Pernicious Anaemia Society
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to inject or not to inject?

Hi guys, could you answer a question for me please? I have zero intrinsic factor and am receiving my B12 injections on an 8 week cycle, not enough so am looking towards self injecting at some stage fairly soon, if I can't persuade my GP to be more accomodating. I have read conflicting advice, that sublingual IS effective and that it ISN'T. Which is right?

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I really can't comment other than to say that 1mg of injectable B12 compared to say 5000 mcg of sublingual means that you would have to suck 200 tablets to equal 1mg injection or 1000 tablets if you only use 1000 mcg tablets - always assuming that you absorb the full dose. Would you also want to suck that many tablets?

The cost of sublingual compared to injectable is quite enormous if you think of it that way. Could you afford to pay say £60 or so per month for the 5000 mc compared to a £1 or so for injectable?

Or is my maths and thinking completely wrong here? I do admit that my brains is royally screwed at the moment so may not be thinking logically at all.


Heaven only knows, but I'm not doing the maths!

Short answer is that only 1% of a product taken orally will be absorbed and that is done by a process called passive diffusion.

In some people it works and in others it doesn't.

Got the feeling it's something to do with the way the cells angle or something - doesn't matter - bottom line is that at best you only actually absorb a very small proportion and at worst it might not work at all.


It's nothing to do with the angle of the cells although Kevin Byrne describes it as a gradient. The walls of the receptor cells are porous enough for B12 molecules to pass through so if the level of B12 in the gut is higher than the level in the cells then B12 will be absorbed. Unfortunately, just like water finding its own level, if the level of B12 in the gut falls below the level in the receptor cells then the B12 will go back the other way i.e. it will pass back out of the cells into the gut again and will be wasted.

It's actually more complicated than that but I think that's the basic principle.

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Thank you!

That's actually a damn good explanation.

I was getting angles and gradients mixed up (working, and lots of words in my head) but the upshot is that if you are completely void of B12 it seems to work. Once you have some B12 in your system then the passive diffusion method becomes more difficult.

But you are putting it much better than me...

In my case, I used the oral tabs and they started working within 2 hours. I don't care who doesn't believe me, not interested in proving it anymore, but my eyesight improved - as in I could actually look at something without my eyes running - for example words on a page. But at that stage I actually think I was left with little or no B12. It took 6,000mgs to get my levels up to 178. So go figure what it was before the 6,000mgs.

But when I took the same tablets 3 years later, after I had been injecting, they had no effect whatsoever. And that was because, as you rightly state, there was 'resistance' as the cells already had B12 in them. They weren't receptive to the oral b12. Whereas 3 years previously there was no resistance whatsoever. It was 'Let it through! Gimme, gimme, gimme!'


Your maths is completely wrong. 1000mcg = 1mg.


I did say that my brain was completely screwed, and it is all the computer's fault as it is playing tricks on me the the converters.

Thank you for putting me right.


mg = milli gramme = divide by gramme by 1,000

mcg= micro gramme = divide by gramme by 1,000,000

so as Engels says = 1mg = 1000 micrograms

so one 5mcg tablet contains 5mg so in theory you should need less - but that's only if it is all absorbed. Theory with Sublinguals is that some should be absorbed through membranes in the mouth so it isn't entirely going orally - but I can't comment on how efficient that means of absorption actually is and it will probably vary a lot from person to person even if the tablet is being 'sucked' in the same way.

I would imagine that the effect Engels (sounds like osmosis is involved) describes in terms of absorption of B12 in the gut - or not - will also apply to other membranes so if you have high levels of B12 in your cells from a B12 shot then absorption isn't going to be as efficient.


I recommend you start self inject as soon as possible. You don't have to inform your GP that you are doing this as it's completely legal. I recommend using

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Nobody can actually say sublinguals are effective or they aren't because we are all individuals and our bodies respond in different ways. There is a huge amount of variation in the way people respond to B12 - sublinguals will work for some people - nasal sprays certainly work for me - but injecting is obviously going to be the most efficient way of getting B12 onto the inside of your body.


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