Log in
Pernicious Anaemia Society
18,428 members12,646 posts

B12 deficiency myelin sheath

Hi All

Reading the posts on here and reading about b12 deficiency across articles on the internet two consequences of b12 deficiency arise on a regular basis:

1 the increase in red blood cells which appear to be the cause of PA


2 damage to the myelin sheath which appears to cause the problems with the nervous system.

Are both these consequences related to PA or are they separate outcomes caused by b12 deficiency.

I do not have the symptoms commonly stated on here relating to PA but I do have problems with my mental processes which appear to relate to the myelin sheath being damage in my brain.

My symptoms are:

A state of semi consciousness suddenly occurring

Followed by tinnitus

Followed by auditory hallucinations

Followed by a state of confusion.

The incidents last no more than 10 seconds and, over the years of treatment, the tinnitus no longer occurs and the auditory hallucinations have become rare occurrences.

Furthermore, is this process the link with dementia which is stated as a p9tentisl outcome of b12 deficiency?

26 Replies

PA is the somewhat misleading name given to the autoimmune illness whereby the body attacks and destroys gastric parietal cells (which produce acid to help digest protein and intrinsic factor which binds to B12 so that the body can absorb it). As a double whammy the body might also produce antibodies against any intrinsic factor that might be produced.

The result of the above is that the body can no longer absorb vitamin B12 from food or oral supplements. This results in B12 deficiency. PA is not the only cause of B12d, a vegan diet without supplements for example will also cause B12d.

Not everyone with B12d, whatever it’s cause, will suffer anaemia.

Where anaemia and/or damage to the myelin sheath is suffered this is a consequence of the B12d, no matter whether the cause is PA or otherwise.

Regarding your final question about the link to dementia, I’m sorry but I don’t have sufficient knowledge to answer this.

1 like

Thank you, Jan. my b12 deficiency was caused by a near vegan diet plus my doctor prescribing omaprezole for years. Nevertheless, if ones body has been starved of b12 will both PA and damage to the myelin sheath not occur together as a consequence or is it just a Lottery as to which consequence occurs.

Many of the symptoms reported on here seem to have neurological consequences but I am not sure which are caused by enlarged red blood corpuscles and which through damage to the myelin sheath.


There are many and varied symptoms of B12d whether arising through the autoimmune illness called PA or through other causes. I don’t have any scientific backing but it appears to me to be a lottery as to which symptoms any one person gets. I had raised MCV in my blood test, exhaustion and tingling fingers.

I imagine that neurological symptoms are caused by damage to the myelin sheath. But at the end of the day if the cause of the neurological symptoms is B12d (whatever has been the cause of that, autoimmune illness, vegan diet etc) then the treatment is B12 whether you are trying to heal anaemia or the myelin sheath.


Very true, Jan. I understood that reduction in stomach acid was the major cause of b12 deficiency . However, as far as my surgery is concerned, PA is the only consequence of b12 deficiency- when I’ve told them about my symptoms they simply say that I’m the only b12 deficient patient with these symptoms then leave me to suffer them. However, as you say, whatever they think b12 injections are the solution to whichever consequence and, as they are supplying the injections, they are performing their duty of care to me.

It just happens to be a very lonely and worrying place that I inhabit.

1 like

It probably depends on the cause of the b12 deficiency, how your body uses b12 and the other B vitamins and if you were deficient in other nutrients because the megaloblastic anemia caused by b12 deficiency can be masked if there is enough folate (a vitamin which is a lot easier to absorb than b12). Then it appears the neurological symptoms happen at a lot lower levels than megaloblastic anemia which the minimum for the b12 serum test is based on due to another accident of history (the other being Autoimmune Metaplastic Atrophic Gastritis or vitamin b12 deficiency in general, being called pernicious anaemia).


PA is an historic anaemia - it was first observed as a type of anaemia in which red blood cells were larger and rounder than normal, and resulted in in neurological problems, blindness, madness and death - this was a few 100 years before vitamin B12 deficiency was identified as the actual cause.

Anaemia is a consequence of B12 deficiency because B12 is involved in the process that produces new red blood cells. It is also used in a number of critical processes including the process that maintains the myelin sheath around your nerves, the process that recycles neuro transmitters, the process you use to release energy in your cells .... symptoms are caused because your cells don't have enough B12 to run all these processes.


A B12 deficiency that affects the nerves will show first in the nerves of the feet, then the hands. It causes tingling and numbness.

I don't believe there are any cases at all of it affecting only the nerves in the brain.


Thanks for that! I’m in real trouble then!


fbirder, I'm curious as to your source for saying that B12 affects feet first and then the hands. Its not something I've come across before and personally I would say that my hands were affected before my feet were.

I'm also not sure that damage to the myelin sheath is the only way in which B12 deficiency will affect nerve signals as it also appears to be involved in the processes by which neurotransmitters are reset.

It is possible to have neuropsychiatric symptoms separately from symptoms associated with peripheral neuropathy.


Good heavens!

Yes, it seems that one of the ways that PN caused by a lack of B12 can be separated from length-dependent sensorimotor axonal peripheral neuropathies is that B12 causes a sudden onset in both hands and feet, sometimes hands only. ncbi.nlm.nih.gov/pmc/articl...

I never knew that. It’s very annoying that neither of my books on PN mention this. Nor do any of my B12 books.

That must be one of the main reasons why b12 was dismissed as the cause of my neuropathy.

I’ve not seen any evidence that B12 is actively involved in neurotransmitters, a part from the way that it is involved in everything via epigenetics.

From the lots that I’ve read nobody seems to have much more than a guess as to how B12 can cause the neuropsychiatric symptoms.


thank you.


@Alfabeta, you're not necessarily in trouble. I have several articles reporting dementia and cognitive decline associated with B12 deficiency, but no mention of peripheral neuropathy. E.g.


The VITACOG trial run by David Smith at Oxford is investigating associations between B12 and dementia:


David Smith spoke about some of his research at the 2013 PAS conference

his talk starts at 3.30.

I think B12 deficiency is also associated with depression and other mental illnesses.

1 like

This is an interesting video. The speaker mentioned follow up studies - do you know if these were carried out?


I think the VITACOG study has published a few articles. You should be able to find them by searching for VITACOG on pubmed or Google.


There have been subsequent studies and results have been mixed. Certainly not the case that supplementing B12/folate will prevent cognitive decline. More likely that it helps where B12 and folate absorption is part of the problem ... just as supplementing B12 won't make your hair grow back unless B12 deficiency was the reason it was falling out.


Thank you, Gambit, for sharing your vast knowledge. In my case, prior to diagnosis as b12 deficient, I had nominal aphasia and my short term memory was very poor - my partner had to explain what had happened in a previous episode of a tv series as I had little and sometimes no memory of what happened.

Since the injections started (over three years ago) my nominal aphasia has improved dramatically as has my short term memory.

Daily, I am able to see my improvement which suggests that treatment can reverse the mental decline caused by b12 deficiency. At least, I hope this is the case!


What interested me was the images of the brain scans, which visually showed clear improvement following supplementation. The people taking the supplements and showing the necessary improvement to slow progression to Alzheimers (as I understood it) were all within the usual "normal" range for B12.


frodo, the study in 2012 did seem to show that B12 and folate could help but there have been other studies that haven't replicated the results.


Hmm. How odd. I mean the evidence is right there. Maybe the people they tested were too far along or needed injections to make a difference.


back to if B12 deficiency is the problem B12 will resolve the problem - providing it hasn't been left too long - generally that 6 month window that gets referred to in relation to treating the damage.

1 like

Thank you so much for your constructive and informed reply. I am sure, as of yet, that I do not have pa. The very fact that dementia is on the list of outcomes of b12 deficiency must mean that the brain can be affected - is the myelin sheath in the brain?


There is myelin in the brain and spinal cord.


The administrators view stated above is that a b12 deficiency will affect feet then hands first! I had very low b12 in my system but I’ve had no issues with my feet or legs. I’ve had tingling prior to and during my attacks but mostly in the head and the right side of my body. Sometimes my hands tingle.I’m really quite confused about my condition and, as I said above, my surgery knows less than I do!


Hello. My symptoms started with vertigo. My MRI shows damage to the myalin sheath in my brain. I was hardly able to walk. Migraines. Electric waves through head and body. In bed 22hrs out of 24 in a sort of trance . I even went through a and e. It was then a blood test revealed I was b12 defient. I've had tremors muscle aches but only recently had pins and needles occassionly in my legs but more in my right one at night. . So yes your nerves in your brain can be affected first. The control centre. Everyone doesn't seem to follow a certain order of events. Some symptoms seem more common than others. My G.p. didn't think all symptoms were b12 defiency. He thought I was having panic attacks! ! I've made improvements with every other day b12 injections and so far nothing else has been found . I think I must've been low for some time. My first ever b12 serum test was 106. So as we see on here everyone can present with different symptoms . I had trouble getting the frequency of injections as not diagnosed with PA from blood tests. I think it was foggy me that pointed out I should be getting more treatment and Annon and clivalive. Probably more but I was so ill it took a while to get what I now know was obviously needed. I may have pa though as not absorbing b12. Wasn't my diet. I also have had more problrms with my right side which doesn't fit?? So no thanks to G.p and big thanks to the first ever forum I've been on

I wish you well


B12/folate/B6 deficiency can result in lesions appearing in the brain - a lesion is an abnormality that appears on a scan.


The lesions tend to concentrate around the hollow regions of the brain where cerebro-spinal fluids are produced/flow ...

I'm not clear if that means that it is myelin sheath damage or something else that causes the damage.


I too had symptoms in feet at a much later stage. Migraine and brain symptoms first.

However, I believe (but can't prove) I was first severely deficient 30 years ago, and extreme limb weakness was a major issue.


You may also like...