Why low B12 is associated with autoimmune thyroiditis

Many people with autoimmune thyroiditis also have antibodies against the parietal cells that make up part of their stomachs.

The effects of having these antibodies can include a reduction in the ability to absorb vitamin B12 from food. (The parietal cells produce intrinsic factor which is crucial to normal absorption of B12. When attacked by antibodies they cannot produce enough.) This is why it might be necessary to supplement with B12 even if you are on a good diet which ordinarily would provide plenty. Typically oral supplementation with 1000 mcg methylcobalamin is used - with such a large dose you absorb it even without intrinsic factor.

Testing for B12 is desirable (and fairly readily available) but, as so often, the reference range is often argued over.

Human bodies can store enough B12 to last for several years - so you could have an acceptable B12 level when first tested and only slowly worsen. So don't rely on "I was tested for that at the beginning".

The abstract below suggests that at referral around 30% of patients had these antibodies.

Prevalence of Parietal Cell Antibodies in a Large Cohort of Patients with Autoimmune Thyroiditis.

Checchi S, Montanaro A, Ciuoli C, Brusco L, Pasqui L, Fioravanti C, Sestini F, Pacini F.

Section of Endocrinology and Metabolism, Department of Internal Medicine, Endocrinology and Metabolism and Biochemistry, University of Siena , Siena, Italy .


Background: Autoimmune thyroiditis (AIT) may be associated with other organ-specific autoimmune disorders, including autoimmune gastritis, but the prevalence of this association is not entirely quantified. The aim of this study was to investigate the prevalence of parietal cell antibodies (PCA) in a large cohort of consecutive patients with AIT. Methods: We retrospectively studied 2016 consecutive women and 258 men with AIT seen at our referral center in the period from 2004 to 2008. All patients were screened for the presence of PCA in the serum.

Results: The prevalence of serum PCA in female patients was 29.7% and progressively increased from 13% in the first-second decade of life to peak at 42% in the ninth decade. During follow up, 21.1% of the PCA-positive patients converted to PCA-negative status. Mean (±standard deviation) basal PCA levels in this group were significantly lower (32?±?28?U/mL) compared with those remaining PCA positive (129?±?200?U/mL). A similar prevalence (29.8%) with a similar age-dependency was found in male patients.

Conclusions: In conclusion, our study demonstrates a high, age-dependent prevalence of PCA in an unselected large population of patients with AIT.


17 Replies

  • Good post. This is interesting as I know many people with Coeliac Disease (also have low B12 or Pernicious Anemia). As you probably know there is almost a threefold link between autoimmune Thyroid and Coeliac Disease (also autoimmune). As my close relatives have both been diagnosed with Pernicious Anemia and Auto-Immune Thyroid (Hashimotos) I'll be keeping a close eye on B12 and Thyroid tests. Feel free to join the Gluten Free Guerrillas group on here too. We suspect we have some members with Thyroid problems as well and we're happy to cross share info across groups.

  • So many people haven't heard of vit B12, there should be better awareness. Can I just add that to supplement, we need the sublingual B12. I have been supplementing for a couple of years. My last B12 result was over 1,000 which is a significant improvement from the 300 that it was. I have read that it should be more than 500 ideally.

    BBC Inside Out made a documentary a couple of years ago that is available on youtube and really interesting.

  • This is an excellent blog, thank you for posting it

  • Good post, B12 deficiency needs more awareness. I was finally diagnosed with it after having had a diagnosis of m.e. for over eight years. My b12 levels had never been tested in this time, which I consider an absolute disgrace. Since the diagnosis I had loading injections and then one injection every three months. This helped my brain fog and my lower leg bone pain enormously. One injection every three months is not enough though so I bought my own injections and inject myself now, started off daily and now once a week.

    Everybody with fatigue symptoms should be tested, and treated if low. Ask for the result, if below 500 treat yourself with sublingual B12, the doctors will not treat you unless it is below 200, or 180 in some cases!

  • Just seen your response Lizsam.

    Your response makes interesting reading as I was told by my GP that my Vitamin B12 levels were fine at 363 (180-900) but I am very shocked to learn that the doctors will not treat you unless it's much lower than mine! Major shock!

    Jo xxx

  • So sad to see nothing has changed! My doc refuses to even test for it! I have AIT and I also have various gastric problems I am endeavouring to deal with - yup I supplement with sublingual methylcobalamin - I truly wish you well.

  • Hi damehypo, thanks for your reply.

    So sorry to hear you have gastric problems. I have constipation and inability to gain weight. What dose of sublingual methylcobalamin do you take, out of interest? I take 3000IU but have heard there are higher doses out there than that.

    Jo xxx

  • Hi Jo I take 5000mcg (don't ask me what that is in IUs arghhh) the ones I take are made by a company called NOW and called methyl-B12 includes folic acid. Cannot be more help than that sorry - other than take them on an empty stomach away from any other meds or supplements especially vitC

  • Hi Damehypo!! Thanks for your reply.

    It's good that you take a high dose in mcg (I don't know what that is in IU so that makes two of us LOL) And the fact that it includes folic acid is good too.

    Thanks for your answer, you've helped lots. Good luck!! :) I need all the luck I can get with mine as I am to restart it as well as restarting my Levo!

    Jo xxx

  • You are very welcome Jo and I wish you well with it all, especially re=starting levo!

  • I don't think I have ever seen B12 measured in International Units - it seems almost always to be micrograms (occasionally milligrams).

    Could that be 3000 mcg? :-)


  • Oops, my bad. Sorry! It's because I am taking Vitamin B12 at 1000mcg and Vitamin D at 3000IU. I can't believe I did that! Thanks for pointing it out Rod!!

    Feel daft now. :)

    Jo xxx

  • :-)

  • Jo - 5000mcg = 5mg Hope this helps? and as far as converting to IUs is concerned:


  • Hi damehypo, thanks for your reply.

    Sorry, I was getting mixed up. I take Vitamin D as well as Vitamin B12 and I accidentally put the international units with the Vitamin B12! My bad! :)

    Thanks for the link - I will bookmark it for safekeeping. Thank you for finding this out for me. :)

    Jo xxx

  • Is it just Folic Acid you need to take with B12 or all the others? So when you take it sublingual, does that mean you have to take the others via pills?

    And i thought the body can not store B vitamins?

  • The difficulty with B12 is that the mechanisms by which it can be absorbed are complicated and very specific. You could be able to absorb everything else from your gut perfectly well - but not B12. More or less, that is the point about Pernicious Anaemia.

    To have loads of B12 (through injection, tablet, or any other form) but insufficient other B vitamins is possible - but it is also perfectly possible to be deficient only in B12.

    The important thing is that everything ends up in appropriate amounts! And that you do not have plenty of folate but inadequate B12 - that is a recipe for problems because the folate can mask some of the signs of low B12 - but allow other aspects to worsen and cause permanent damage.


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