Vitamin B12 – Critically Important but Often Not Diagnosed or Treated Correctly

Vitamin B12, also known as Cobalamin, is a critical and very complex essential vitamin within the human body. It has to be absorbed from food, as we cannot manufacture it ourselves.

I became interested in B12, as low B12 it seems to affect many thyroid patients. This might be due to the fact that low B12, makes T4 to T3 conversion worse. However, low thyroid hormone is likely to make the absorption of B12 from food or supplements less effective.

Moreover, thyroid disease is often caused by autoimmune disease (Hashimoto’s thyroiditis). We know that where there is one autoimmune disease, others can be present. Low B12 can be caused due to an autoimmune condition in some people.

Anyway, let me discuss B12 in more detail, and why it is so important to investigate it properly.

B12 is used in the process of making good quality red blood cells. If B12 is too low, we cannot make the quality of red blood cells needed to carry oxygen around in the body. Sometimes, it affects the number of red blood cells produced and it can cause the ones that are made to die off early. Red blood cells are cycled within the body every 3-4 months, but they can die off and be recycled far sooner if B12 is low.

Low B12 often results in a condition known as anaemia.

Anaemia is the most common disorder of the blood. It is caused by either a low, or below-average number of red blood cells in the blood or less than the normal amount of haemoglobin in the blood. If a patient has a normal number of red blood cells, but they have lower than normal haemoglobin, the patient is usually diagnosed as having iron deficiency anaemia, as iron is used to make haemoglobin. Low iron can therefore impact the ability to carry oxygen around because the oxygen is carried in haemoglobin. Iron deficiency anaemia is often detected by low haemoglobin in a Full Blood Count (FBC).

As mentioned above, low B12 can impact the quality and the number of red blood cells, as it is needed to make them in the bone marrow. Low B12 may be present with, or without Pernicious Anaemia, which is an autoimmune condition where the body attacks itself, and cannot make enough Intrinsic Factor in the stomach. Intrinsic Factor is essential in order for the B12 to be absorbed in the small intestine (in the ileum – the last stage of the small intestine).

There are at least two types of autoantibodies that can cause Pernicious Anaemia. One type, Anti-Intrinsic Factor Antibodies, attack the intrinsic factor itself. The other type, Parietal Cell Antibodies, attack the parietal cells in the stomach that make the intrinsic factor (and parietal cells also make our stomach acid). Anything that disrupts the parietal cells can also reduce the level of intrinsic factor, e.g. Helicobacter Pylori bacteria.

When B12 deficiency is severe it can reduce the number of red blood cells in the body, resulting in low red blood cell count (RBC).  Very low B12 can also cause red blood cells to enlarge and be less effective in carrying oxygen. This can be measured by the mean corpuscular volume (MCV). Both RBC and MCV are also present in an FBC, but there are problems with detecting low B12 that I will discuss in this post.

I have just been reading Martyn Hooper’s excellent book: What you Need to Know About Pernicious Anaemia and Vitamin B12 Deficiency. I was prompted to write this, as I have just read that research has shown that there is an approximately 40% prevalence of B12 deficiency in hypothyroid patients! This is staggeringly high! Whether this is because many hypothyroid patients have the autoimmune condition Hashimoto’s thyroiditis, and pernicious anaemia is another autoimmune condition I do not know.

The above appears to suggest that diagnosing and treating B12 ought to be straightforward.

However, the diagnosis and treatment of low B12 in all its forms is far from straightforward.

Let me give a brief summary of some of the numerous symptoms of B12 deficiency:

  • Tiredness / Fatigue
  • Shortness of breath.
  • Inability to do exercise like you once did.
  • Brain fog / confusion / memory problems.
  • Headaches.
  • Heart palpitations.
  • Pins & needles / numbness  (esp. legs/feet) / nerve damage (can be permanent).
  • Worst case with pernicious anaemia and very low B12 – spinal cord damage, brain lesions and serious nerve damage.
  • Balance / coordination / changes in the way you move / clumsiness.
  • Hair loss.
  • Mood changes / irritability.
  • Sore mouth/ sore tongue / mouth ulcers.
  • Tinnitus.
  • Depression.
  • Diarrhoea.
  • Loss of appetite / weight loss.
  • Almost any neurological problem from anxiety, panic to depression because low B12 affects the red blood cells and the nervous system.
  • …and More.

Low B12 might be detected by Total Serum B12, or possibly Active B12 (if you can get the test). However, both tests have severe drawbacks.

Total Serum B12 tests what the name implies, i.e. all circulating B12. This includes a large portion of B12, which is bound to protein and unavailable to the cells. There is a new test called the Holotranscobalamin test (the Active B12 test), that still measures B12 in the blood, and still does not show whether the B12 is truly adequate within the cells.

In the UK the reference range for Total Serum B12 is typically about 180 – 1000 pg/ml. With results below 180 pg/ml considered low, 180-350 pg/ml is considered borderline, and more than 350 pg/ml considered normal.

However, there is huge controversy over this. In other countries, the low end of the range is higher. In Japan, for instance, a patient would be put on routine B12 injections if their levels were below 500 pg/ml. Many B12 medical researchers and doctors who focus on the B12 issue consider that 550 pg/ml should be the low-end cut-off point.

It is also possible for some patients to have faults in their cell receptors and have high B12 results, but still be clinically B12 deficient.  There are pressure groups & charities working at the present to get the low-threshold of the B12 reference range, raised to at least 300 pg/ml and hopefully higher.

Active B12 has its own issues and researchers and doctors are still not entirely sure whether it is going to give a more reliable diagnosis than the Total Serum B12. This test still measures a blood level of B12 also – it does not reflect B12 that is actually active within the cells (as the name might imply to some readers).

Methyl Malonic Acid (MMA) is one of the better tests for B12 (a urine MMA test or a serum MMA are good). MMA is elevated in 90-98% of cases of low B12. MMA is an expensive test though. Sometimes MMA is not available. Homocysteine can also be used and is often elevated with low B12 – but it is not as reliable as MMA. Homocysteine can be high with folate deficiency, or low with methionine deficiency (common in vegans).

Pernicious Anaemia (PA) is severe anaemia brought about by the inability to produce enough Intrinsic Factor needed to absorb the B12 in the gut. PA has additional tests that can be done. These are the Parietal Cell Antibody test and the Intrinsic Factor Blocking Antibody test. But there are issues with these tests too. People with PA caused by either destruction of the Parietal Cells (which produce intrinsic factor and stomach acid), or destruction of Intrinsic Factor, invariably need B12 intramuscular injections to maintain their B12 levels. The frequency of these needs to be determined based on symptoms. Unfortunately, some countries have poor guidelines for how often these ought to be (the UK is currently one of these).  Many low B12 patients require self-administered B12 injections multiple times per week, in order to maintain their health.

Two important research papers appeared in the New England Journal of Medicine in 2012.

One research paper clearly showed that the presence of Intrinsic Factor Antibodies causes false-positive levels of B12 in the blood. This causes clinicians to rule out B12 deficiency.

A second paper in the same journal showed that the current machines that are used to test for B12, yield false-positive results in up to 35% of patients – again causing misdiagnosis. It is also known that Intrinsic Factor Antibodies only show positive in 40-60% of cases, and often have false-negative results! 

On top of all of this, any test of blood-based B12 does not necessarily show how well the B12 is being effective within the cells. No such test is possible yet. The tests for Intrinsic Factor Antibodies and Parietal Cell Antibodies are known to be unreliable and misleading.

The British Society for Haematology have guidelines on Intrinsic Factor Ab testing: “Patients negative for intrinsic factor antibody with no other causes of deficiency may still have pernicious anaemia, and should be treated as anti-intrinsic factor antibody-negative pernicious anaemia. Lifelong therapy should be continued in the presence of an objective clinical response”.

Furthermore, it is now known from research that:

  1. Low B12 levels can be present in the absence of enlarged red cells in over 60% of cases, and
  2. Neuro-psychiatric abnormalities due to low B12 can be present in a significant number of patients with normal haemoglobin and normal red blood cell count.

If low B12 is present, and you have a balanced diet, it is likely that you require proper treatment. Proper treatment probably means B12 injections.

To complicate things further, low folic acid can also have an impact; if it is low, you also cannot produce enough healthy red blood cells. So, testing Serum Folate is also important.

All in all, the current diagnosis methods for low B12 are flawed. The campaigners and doctors who specialise in B12 are aware of this and are pushing for major changes.

So, almost all the tests may show that everything looks completely fine with respect to B12. However, the person might still have low B12 and be struggling with the myriad of symptoms that can come from it, e.g. depression, fatigue, headaches, shortness of breath, diarrhoea, pins and needles, other neurological issues including paranoia and even psychosis to name but a few.

Left untreated, low B12 can result in permanent nerve damage! Permanent!

What if you have been on B12 supplements and then test B12?

If someone has been on any form of a supplement containing B12, it can leave the serum levels of B12 elevated for a long time afterward – in some cases 6 months!

If someone has been taking a B12 supplement, or even a multi-vitamin, this will artificially make the blood levels of B12 remain high. This is the case even though cellular levels of B12 can be desperately low and causing nerve damage!

This latter point makes the testing of B12 in the blood relatively futile once any treatment is started and is, therefore, not likely to result in any clear diagnosis.

If someone has been supplementing with B12 tablets or patches or sublingual tablets, their blood level of B12 is likely to be high, yet they may have inadequate cellular levels of B12. In many cases, the B12 taken this way is bound to protein and just continues to circulate in the bloodstream, i.e. it doesn’t get cleaved from protein and very little of it reaches the cells where it is needed. Hence, for someone with symptoms of low B12, it would be better to do the testing before any supplemental B12 is ever used. I have highlighted this last point as thyroid patients often take a lot of supplements in an attempt to ensure that they ‘have enough of everything’. For most of the other things, they might want to test, taking supplements will not cause much of an issue if the supplement is stopped first for a week or two prior to the testing. However, for B12 it makes a massive difference.

I cannot stress the last point enough, so please read this paragraph. If you have not had a B12 test prior to taking any supplement containing B12, you will probably not have true serum B12 result (with all of its faults). If you are on some form of B12, your results are likely to be high. The B12 test result is useless! Taking more oral B12 supplements (even sub-lingual) is likely not to help in many cases!

Please be aware that if you have been on oral supplementation of B12, and your results now look good or high, the B12 could still be dangerously low in the cells. So, supplementation ought to be avoided for many months if you plan to test B12.  You have to be off ALL B12 supplements for 4-6 months to get a valid B12 test result.

Oral B12 supplements just end up circulating around the body in some individuals. This B12 may not ever arrive within the cells. In some patients, the B12 can just remain bound to protein and never be released for use within the cells. Some patients have been known to appear to have good B12 levels due to supplementation. However, because their cells were starved of B12, they suffered permanent neurological damage. 

See the following document by the Dutch Research group, an official government group, the only one specifically mandated to research B12 in the world:

Once on B12 injections, serum levels remain high, which is needed to repair neurological damage, and there is no toxicity, as stated by the World Health Organisation. The injections are very high dosage, and they bypass the stage where it attaches to one protein and is blocked there. It gets cleaved. When you take a tablet, the gut attaches a protein that needs being cleaved along the way, and it does not happen if the circuit is broken somewhere. Additionally, there’s a 1% passive absorption in all forms of B12, but nowhere enough to repair the damage.

What does this all imply?

It means it is a very complex situation, and it can be extremely difficult to get a clear diagnosis of B12 deficiency or Pernicious Anaemia. 

Some people have methylation issues which affect their ability to convert some forms of B12 to the active form (methyl B12). Hydroxy or cyanocobalamin products can be less efficient for these people, and they may do better with methyl-cobalamin. This issue might possibly be detected by some of the genetic testing that can be done through companies like or However, interpretation of the results can be difficult. 

I worry that a lot of thyroid patients who are not responding to thyroid treatment may well have undiagnosed B12 issues.

Even if someone is diagnosed with low B12, they often fail to get the treatment that they need to keep the effects of low B12 at bay, i.e. the required frequency of intramuscular B12 injections. Many of them find that within a few weeks of a B12 injection, their symptoms are starting to return.

For these people, injections far more frequently are required. This is hard to get in some countries unless the patient has a good haematologist or doctor.

Some of the most affected PA patients need much more frequent injections e.g. every other day or twice per week. In these cases, being able to self-inject is a good option. B12 is very easy, and painless, to administer this way. Sometimes even regular intravenous B12 is required.

In most cases of seriously low B12, loading doses of frequent B12 are needed for a couple of weeks in order to get the levels up quickly. After this, the frequency of the B12 injections could be reduced to the level for the individual that keeps symptoms at bay.

All in all, the entire situation is a bit of a shambles.

The Pernicious Anaemia Society charity in the UK, chaired by Martyn Hooper, is trying to work with the medical profession and other groups to create awareness and bring about change. There is still a long way to go though.

If someone has symptoms that fit extremely well with B12 deficiency, or PA, and there is any doubt about the blood tests at all, it is worth seeking a referral to a good Haematologist. They ought to know that the clinical presentation is the most important thing

Sometimes a therapeutic trial of B12 injections is the only valid diagnostic test. Doing a proper trial and assessment of the person’s response to regular B12 injections might be the only way to reach a correct diagnosis.

In addition to all the above, there are numerous co-factors that may be needed to enable B12 to function correctly within the cells.

If Methyl-Cobalamin (methyl B12) is the chosen form of B12 then a supplement called Adenosyl-Cobalamin should be taken each day.

B12 and folate work together. One cannot work without the other. Look into Iron, Vitamin D and Magnesium levels as these can be deficient also, (this is common when the person has Parietal Cell Antibodies but these nutrients can be low even when this is not the case).

Beyond the above, it is essential to have functional B2 for B12 to cycle correctly. So, the for ideal B12 usage the person requires the following supplements: 150 mcg/day Iodide, 55 mcg/day Sodium Selenite (in some Selenium supplements), 100 mcg/day Soidum Molybdate (in some Molybdenum supplements), and at least 5 mg/day B2 (via B2 or a B complex).

Further Reading.

I recommend reading these excellent books by Martyn Hooper: What you Need to Know About Pernicious Anaemia and Vitamin B12 Deficiency, and Pernicious Anaemia: The Forgotten Disease. Both books cover both B12 deficiency and Pernicious Anaemia (the autoimmune version of low B12). 

A less easy, but also excellent read is ‘Could it be B12?’ by Pacholok and Stuart.

See also:


and this great video:

For more information, please see the postscript to this blog.

Best wishes,



I also attach a link to the 2014 guidelines on B12 and folate treatment from the British Society of Haematologists, and the summary of that from the Pernicious Anaemia Society (PAS), which is a little more digestible.

Summary for the diagnosis and treatment of cobalamin and folate disorders (from the British Society of Haematologists – for medical professionals) See:

Here is the summary of this report from Martyn Hooper of the Pernicious Anaemia Society:

In June  2014 the British Committee for Standards in Haematology issued new; revised Guidelines on Vitamin B12 and Folate. The new guidelines acknowledge the failings of the current assay used to determine B12 status in patients. Below are the main recommendations of the committee:

1. The clinical picture is the most important factor in assessing the significance of test results assessing cobalamin status because there is no ‘gold standard’ test to define deficiency.

2. Definitive cut-off points to define clinical and subclinical deficiency states are not possible, given the variety of methodologies used and technical issues.

3. In the presence of discordance between the test result and strong clinical features of deficiency, treatment should not be delayed to avoid neurological impairment.

4. The absence of a raised MCV cannot be used to exclude the need for cobalamin testing because neurological impairment occurs with a normal MCV in 25% of cases.

5. Some assays may give false normal results in sera with high titre anti-intrinsic factor antibodies.

6. It is not entirely clear what should be regarded as a clinically normal serum cobalamin level.

7. It is even less clear what levels of serum cobalamin represent ‘subclinical’ deficiency.

8. Neurological symptoms due to cobalamin deficiency may occur in the presence of a normal MCV.

9. IFAB is positive in only 40-60% of cases, i.e. low sensitivity, and the finding of a negative IFAB assay does not therefore rule out pernicious anaemia (hereafter referred to as AbNegPA).

10. Standard initial therapy for patients without neurological involvement is 1000ug intramuscularly [‘i.m.’] three times a week for 2 weeks. The BNF advises that patients presenting with neurological symptoms should receive 1000ug i.m. on alternate days until there is no further improvement.

11. Care must be taken if low dose supplements are prescribed, as such an approach risks the suboptimal treatment of latent and emerging pernicious anaemia with possible inadequate treatment of neurological features.

12. There are arguments against the use of oral cobalamin in initiation of cobalamin therapy in severely deficient individuals who have poor absorption, especially due to pernicious anaemia.

13. Patients with pernicious anaemia need treatment for life regardless of serum cobalamin levels.

Paul Robinson

Paul Robinson is a British author and thyroid patient advocate. The focus of his books and work is on helping patients recover from hypothyroidism. Paul has accumulated a wealth of knowledge on thyroid and adrenal dysfunction and their treatment. His three books cover all of this.

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  1. Mags on 5th June 2020 at 12:09 am

    Very interesting.
    Especially the fact that those of us who have under active thyroid are often recommended oral B12 but ‘ they are often left circulating around the body ………and never released into the cells’.
    Most of us with UAT never feel that the taking of prescribed thyroid medication relieves the symptoms and try to supplement our diets with vitamins and minerals including B12 in an effort to try to manage better. Are they doing any good ?.

    • Paul Robinson on 5th June 2020 at 10:59 am

      The important thing is to test B12 whilst not on supplementation. I prefer to see people also do a full blood count to look for evidence of low B12 in the red blood cell count and mean cell volume and to check haemoglobin. If people can also test methyl malonic acid this is also a really valuable test.

      There is no doubt that B12 injections are the best way to treat low B12, although the UK guidelines and most countries’ guidelines on frequency of these are woefully inadequate.

      Thanks for the comment!

      • Louise on 21st November 2020 at 10:13 pm

        Yes I am recently diagnosed from a blood test and the injections are helping! (It did take the Drs a while to get to the bottom of it though…..even though I was telling the symptoms ! ). Since learned it often gets mis diagnosed as fibro or CFS

        • Paul Robinson on 22nd November 2020 at 10:15 am

          Good news!
          It can take 6-12 months for more of the symptoms to improve.
          Best wishes, Paul

  2. Maggi aldous on 5th June 2020 at 9:56 am

    Very informative, thank you. Explains more than my doctor could..

    • Paul Robinson on 5th June 2020 at 10:59 am

      Thanks so much!

  3. Michelle Cheatley on 10th June 2020 at 11:14 pm

    I found the book Could It Be B12 very helpful, also the Movie for starters

    • Paul Robinson on 11th June 2020 at 9:45 am

      Yes, it is a great book.
      Thank you for your comment.

  4. Louise on 21st November 2020 at 10:08 pm

    Read “could it be B12” amazing insight and all explained

    • Paul Robinson on 22nd November 2020 at 10:14 am

      Yes, I have many years ago. It is one of the B12 books on my bookshelf.
      Some of Martin Hooper’s books are excellent too.
      Best wishes, Paul

  5. Claire Boyle on 1st January 2021 at 8:13 pm

    I woke up three years ago with a numb left lip, left side of face, top of my head, left arm and fingers. After being hospitalized with a suspected stoke but a clear CT scan I was told by a team of neurologist that they suspect MS. Two years of MRI’s then I found a new GP who said my Ferritin level was 6. Following a 1 gram iron infusion still no great change. I watched your video about 6 months ago and started B12 1000mcg a day tablets and am feeling almost back to some kind of normal, including clear eyesight. Thank you so much

    • Paul Robinson on 2nd January 2021 at 3:32 pm

      Hi Claire, I’m sorry it took so long and that it must have been a scary journey for you.
      However, I am pleased that it is now more or less working. I hope you take food-based vitamin C with any iron supplementation as it helps absorption. Sometimes Heme Iron also helps – Google it. You’re also lucky that B12 tablets actually work as often they don’t and people need injections of B12 – often regular.
      Continued good luck with your health!

      • Claire Boyle on 26th January 2021 at 10:28 am

        Thanks so much and no just taking regular vitamin C so will change that.

        • Paul Robinson on 26th January 2021 at 11:22 am

          Reg vitamin C does help iron absorption in some people, but if your iron is not going up as expected then try the whole food vitamin C as this very often works.
          Best wishes, Paul

  6. Cathy Cross on 2nd January 2021 at 12:28 pm

    I’m on 100micrograms levothyroxine daily which has been reduced from 150, I have 3 monthly B12 injections, my doctors refuse to give these any sooner. By 8 weeks it’s like life is draining out of me, I have a numb feeling in my lower legs and tingling in my feet always. What can I do to help myself?

    • Paul Robinson on 2nd January 2021 at 3:35 pm

      B12 frequently needs to be given more often than once every 3 months. You could contact the main B12 charity and see if they have any advice. I know some people manage to get their B12 from other countries and self administer – it is very easy to do the B12 injections into the quad and their are plenty of videos on YouTube on this. Once a month B12 is common and some need it every other day!!
      Good luck Cathy.

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