B12 Injections vs Transdermal vs Lozenges

aaron_c

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I've recently been exploring some B12 deficiency groups, and one thing I've seen reported by members and also one good friend of mine is that sometimes B12 injections help where lozenges do not. (I'm not saying this will be true for all of us, but it makes me curious about whether we can rule out B12 issues without doing injections).

But my question here is how to square that with what I understand to be the case regarding B12 lozenges: That they do increase serum B12. I say this both from a vague recollection of what people here said over a decade ago and also from https://perniciousanemia.org/b12/levels/ which theorizes that the reason normal serum cobalamin doesn't rule out a positive response to cobalamin injections is that you could have a high proportion of your serum cobalamin in a somewhat unusable form (in other words not bound to transcobalamin II but bound to haptocorrin or...I can't tell what transcobalamin III is but bound to that).

So I have some pieces that I can start to put together: It seems like maybe in some people with normal serum B12 who nonetheless respond to B12 injections the problem was (partly?) that much of their serum B12 was still bound to haptocorrin, which according to wikipedia initially gets a chance to bind to B12 in the mouth where it can subsequently protect the B12 from degradation in the stomach. After that it's normally broken down by pancreatic enzymes. Or some of it is, I'm not clear on how much. And then the free B12 is bound to Intrinsic Factor so it can be absorbed in the ilium.

To me this looks like maybe people with problems producing pancreatic enzymes (and I think that's most of us in the chronic illness community?) would then have trouble separating cobalamin from haptocorrin and so perhaps we'd wind up with a higher-than-normal amount of haptocorrin/cobalamin in the blood? And that that might explain why some people benefit from injections over lozenges.

But that's a theory based on pretty thin evidence. Now the questions that I hope yall might have ideas on:

-What is transcobalamin III?
-What is the function of haptocorrin (aka transcobalamin I) when it's in the blood?
-Do folks have experience with B12 injectables? (I know there's a thread on transdermal and I'm interested in that, but I didn't find a good thread on injectables)
-If you do believe that B12 injections work for some people where lozenges fail...what is your explanation for that? Does it explain (or do you dispute) the poor reliability of the serum cobalamin tests? I'm truly asking.

Thanks!
 

aaron_c

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PS To be clear I don't want to sound like I'm thinking "oh I found the solution, everyone just has to inject B12 instead of take lozenges." If that were the case for all of us I think we'd know it by now. So I suspect that IF cobalamin dysfunction is a common part of our illness then there will be more pieces than just this, perhaps an issue with the transcobalamin II receptor or something.