Pernicious Anaemia Society

B12 tablets...Do they work

I have recently be prescribed Cyancobalamin 50 mcg tabs 3 times a day by GP after my b12 level was checked and described as low. The GP suggested this may be caused by poor B12 absorption in my GI tract. My symptoms mainly are Paresthesia in my fingertips and soles of my feet. I am wondering how tablet form of B12 will be absorbed any better as so far I have had no improvement. Would injections be better??

3 Replies

If the suspicion is an absorption problem then the amounts of B12 in the tablets you are being given is unlikely to do anything. Most B12 is absorbed in the ileum - though an estimated 1% is absorbed passively outside the ileum.

RDA for B12 is about 2.4mcg a day for someone who is able to absorb in the ileum. You would be taking about 150mcg a day - which is about 60xRDA.

However, if you are only absorbing 1% of the B12 then the amount you are actually getting is only 1.5mcg a day - ie 60% of RDA

Now, you may still have some absorption in the ileum at the moment - though generally if you have got to the point of deficiency then it's not going to be a significant amount of absorption so you might be getting 1xRDA from that amount.

Recommendation if someone is using oral B12 when there is an absorption problem is an amount of around 1000mcg a day as a minimum - which would equate to around 4xRDA - but that would be after loading doses to build up the amount in your blood first - as a maintenance regime ... and it isn't a recommended/licensed treatment in the UK.

You really do need to go back to your GP and point out that the doses you are going to be getting from the tablets are inadequate if the cause of your B12 problem is absorption - the tablets you are being given are intended to correct a dietary deficiency - for which they should be effective doses.


Thanks for the reply you have confirmed my suspicions. Back to the GP ASAP

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Even the British National Formulary says:

Apart from dietary deficiency, all other causes of vitamin B12 deficiency are attributable to malabsorption. There is little place for the use of low-dose vitamin B12 orally and none for vitamin B12 intrinsic factor complexes given by mouth. Vitamin B12 in larger oral doses of 1–2 mg daily [unlicensed] may be effective.

The only low dose B12 mentioned there is 50 microgram cyanocobalamin with this statement:

By mouth, vitamin B12 deficiency of dietary origin, 50–150 micrograms daily taken between meals;

In my book, there is no support whatsoever for low dose B12 of any sort except in those who have "normal" needs but simply have a diet which is low in B12.


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