Pernicious Anaemia Society
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Seeking advice on Adenosylcobalamin for P.A

Hi all,

Not sure if this subject has been brought up before - I couldn't find it but apologies if it has. 

During the course of reading about Pernicious Anaemia, I came across the following study which essentially says that methylcobalamin is not on its own an adequate source of B12 replacement therapy as it can't be broken down into adenosylcobalamin - another vital molecule needed for B12 absorption...

Many other sources and studies don't appear to mention this, which has left me confused...

The licensed injections in the UK are usually of the hydroxocobalamin variety, and in the US I understand they're cyanocobalamin. Both these forms, unlike methylcobalamin, can be broken down into adenosylcobalamin, or so it is claimed... (although they are not as 'bioavailable' as the methyl form). 

So if people like myself, with the IF and/or PC antibodies, or for any other reason, are unable to absorb (presumably all forms of) B12 gastrointestinally, where does that leave us with respect to adenosylcobalamin? 

I am not a medic or a biochemist so I'm hoping I've just made a layman's misinterpretation of what is a very complex area, but any views or advice on the matter would be greatly appreciated. 

Many thanks, Doug

9 Replies

I've found a couple of Google hits suggesting that methylcobalamin cannot be converted to adenosylcobalamin, but only from people trying to sell the latter. Can't find any proper scientific papers. The abstract to which you link doesn't actually state that the conversion isn't possible.

I have found stuff that says hydroxocobalamin can be easily converted to both active forms.

I'll have a proper search when I'm back on a proper computer.


i have been wondering recently if there it was possible for the body to convert methyl to adenosyl and vice-versa - not being a biochemist don't know what the chemical relationship is between the two so will be interesting to know.

if i understand things correctly then the two operate with different processes in the body - methyl being good for myelinisation (maintaining the protective layer around nerve cells and adenosyl for energy release in muscle - so just having one form isn't going to be enough if the two can't be converted.

I've come across one study related to diabetic neuropathy which involved using both methyl and adenosyl - though haven't been able to find the article but did come across this

I haven't looked at the whole article just the abstract - but it does rather imply that adenosyl and methyl are forms that the body isn't able to convert so both are needed - either by supplementing both or by using hydroxo or cyanocobalamin which can be converted to either form

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Thing that started me thinking about whether one converts to the other is having observed in the past that methyl does absolutely nothing for my mood whereas when I started taking adenosyl sublingually I did notice feeling calmer.  Haven't had much success in the past hour looking at why adenosyl might be more beneficial psychologically but will keep looking.

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This is one of the articles referred to in the abstract

API = Association of Physicians of India

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I've always wondered whether an inability to convert from methyl to adenosyl was the reason why methyl sublinguals did absolutely nothing for me at all. My main symptoms at the time were fatigue and lack of concentration.

I haven't got time to do the research at the moment so I stand to be corrected but from all the reading I did nearly 10 years ago now I seem to recall that B12 in food is mainly hydroxo and adenosyl. Also, most of the B12 stored in the liver is adenosyl. I've never understood the obsession with methyl either.


The Wikipedia entry for methylcobalamin says it can't be converted into adenosylcobalamin and that methyl should not be used on its own to correct B12 deficiency but should be used in conjunction with adenosyl. Alternatively, just use cyano or hydroxo. Usual Wikipedia caveats apply.

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Thanks for the replies and links. 

It would appear that the adenosyl injections are virtually non-existent, although they can be acquired as oral or sublingual supplements. So... 

1. It appears that humans need both the methyl and adenosyl at a cellular level

2.  We think that the body may not be able to convert MeCbl to Adcbl. 

Perhaps further confirmation of (2) needed - none of us are true specialists after all. For what it's worth I have since asked a relative who is a retired biochemist of 40 years, and my GP, and neither of them were able to offer any insight into the question. 

Martyn H's latest book (which is an excellent synthesis on B12d and PA) also admits that there is much the research community doesn't know about what happens to B12 at a cellular level, and adenosylcobalamin is a particularly mysterious subject. Worrying perhaps as it is also thought to be a vital nutrient for cellular function. 

If I unturn any further information on the subject I will post it here. 

Thanks, D

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The only source of injectable adenosyl that I have come across is Arnika Apotheke in Germany (Munich?). I don't think they list it anywhere on their web site but will supply to order. That was the situation a couple of years ago anyway. Try emailing


Thanks Engels that's really useful.


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