Pernicious Anaemia Society
16,284 members11,339 posts

How much b12 am I meant to be taking

Hi just in early stages of my menopause and have ordered some b12 injections can some one tell me how many 1ml sirgins I meant to be taking as I have already objected 3 in the space of 2 weeks I think it is fantastic and as given me so much energy can I over dose on it and how much can I take my friend told me I can inject every day if need to be

11 Replies

Hi Sa12 without knowing what your Vitamin B12 level was before you started injecting it is difficult to know how deficient you might have been but, if you are feeling so much benefit from one every four or five days then only you can tell how often you "need them".

Your friend is right but when you get to the stage when "there is no further improvement" do maintenance injections every three months.

What sort of diet do you have. Are you vegan/vegetarian?

I am not a medically trained person but there are others on here who can give you good advice.

1 like

Personally I wouldn't have advised using B12 injections if you didn't have an absorption problem - although it isn't toxic high serum B12 levels can cause other problems as the level falls so you may find that, even if you didn't have an absorption problem before - you will need to be injecting for ever - not just during the menopause.

There is no known toxicity from B12 - hydroxocobalamin is used as a treatment of preference for cyanide poisoning as a result of this - administration is 5000x the amount you are taking intravenously over 15 minutes, followed by a second dose if needed 30 minutes later.


That's very interesting Gambit, so if someone doesn't have PA to start with injections create an absorption problem. Does something happen with intrinsic factor?


Gambit62 will have the reference for this but iirc over-supplementation for non-deficient people, and even necessary supplementation for B12-deficient people, will over time saturate the transcobalamin protein which then decreases the capacity to 'download' B12 into the tissues.

So, if people are supplementing when it's not necessary, there's a risk that they will hasten B12 deficiency in the tissues (aka create a functional deficiency).

However, I'll see what Gambit62 says.

1 like

ITYFIALMCTT see explanation below

1 like

hope this explanation also helps you understand.

taking the injection doesn't cause an absorption problem

functional B12 deficiency is a problem with metabolising B12 after it has been absorbed in the gut and is in your blood. functional B12 deficiency doesn't cause PA and doesn't affect Intrinsic factor.

Absorption problems stop you absorbing B12 in the gut, so act as a break on getting B12 in to your blood, which is why serum B12 generally works as a way of seeing if you have an absorption problem. A lot of things can then go wrong once the B12 is in your blood, which is why serum B12 isn't necessarily a good indicator of B12 deficiency. Metabolising B12 is very complex and involves getting it from your blood to your cells and then being able to use it efficiently in your cells for a number of processes and things can go wrong with both of these steps.

Injections by-pass the gut, meaning that B12 gets into your blood through other tissues, so by-passes an absorption problem.

Functional deficiency is the result of something going wrong in the step that transfers B12 from your blood to your cells.

Functional deficiency doesn't occur in everyone but it seems to occur in enough people for it to be a real risk.


Thank you Gambit and ITYFIALMCTT for your explanations. I was aware of functional deficiency in relation to PA, although my understanding of it was rather fuzzy round the edges but had never considered it in relation to non-PA. Does this apply to supplementation with oral B12 or just injections? How would you know you had functional B12 deficiency with injections, is it just very high serum levels or a failure to get relief from the neurological symptoms.

Saturation of the transcobalamin protein does make sense to me, presumably we do not have a finite number to cope with large amounts of B12 over an extended period of time, something our bodies would not, under normal circumstances, be called upon to cope with.

I was reading a while back now that absorption of B12 through the normal route is limited to the amount of intrinsic factor available, but once the intrinsic factor had dealt with the original meal over a period or several hours, it could then go on and cleave the B12 from a subsequent meal - makes me wonder if smaller (say 500ug) more frequent injections might overcome the possibility of saturating the transcobalamin protein.

Thanks again, much appreciated.



functional deficiency is a reaction to high levels of B12 in serum so its totally independent of how the B12 gets there.

this problem doesn't occur in everyone

Cassie, the injections are by passing the gut and the use of intrinsic factor so IF is irrelevant and wouldn't be a factor in deciding the frequency and size of injections. The size and frequency of injections depends more on how quickly you remove B12 from your system.

Not sure there really is any such thing as 'saturation of the transcobalamin protein'.


Thanks Gambit. I think my reference to IF was misleading. I realise injections bypass the gut, but I was referring to people with no absorption problems. IF seems to be a limiting factor in the amount of B12 than can be cleaved at any one B12 meal but would be able to continue to cleave B12 if enough time had elapsed, say several hours. I was just likening this process to the transcobalamin protein and wondered if a similar process could be at work there.

Sorry for the confusion


Ok so I was only taking them on say so!! as been really tied lately and a friend advise me to start taking b12 injections I wasn't aware I could course more problems I haven't been tested for low b12 and not aware that I have any think wrong with me apart from being in my menopause do u think I should continue taking these injections ? All I know is when I've taken it I have lots of energy


as you have started you might as well continue - not toxic and functional B12 can be treated quite efficiently by keeping B12 high - just that you might need to continue with them forever now - the increased energy isn't necessarily a sign you were B12 deficient before, but it could be.


You may also like...