Vitamin B12 deficiency anemia

This form of anemia occurs as a result of a lack of vitamin B12 (cobalamin). Vitamin B12 is essential for the formation of red blood cells, in particular. This anemia forms very slowly, after months or years of vitamin deficiency. The elderly are the most affected: around 12% of them are said to be suffering from a deficiency in this vitamin, without necessarily having anemia 1 .

Vitamin B12 is obtained by consuming foods of animal origin, such as meat, eggs, fish and shellfish. For most people, food gives the body much more B12 than it needs. The excess is stored in the liver. It is possible to suffer from anemia from a lack of B12 in the diet, but it is rare. Most often, anemia results from a problem with the absorption of the vitamin.

The pernicious anemia affect 2% to 4% of the general population 2 . It is most likely underdiagnosed because the symptoms are not always obvious to detect.

 Causes of B12 deficiency anemia

An inability to properly absorb vitamin B12 from food: this is the most common cause. Here are the main elements that can lead to poor absorption.

  • A lack of intrinsic factor . Intrinsic factor is a molecule secreted in the stomach which allows the absorption of vitamin B12 in the small intestine by binding to it (see diagram). For the binding between intrinsic factor and B12 to occur, there must be a normal degree of acidity in the stomach. When the anemia is caused by a lack of intrinsic factor, it is called pernicious anemia or Biermer’s anemia. Genetic factors would intervene. 
  • Low acidity in the stomach.  Between 60% and 70% of vitamin B12 deficiencies in the  elderly  are thought to be attributable to a lack of gastric acidity 1 . With age, stomach cells secrete less stomach acid and also less intrinsic factor. Regular and prolonged use of   antacid drugs 3 , such as histamine blockers (eg ranitidine) but particularly from the class of proton pump inhibitors (eg omeprazole) also increases the risk 1 .
  • Taking metformin. People who take metformin, mostly to treat diabetes, are at greater risk for vitamin B12 deficiency 4 .
  • An autoimmune disease ( Graves disease , thyroiditis , vitiligo, etc.): in these cases, autoantibodies will bind the intrinsic factor, making it unavailable to bind vitamin B12. 
  • Chronic bowel disease , which prevents vitamin B12 from passing through the intestinal wall (for example, Crohn’s disease, ulcerative colitis, or celiac disease). Taking vitamin supplements is usually suggested by the doctor to prevent deficiencies. In the case of celiac disease, absorption of vitamin B12 returns to normal once the  gluten-free diet  is adopted. Any other disease leading to malabsorption, such as chronic pancreatitis or very rarely parasite infestation can cause vitamin B12 deficiency.
  • Certain stomach or small intestine surgeries . Patients receive preventive vitamin B12 supplementation.
    Anemia can also be caused by a  lack of vitamin B12  in  the diet . But this situation is rather rare, since it only takes small amounts of B12 to meet the body’s needs. In addition, this one has the capacity to make important reserves, which can be sufficient to the needs during 3 or 4 years. Strict vegetarian (also called veganism ) followers  , who do not consume animal protein, may suffer from anemia in the long term if they do not otherwise meet their B12 needs (see Prevention). Research has shown that 92% of vegans are deficient in vitamin B12 if they do not take a supplement, compared to 11% of omnivores 5 .
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The deficiency anemia B12 moved very slowly, insidiously. However, this anemia can be treated quickly and easily. From the first days of treatment, the symptoms subside. Within a few weeks, the deficiency can usually be corrected.

However, it is important to treat this type of anemia, because over the years,  neurological symptoms  may appear (numbness and tingling in the extremities, gait disturbance, mood swings, depression, psychosis, symptoms of dementia, etc.). These symptoms take longer to disappear (sometimes 6 months or more). Sometimes there are still sequelae.

People with pernicious anemia are also slightly more at risk of stomach tumors than the rest of the population.


The anemia caused by B12 deficiency is detected by various blood tests. The following abnormalities are signs:

  • a decrease in the number of red blood cells, white blood cells and platelets;
  • a decrease in the hematocrit, that is to say the volume occupied by red blood cells relative to that of blood;
  • a lowered hemoglobin level ;
  • an increased size of red blood cells (mean globular volume or MCV): it may however remain stable if iron deficiency anemia (iron deficiency) is also present;
  • a change in the appearance of red blood cells and white blood cells, which can be seen by examining a blood smear.
  • There can be vitamin B12 deficiency without anemia.
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The doctor also checks the levels of vitamin B12, folic acid and iron in the blood. We must also find out the cause of the anemia. If vitamin B12 deficiency is detected, testing for intrinsic factor autoantibodies is often undertaken.

Note . The deficiency of folic acid (vitamin B9) produces the same type of effect on the red blood cells: they enlarge and become deformed. However, B9 deficiency anemia does not cause neurological symptoms.

Symptoms, people and risk factors for vitamin B12 deficiency anemia


There are not always obvious symptoms. These appear gradually.

  • Typical symptoms of anemia are: fatigue, a pale and sometimes yellowish complexion, dizziness, increased heart rate and increased shortness of breath on exertion.
  • A weak appetite.
  • Sometimes nausea and disturbed digestion (diarrhea or constipation).
  • The tongue is red and dry.
  • Neurological symptoms, in case of greater deficiency: numbness and tingling in the extremities, poor coordination, mood disorders, memory loss, dementia.

People at risk

  • Men and women 65 years of  age and over .
  • People from Northern Europe (Caucasians) and African Americans.
  • Vegetarians and vegans
  • Patients with autoimmune diseases (Graves, vitiligo)
  • People who use metformin and certain antacids
  • People with certain types of stomach or bowel surgeries
  • People with malabsorption from any cause (crohn, celiac, chronic pancreatitis, etc.)
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Prevention of B12 deficiency anemia

Screening measures
Testing for vitamin B12 deficiency in the elderly is an increasingly common practice.Most people with an autoimmune disease need more than one blood test per year to monitor vitamin B12 levels, among other things.Check with your doctor.
Basic preventive measures
Have an adequate dietary intake of vitamin B12. The vegans can find vitamin B12 in yeast fortified with B12 (Red Star Lyfe), the fortified soy beverages, rice fortified beverages and faux meats (often made from soy protein).The best sources of vitamin B12:
– organ meats (beef, pork, veal, poultry, kidneys, brains, etc.);
– meat, poultry, fish and seafood;
– eggs and dairy products.Consult our Vitamin B12 sheet to see the list of foods that contain the most. See also the advice of nutritionist Hélène Baribeau for vegans: Vegetalism.

Medical treatments and complementary approaches to vitamin B12 deficiency anemia

Medical treatments

While patients with malabsorption were routinely treated with intramuscular injections of vitamin B12, it is now known that oral supplementation, at higher doses, is most of the time as effective 6 . If the treatment is adequate, the patient’s condition improves within a few days. This treatment is devoid of any side effects.

In severe cases,   blood transfusions may be necessary, if the anemia is very severe, until vitamin therapy can take effect.

Complementary approaches

There is no recommended complementary approach for vitamin B12 deficiency. One can consult the sheets for the support of the diseases which are associated.

Vitamin B12 Deficiency Anemia – Our Doctor’s Opinion

Vitamin B12 deficiency is not uncommon. It affects 5% to 10% of people over 65, and often goes unnoticed. If you suffer from anemia secondary to this deficiency, the treatment is simple and very effective: vitamin B12 by mouth or more rarely by injection.

If you have to use metformin or antacid drugs from the proton pump inhibitor class, such as omeprazole or pantoprazole, it is worth asking your doctor whether to test for vitamin B12 in your drug. blood during your periodic exam. 


Ask DrWeil, Polaris Health (Ed). Q&A Library – Not enough B12 ?, .
Mayo Foundation for Medical Education and Research (Ed). Diseases & Conditions – Anemia, .
Mayo Foundation for Medical Education and Research (Ed). Diseases & Conditions – Vitamin deficiency anemia, . .
National Institute of Health. Dietary Supplement Fact Sheet – Vitamin B12,  Office of Dietary Supplements. .
National Library of Medicine (Ed). Medline Plus Health Information, Health topics – Anemia,  Medline plus .
National Library of Medicine (Ed). PubMed,  NCBI . [Accessed May 16, 2011].