A study has shown that taking high dose oral B12 doesn’t result in higher blood levels than those on low dose oral B12.
That sort of puts the kibosh on the idea of passive absorption. If a 1000 mcg oral dose gives the same blood levels as a 10 mcg oral dose then only 10 mcg, or less, can be getting absorbed from the 1000 mcg dose.
I take oral B12 and noticed a huge improvement when I upped my daily amount. Did the people tested have PA or B12D? In normal people the body excretes excess vitamin B12.
They restate/describe passive absorption in the introduction:
"Approximately 1% of vitamin B-12 at supraphysiologic doses ≥100 μ g of crystalline vitamin B-12 can be absorbed independent of intrinsic factor–mediated transport "
I think the study just indicates, that in the general population with working intrinsic factor absorption, 25mcg of supplemental B12 is adequate and taking even 1,000mcg daily doses instead does not improve B12 status versus 25mcg. Interestingly, in one age group, between 25 and 100mcg was most effective - 100mcg happens to be what I take.
It's not so much a refutation of passive absorption so much as indicating that quite small supplemental doses of B12 (10-25mcg) are more than adequate in a healthy general population, and supra-physiologic doses like 1000mcg have no real advantage - the body likely removes the excess pretty quickly.
It doesn't tell us anything about the effectiveness or adequacy of oral B12 in those with PA.
> It doesn't tell us anything about the effectiveness or adequacy of oral B12 in those with PA
Indeed. Or those with other causes of B12 malabsorption. I don't have PA but had my terminal ileum surgically removed (Crohn's Disease) 50 years ago. I was on 3-monthly B12 jabs for decades until I started experimenting with oral B12 a few years ago. Several oral 1mg (1000ug) tabs per day keep my serum B12 levels high, but smaller doses result in a steadily decreasing level over a period of weeks/months until the onset of symptoms and serum B12 levels below the normal range.
I have been trying to ask this question for a while...if only 1% of what we take in is absorbed, why take a 1000 mcg. injection? I happen to inject every two weeks. Technoid, do you self-inject and/or take 100 mcg. oral B12 daily. I am wondering how 1 mg./injection became the standard if this is true. Seems like I may be better off injecting less more often? Or is there something I still don't understand? I do believe I need to inject, as oral doses did not do anything for me. I would rather not inject more often than I have to because of the cost, hassle of doing it daily.
Well, I don't have PA or absorption issues so 100mcg daily is quite enough for me.
I'm not really sure why 1000mcg is the amount used in B12 injections but it may be related to the idea of providing an excess that would replete B12 stores. In terms of injections, I have theorized that smaller doses taken more frequently may be more effective than large doses, taken infrequently but I have not heard of this being experimentally tested so I don't know if it would work or not.
Remember that the 1% passive absorption figure only applies to oral B12, it is not relevant to injections.
I think you are making the wrong conclusions here. The first thing is that this study is being done on people who do not have PA. They can get adequate B12 from very low doses because their B12 intake system is not broken like ours is. People pee out extra B12. The problem with people with PA is that only a tiny amount of the huge dose of B12 is absorbed because of the lack of intrinsic factor. If for example, someone only absorbs 1%, then 1000mcg only gives them 10mcg. Over time, some of us (like me who could initially take supplements) can stop absorbing enough even from the massive doses.
You say: If a 1000 mcg oral dose gives the same blood levels as a 10 mcg oral dose then only 10 mcg, or less, can be getting absorbed from the 1000 mcg dose.
But another explanation is that healthy people absorb a lot of the 1000 mcg dose then pee out all but the tiny bit that their bodies actually need. People with PA will absorb very little from that dose. If someone with PA can absorb 10mcg of it, you can subsist on daily 1000mcg supplements. Otherwise, the person probably needs injected B12. We pee out a huge amount of our injected B12 as well, but at least enough of it gets into our bodies so that it can be used where it is needed.
Thanks for posting, Artemisfowl.
A few notes:
Some years ago, I remember seeing that it required doses of at least 500 micrograms, maybe 750 micrograms, to see an increase in absorption that could be due to diffusion or some other process that was not intrinsic factor mediated.
If that is the case, then those taking between 100 and somewhere around 500 to 750 might not absorb any more B12.
Those taking the top end - 750- to 1000 - might experience increase absorption.
A pity that the study did not have more dosage bands which might have helped to demonstrate that - or not.
I wonder how many of those taking the highest doses do so because they have noticed a difference? Although I no longer experience anything I can attribute to my daily 1000 B12 dose, when I first started, I did believe that they had a direct effect for at least many months, possibly years.
If I had never felt a difference, perhaps I’d content myself with low dose - whether as B12 or just one of the ingredients in some sort of combination.
That could imply that at least some of those on high doses are a self-selecting and very much non-random subset.
It is also a great pity that they didn’t perform both serum and Active B12 tests in all subjects.
I have always thought that oral B12 might be affected by whether we take it near a meal, and what that meal was.
For one obvious example, any food which contains a cyanide compound might well bind to hydroxo- or methyl-cobalamin.
The study also doesn’t mention smoking - or not.
The study doesn’t appear to consider the different forms of cobalamin.
Oral contraceptive and b12 deficiency - how much can it reduce levels? 
high levels of B12 in blood
B12 low told to start oral treatment 
High levels of b12!!!
Blood test waiting period after taking high strength B12 sub-lingually for a couple of years?
