Pernicious Anaemia Society
14,151 members10,146 posts

Oral B12 is useless in some people

"We discuss the management of patients who present with neurological manifestations of vitamin B12deficiency; highlighting the fact that parenteral replacement is needed in such cases, even if the serum vitamin B12level appears to be normal. We also discuss ancillary investigations that should be performed in patients with suspected vitamin B12deficiency."

7 Replies

Thanks for that fbirder . Another bit of evidence to add to my file !

1 like

They don't say FB, but I think they must be talking about oral Cyanocobalamin, which is usually prescribed by the NHS.

Oral methylcobalamin works very well for many people.

This is part of a letter from Wilhelmina Reitsema in 'Rapid responses' to the BMJ research document - see her last paragraph - "Is it important which form is used ....."

" There are two active forms of the B12 enzyme in the human cell. First, Methylcobalamin acts as a co-enzyme for the conversion of homocysteine to methionine. Methionine then acts as a methyl-donor to a great number of reactions that need a methyl group, including the synthesis of myelin, serotonin, dopamine, noradrenalin, DNA and phospholipids...."

"Is it important which form is used in treatment? In most people, it does not matter. They can convert cyano- and hydroxo-cobalamin into the active forms needed. However, I have recently reported a case in which it did matter. The severe vitamin B12 deficiency, including dementia and psychosis, responded to treatment with high dose oral methylcobalamin, but not to equally high dose oral hydroxocobalamin. [1]

1. Rietsema WJ. Unexpected Recovery of Moderate Cognitive Impairment on Treatment with Oral Methylcobalamin. Journal of the American Geriatrics Society 2014;62(8):1611-12 doi: 10.1111/jgs.12966[published Online First: Epub Date]|. "


Those were very interesting to read, thank you. 

This comment from Eddie Vos really nags at me: "just about anyone ingesting 100 mcg/d for some months will absorb sufficient B12 to take care of any known biological, age or genetic impediment."

If that is true, then there would never be a need for injections, would there?

It seems in direct opposition to Erlund Aasheim's response pointing out that:

"Gastric bypass may lead to malabsorption of vitamin B12 for several reasons, including: poor digestion of protein-bound vitamin B12 due to achlorhydria and rapid intestinal transit,5 inadequate secretion of intrinsic factor from parietal cells,6 and proteolysis of intrinsic factor (before it binds B12) by pepsin and trypsin.7

This may explain why 80% of 137 patients developed low cobalamin concentrations in the first 2 years after gastric bypass surgery, despite daily supplementation with multivitamins containing vitamin B12.8

The good news is that vitamin B12 deficiency after gastric bypass is readily preventable...prospective studies show that serum cobalamin concentrations are maintained or increased if patients receive regular parenteral supplementation with B12 after surgery.10"

1 like

I agree Allyson - I prefer to listen to Sally Pachlok and Dr Stuart, ("Could it be B12?"), who would say 100mcg. is not enough if someone is deficient.  They see the tragic results of long term non absorption of B12 every day, working as they do on the front line of emergency medicine in a large city hospital. 

The information on gastric bypass surgery affecting absorption is in all the research and guidelines but many GPs still don't know this.


Right- 100mcg daily for months might serve for a generally healthy person, but that assertion seems in direct conflict with the needs of people with health conditions.

I'm positive my diet was rich in b12, but I still got very sick.

Or is 100mcg/day really sufficient for PA, if given by injection?

1 like

It seems that this 100ug per day myth comes from the idea that even people with PA absorb 1% of the B12 they eat. I'm not sure where this comes from, but it will vary enormously - depending on what else you consume, the amount of acid in your stomach, your gut transfer time, etc., etc.

If you were to inject 100ug a day then I'm sure that would be plenty for the vast majority. But I think I'd rather have one injection every 10 days rather than one a day.

1 like

I seem to not do so steadily on 10 day injections, I think I'd rather have small amounts of daily b12. I'm not sure that 100mcg would be enough, though.

1 like

You may also like...