Vitamins B12 - Sources, Foods, Benefits, Lies
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Vitamin B12, also called cobalamin, is an essential vitamin in the formation of red blood cells and in the functioning of the nervous system. 

What are the risks of vitamin B12 deficiency and where to find this vitamin in the diet? Here’s everything you need to know about cobalamin.

Description of Vitamin B12

A B-complex vitamin, vitamin B12, or cobalamin, comes in the form of a red crystalline compound earning it the nickname “red vitamin”. The name cobalamin refers to its cobalt content, unique among vitamins.

Cobalamin is essential for growth, cell division, proper functioning of all cells in the body, and balance of the nervous system.

Vitamin B12 intervenes more precisely in the synthesis:

  • DNA and RNA;
  • proteins;
  • myelin (a substance that forms a sheath around certain nerve fibers);
  • in the formation of red blood cells;
  • as well as in the metabolism of carbohydrates and lipids.

The absorption of vitamin B12 requires the presence of hydrochloric acid as well as association with a substance secreted by the stomach lining (intrinsic factor). It can then be stored by the body in the liver, pancreas, heart, and brain.

Because these B12 stores are large, it can take years for symptoms caused by a deficiency to appear. Unlike other B vitamins, which are excreted through urine, B12 is eliminated through bile.

Cyanocobalamin is a synthetic form of B12 used in most supplements.

Indications of vitamin B12


Vitamin B12 helps to:

  • treat vitamin B12 deficiency;
  • prevent cardiovascular diseases (in combination with vitamins B6 and B9);
  • treating disorders in Alzheimer’s disease;
  • prevent side effects of angioplasty.

Vitamin B12 has other recognized or potential therapeutic uses that require medical monitoring, for example, the treatment of megaloblastic anemia, pernicious anemia, or even diabetic neuropathy.

Dosage of vitamin B12


Vegetarians who do not eat foods of animal origin or foods fortified with vitamin B12 (Red Star yeast or fortified soy beverages, for example) are recommended to take B12 supplements.

Vitamin B12 supplements, like other B vitamins, are best absorbed when taken with a meal.

Recommended dietary intake of vitamin B12

(µg* per day)
from 0 to 6 months0,4 µg**
from 7 to 12 months0,5 µg**
from 1 to 3 years0,9 µg
from 4 to 8 years old1,2 µg
from 9 to 13 years old1,8 µg
14 years and over2,4 µg
Pregnant women2,6 µg
Nursing women2,8 µg

*µg = microgram = 1 millionth of a gram
**In the absence of sufficient scientific data, the authorities have set, not a recommended nutritional intake (ANR), but an adequate intake (AS). Adequate B12 intake is based on average intakes observed in healthy North American babies.

Food sources of B12

In food, vitamin B12 is mainly found in animal products, including organ meats and shellfish.

Some products of plant origin contain it, such as miso or spirulina, but it is not certain that their form can be absorbed by the body.

Breakfast cereals, Red Star nutritional yeast, and some soy beverages are fortified with vitamin B12.

FoodPortionsVitamine B12 (µg*)
Canned clams100 g (3 ½ oz) (13 medium)99 µg
Cooked beef liver100 g (3 ½ oz)71 µg to 83 µg
Kidneys and livers of lamb, turkey and veal, braised
100 g (3 ½ oz)
37 µg to 77 µg
Tomato and clam cocktail125ml (1/2 cup)39 µg
Octopus, boiled100 g (3 ½ oz)36 µg
Pacific oysters, raw or steamed100 g (3 ½ oz) (2 to 4 medium)16 µg to 28 µg
Veal brain, sautéed or braised100 g (3 ½ oz)10 µg to 21 µg
Crab, steamed100 g (3 ½ oz)7 µg to 12 µg
Tuna, grilled100 g (3 ½ oz)11 µg
Chicken giblets, stewed100 g (3 ½ oz)9 µg
Sardines, canned with bones100 g (3 ½ oz) (8 medium)9 µg
Salmon, canned, baked, grilled, or smoked100 g (3 ½ oz)4 µg to 6 µg
Rainbow trout, baked or grilled100 g (3 ½ oz)5 µg
Herring, marinated100 g (3 ½ oz)5 µg
Beef and veal, all parts, cooked100 g (3 ½ oz)2 µg to 4 µg
Tuna, canned100 g (3 ½ oz)2 µg to 4 µg
Egg, yolk only, raw30 g to 60 g (2 to 4 yolks)3 µg
Swordfish, baked100 g (3 ½ oz)2 µg
Shrimp, steamed100 g (3 ½ oz)2 µg
Lamb, all parts, braised100 g (3 ½ oz)2 µg

*µg = microgram = 1 millionth of a gram

Vitamin B12 deficiency

Vitamin B12 reserves in the body are important.

Symptoms attributable to a deficiency can therefore take months or even years to appear and are difficult to diagnose.

Vitamin B12 deficiency causes:

  • tiredness;
  • weakness;
  • shortness of breath;
  • nausea ;
  • constipation;
  • flatulence;
  • loss of appetite and weight loss.

Vitamin B12 deficiency can also cause neurological symptoms:

  • tingling and numbness in the limbs;
  • difficulty walking;
  • mood disorders ;
  • memory loss and dementia.

B12 deficiency is often associated with an absorption problem.

The B12 present in food is bound to proteins from which it separates under the action of stomach acid and enzymes. Once detached from the protein, it must bind to the intrinsic factor, a substance secreted by the lining of the stomach, to pass into the blood.

Vitamin B12 absorption is reduced if one of the two steps is slowed down or prevented. People with pernicious anemia (or Biermer’s anemia) do not secrete the intrinsic factor essential for the absorption of vitamin B12.

It is estimated that 10% to 30% of older people have difficulty absorbing vitamin B12 due to low stomach acid. US authorities recommend that people over 50 get their vitamin B12 from supplements or foods fortified with B12, because in this form it is easily absorbed, even with low stomach acid.

Vegans, who do not consume any animal products, are at risk of vitamin B12 deficiency. There is controversy about this because the human body has significant reserves of B12 and intestinal bacteria are able to synthesize small amounts.

However, most sources claim that a diet completely devoid of B12 will eventually, after a few years, deplete these stores.

Pregnant or nursing vegan women should make sure they get enough vitamin B12 in their diet (Red Star yeast and fortified soy beverages, for example) so that their child doesn’t deplete their low stores.

Precautions to take with vitamin B12


Since the symptoms of a serious B12 deficiency can be masked by taking folic acid in high doses (more than 1,000 µg per day), this should be done under medical supervision.

This deficiency can lead to irreversible neurological damage.


  • None at usual doses;
  • people with cardiovascular disease, having suffered a myocardial infarction, or at high risk of cardiovascular disease. Very high doses of vitamins B6, B9, and B12 taken for long periods can increase the risk of relapse of cardiovascular disorders and death.

Side effects

Vitamin B12, even in high doses, appears to be safe. However, very high doses can make acne worse.

Interactions with vitamin B12

With plants or supplements

Taking potassium supplements can reduce the absorption of B12.

With medication

All drugs that reduce gastric acidity may reduce the absorption of vitamin B12 from food. However, they do not interfere with the absorption of supplements:

  • H2 receptor antagonists (ranitidine – Zantac, for example, but only long-term);
  • proton pump inhibitor (omeprazole – Losec), for example.

Metformin and phenformin, hypoglycemic drugs, can reduce the absorption of vitamin B12. However, this effect can be corrected by the simultaneous intake of milk or calcium carbonate supplements.

Taking colchicine (gout medicine), cholestyramine (cholesterol medicine), chloramphenicol, and neomycin (antibiotics) can reduce the absorption of vitamin B12 from food.

Vitamin B12 Research

Vitamin B12 deficiency

Vitamin B12 deficiency is a cause of megaloblastic anemia, an event in which red blood cells are abnormally large.

There are several causes associated with this form of anemia, including folic acid deficiency or other metabolic disorders. This form of anemia is effectively treated with vitamin B12 intake.

Vitamin B12 deficiency can lead to various neurological and behavioral disorders such as:

  • ataxia;
  • muscle weakness;
  • incontinence;
  • low blood pressure;
  • visual disturbances;
  • psychotic and mood disorders.

People at risk of developing vitamin B12 deficiency include vegetarians, the elderly, and breastfed babies.

Several studies have demonstrated the effectiveness of vitamin B12 administration (up to 2,000 mg) orally or intramuscularly in the prevention or treatment of vitamin B12 deficiency.

Cardiovascular illnesses

High blood levels of homocysteine ​​increase the risk of cardiovascular disease, blood clot formation, and atherosclerosis.

The authors of a meta-analysis concluded that daily supplementation with B vitamins can reduce high levels of homocysteine ​​in the blood. 

While another study reports a decrease in lipid deposits on the arteries in individuals treated with a combination of B vitamins.

The doses used in these studies ranged from 0.02 to 1 mg of vitamin B12, in combination with 1.5 mg of folic acid and 5-50 mg of vitamin B6.

However, it remains to be determined that this drop in homocysteine ​​levels decreases mortality linked to cardiovascular diseases. Indeed, it is not clear that the decline in these levels is causally related to the onset of these diseases.

Alzheimer’s disease

Several studies report vitamin B12 deficiency in patients with Alzheimer’s disease. However, the effectiveness of vitamin B12 intake on cognitive and behavioral disorders remains to be demonstrated.


The results concerning the effectiveness of a combination of folic acid and vitamins B6 and B12 are contradictory.

One study reported that this B vitamin combination reduces the risk of an adverse cardiac event following angioplasty.

Another team of researchers has however shown that this combination increases the risk of restenosis (new obstruction of the coronary arteries).

be cancer you

Researchers from Johns Hopkins University (USA) have reported that women with breast cancer have lower blood levels of vitamin B12 than those who have not developed cancer.

However, another study found no association between vitamin B12 levels and breast cancer risk.

On the other hand, no reducing effect of a combination of folic acid and vitamins B6 and B12 was observed on the risk of breast cancer. This result remains to be confirmed.

History of vitamin B12

In 1925, an American researcher demonstrated that eating liver cured anemia in dogs. However, it was not until 1948 that English and American scientists, working separately, isolated a red pigment from the liver and named it vitamin B12.

Later that year, American researchers demonstrated that injections of this substance cured pernicious anemia, so-called by doctors who did not know how to treat this strange form of anemia, against which the administration of iron supplements was ineffective.

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