Vitamin B12 is needed for the making of blood cells, for the healthy working of the nervous system and for DNA synthesis.
Finding a low B12 level on a blood test does not come only from an inadequate diet. Sometimes it is one of the first signs of a problem with absorption in the stomach or small bowel.
With a low B12, what matters is not only replacing the vitamin but — particularly where the deficiency is marked or keeps coming back — looking into why it fell.
What does vitamin B12 do?
Vitamin B12 plays an important part in:
- The making of red blood cells
- The normal working of the nervous system
- DNA synthesis
- Maintaining the normal function of cells
If the deficiency goes on for a long time, both anaemia and neurological problems can appear.
Why does vitamin B12 fall?
The causes of B12 deficiency can be looked at in several main groups.
1. Not taking in enough B12
Vitamin B12 is found mainly in foods of animal origin. A diet that does not contain enough B12 over a long period — particularly a vegan diet without appropriate supplementation — can cause B12 deficiency.
But diet is not the only cause of B12 deficiency.
2. Diseases of the stomach
The stomach plays an important part in allowing B12 to be absorbed from the bowel. Intrinsic factor, produced by the parietal cells of the stomach, is needed for B12 to be absorbed from the small bowel. So the following can lead to B12 deficiency:
- Autoimmune gastritis
- Atrophic gastritis
- Pernicious anaemia
- Surgical removal of part or all of the stomach
- Some bariatric operations
What is pernicious anaemia?
Pernicious anaemia is one of the important causes of impaired B12 absorption. The immune system can develop antibodies against intrinsic factor or against the parietal cells of the stomach. The result is that less B12 is absorbed.
Where this is suspected, your doctor may use anti-intrinsic factor antibody, anti-parietal cell antibody and other tests as needed.
Pernicious anaemia should not be seen simply as a “vitamin deficiency”; the underlying autoimmune gastritis needs assessing as well.
3. Malabsorption in the small bowel
B12 is absorbed mainly in the terminal ileum, the last part of the small bowel. So the following can cause B12 deficiency:
- Crohn’s disease affecting the terminal ileum
- Surgical removal of the terminal ileum
- Some malabsorption conditions
- Some other conditions of the small bowel
4. Can medicines lower B12?
Yes. Long-term use of some medicines can affect the B12 level. In particular:
- Metformin
- Some acid-suppressing stomach medicines taken over a long period
can be associated with B12 deficiency.
Do not stop your medicine on your own
Do not stop these medicines yourself because your B12 came back low.
Does B12 deficiency cause anaemia?
Yes.
As B12 deficiency progresses, the normal production of red blood cells can be disturbed and megaloblastic anaemia can develop. The blood count may show a low haemoglobin and a raised MCV.
But there is a very important point here: B12 deficiency can be present even when haemoglobin and MCV are normal. Particularly early on, or where there are other deficiencies alongside, the classic blood picture may not be seen.
Does B12 deficiency affect the nervous system?
Yes. In long-standing or severe B12 deficiency, neurological symptoms can appear:
- Numbness in the hands and feet
- Pins and needles
- Loss of sensation
- Problems with balance
- Difficulty walking
- Muscle weakness
- Problems with concentration and thinking
Neurological findings can appear before anaemia develops. So it is not right to assess B12 deficiency by looking at the haemoglobin value alone.
Can it cause symptoms in the mouth and tongue?
Yes. Some people have burning of the tongue, flattening of the tongue’s surface, a red and tender tongue, and discomfort in the mouth.
What are the symptoms of B12 deficiency?
B12 deficiency can cause weakness, tiredness, tiring easily, pallor, dizziness, palpitations, breathlessness, numbness and pins and needles, problems with balance and burning of the tongue.
But some people have no obvious symptoms even with a quite low B12.
What should B12 be?
Reference ranges can vary with the laboratory and the method used. So it is not right to give a single universal cut-off.
In borderline results particularly, the serum B12 level alone may not be enough. Where needed, your doctor may use additional tests such as methylmalonic acid (MMA) and homocysteine. In B12 deficiency the MMA level in particular can rise.
Is a gastroscopy needed if B12 is low?
Not every low B12 needs a gastroscopy. But more detailed assessment of the stomach and gastrointestinal tract may be needed where there is:
- B12 deficiency with no explanation
- Recurring or persistent deficiency
- Suspected autoimmune or atrophic gastritis
- Pernicious anaemia
- Accompanying gastrointestinal symptoms
Whether a gastroscopy is needed is decided from the person’s clinical features.
Is a B12 injection better than tablets?
There is no single answer to this question.
Treatment is planned according to how severe the deficiency is, what is causing it, whether there are neurological symptoms and the state of absorption.
In some patients high-dose oral B12 may be enough, while in other situations B12 by injection may be preferred. The form of treatment should be decided for each person.
Can I stop treatment once B12 is back to normal?
That depends on the cause of the deficiency.
A temporary deficiency related to diet is not the same as B12 deficiency due to pernicious anaemia or a permanent absorption problem. Some people with permanent malabsorption may need long-term, even lifelong, B12 replacement.
So the B12 value coming back to normal does not on its own show that the cause of the deficiency has gone.
Why does its relationship with folic acid matter?
B12 and folate deficiency can cause similar findings on the blood count.
Giving folic acid alone to someone with B12 deficiency may partly correct the anaemia while failing to prevent neurological damage from the B12 deficiency progressing.
This is why B12 and folate should be considered together, particularly in assessing macrocytic anaemia.
Which tests may be done if B12 is low?
Depending on the patient’s situation, investigations such as the following may be done:
- Full blood count
- MCV
- Folate
- Ferritin and iron studies
- Methylmalonic acid
- Homocysteine
- Anti-intrinsic factor antibody
- Anti-parietal cell antibody
Not every patient needs all of these tests.
When should assessment not be delayed?
Assessment should not be delayed if a low B12 is accompanied by
New difficulty with walking or balance · marked muscle weakness · progressive numbness or loss of sensation · a change in consciousness or marked change in thinking · breathlessness, palpitations or fainting from severe anaemia.
What should you do if B12 is low?
- Do not judge the result on its own. It should be weighed together with the blood count, MCV, folate and, where needed, other tests.
- Think about the cause of the deficiency. Particularly where it is marked or recurring, giving B12 alone may not be enough.
- Do not overlook conditions of the stomach and bowel. Atrophic gastritis, pernicious anaemia and diseases of the terminal ileum are among the important causes.
- Tell your doctor about the medicines you take. Metformin and long-term acid-suppressing treatment matter in particular.
- Do not delay if there are neurological symptoms. B12 deficiency can affect the nervous system.
Remember
- A low B12 Does not mean simply an inadequate diet.
- The stomach Plays an important part in B12 absorption through intrinsic factor.
- The terminal ileum Is the main part of the bowel where B12 is absorbed.
- A normal haemoglobin Does not rule out B12 deficiency.
- Neurological symptoms Can develop without anaemia.
- Treatment Can be given by mouth or by injection, depending on the cause and severity.
- A recurring low B12 Calls for its cause to be looked into.
This is not enough to make a diagnosis
A low vitamin B12 has to be weighed together with the serum B12 level, the blood count, the MCV, your diet, the medicines you take, conditions of the stomach and bowel and, where needed, further laboratory tests.
Particularly with recurring or unexplained B12 deficiency, what matters is determining the cause rather than simply taking the vitamin.
Sources
- Prof. Ali Tüzün İnce, MD