Methylcobalamin, you do not need Adenosylcobalamin , as the Methylcobalamin will convert to it as necessary . It is obtainable as an injection , but is very unstable and expensive and not necessary . Not obtainable in tablet form.

For most people Hydroxocobalamin injections are ideal .


I have PA and have prescribed injections every 10 weeks, I feel well, occasional tingling in big toe but it's not an issue. I also buy slow release VitB12 tablets 1000mg, as I want to keep my stock high, since I'm well. My GP is ok with this so long as I stop taking them prior to blood checks. I'm just wondering your view on this and if I'm doing the right thing, and quite newly diagnoses. Many thanks

Well if you have PA , it’s unlikely that B12 tablets will be of benefit , as PA patients cannot absorb B12 in the gut . ( That’s why you have injections ) The tablets will succeed in raising your B12 blood serum level though , but B12 will not get through into your cells . If you feel you need more B12 because symptoms return before your injection is due,then the answer is more frequent injections. Once you have been diagnosed with PA , and receive injections , blood tests are superfluous .

Very best wishes .

Thank you. Another wee question, when I read about the slow release tablets it said that they were absorbed in the small bowel not the stomach, so in theory bypassed the intrinsic issue. When you refer yo the 'gut' do you mean stomach or bowel? As a U.K. Nurse it's not a word I use, many thanks Wedgewood x

Here is a link to a paper that describes the rates of use and absorption among general population vs those with pernicious anemia due to intrinsic factor issues. It's from 2008. I found it interesting and thoughtful. Not sure if it has been discussed on this forum.

Thank you very much, I'll have a read this evening x

in reply to topher2018

The oral absorption data used for that is over 50 years old. I’m not sure how much credence I would give it.

in reply to Miss-guineapig

Hi Miss-guineapig. Just to add to wedgewood's comments...

Many GPs insist on continuing to test serum B12 levels following the commencement of treatment. This is wrong since B12 levels should be high, following injections - sometimes off the top of the reference range. All the guidelines state that testing is not required once injections have started (unless checking for low levels of B12). Also be aware that GPs sometimes stop B12 treatment when levels come back at sometimes astronomical levels following injections. This is also wrong since B12 levels following injections are no indicator as to the efficacy of treatment - GP should look at symptoms, not serum (or active) B12 levels.

And just a thought about your tingling toe...thismis a neurolgical symptom and if you have neurolgical symptoms your GP should have prescribed a more intensive treatment regime. After the six loading doses, injections should continue every other day until no further improvement (see the BNF for details of the neurological treatment regime - about third paragraph down - doctors rarely read that far down and many have never heard of this).

Getting the right treatment in the early stages is crucial for optimal recovery, especially where neurological symptoms are concerned.

Whilst some people use high dose sublinguals or tablets to supplement between injections, they don't work for many (most) people with PA - they tend to get used out of desperation because we are under-treated - GPs will not prescribe frequent enough injections for we deficients to get and stay well. And in the UK, the only recommended treatment for those with neurological symptoms is B12 injections.

I'm going to paste in a few links that will give you more information about the above (just to start you off 😉):

b12researchgroup.wordpress.... (Serious Caution Note about the use of Oral and Sublingual B12 Supplements)

(BNF B12 Deficiency: Hydroxocobalamin Treatment Regimes) (Problems with Serum B12 Test) (Testing B12 During Treatment) (Misconceptions About B12 Deficiency – Good to Know Before Seeing GP) (B12 Treatment Safety / Long Term Treatment for neurological symptoms)

If you look to the left of the page when you log on (or at the bottom, if using a phone), you'll see a section called pinned posts. The second and third PAS pinned posts contain more information that you'll find interesting - and perhaps essential if your GP does not understand B12 deficiency / PA very well - which I suspect may be the case in light of his desire to re-test B12 levels and his agreement for you to use oral supplements rather than treat your deficIency adequately.

PA and B12 deficIency can be very complex so do post again if you have any more questions...or just want to pop in for a chat.

Good luck


Brilliant, thank you so very much. X


extremely unlikely to the point of zero probability

- though there has been a reported case of one person who wasn't able to convert adenosyl to methyl - a rare genetic condition.

Well , I have obviously looked into the B12 question in detail . I didn’t know that you were a nurse , so I used a word that can be understood universally . It is possible for 1% of B12 intake to be absorbed in the ileum which is part of the small bowel . But this is of no interest if you really suffer from P.A.

PA patients would be prescribed these tablets by their GPs if they were really effective .

Many thanks indeed, I just have an awareness re PA but no real knowledge as it's not my field. I suppose I thought a reasonable percentage would have been absorbed in the ileum. Just goes to show! X

It is my understanding that if you do shots of methyl B12 then adding in a sublingual of adenosyl completes the pathway. I got this info from the FB PA site.

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