Vitamin B12

Vitamin B12 is an essential component in our diet since it is a compound that intervenes in very important metabolic processes both at a neurological level, synthesis of red blood cells and of certain amino acids necessary for the synthesis of proteins.

Its deficit can generate neurological problems and certain anemias. This risk can be even greater in people who follow a vegan diet, since foods of vegetable origin, – exclusive diet of vegans -, do not contain Vitamin B12

Vitamina b12 o Cobalamina

What is Vitamin B12?

Vitamin B12, also known as Cobalamin (the name is due to the presence of a Cobalt atom in its molecular structure), is a water-soluble vitamin that is naturally present in some foods of animal origin. It has a complex chemical structure in which according to the radical that is attached to the Cobalt atom will give rise to:

Cyanocobalamin, if coupled with a cyanide radical CN

Hydroxocobalamin, if a hydroxyl radical OH

Methylcobalamin if the radical is a methyl CH3

The Cyanocobalamin form is synthetic, obtained from Hydroxocobalamin and is the most used in pharmaceutical products due to its greater stability and resistance to oxidation.

Vitamin B12 is an essential vitamin, that is, our body does not have the capacity to synthesize it and it must be ingested with the diet, through food or through supplements containing this vitamin.

Actually, it should be mentioned that there is a certain capacity of synthesis of Vitamin B12 in our organism, thanks to the bacteria that form our intestinal microbiota, but this production of Vitamin B12 takes place in the large intestine, where there is no longer absorption and where all the Vitamin B12 produced is excreted directly together with the feces.

Vitamin B12 is only present in food of animal origin

Benefits of Vitamin B12 and what it is good for

Vitamin B12 is necessary for the synthesis of DNA (deoxyribonucleic acid) and in particular it is necessary in the synthesis and formation of our red blood cells as well as in the synthesis of myelin, a lipoprotein material that forms a sheath covering the nerve fibers.

Vitamin B12 also acts as a cofactor in methionine synthase, an enzyme that catalyzes the conversion of homocysteine into methionine, the latter being an amino acid involved in the synthesis of other amino acids such as cysteine or taurine. Therefore, a deficit of Vitamin B12 will generate an increase in homocysteine in the blood as it cannot be metabolized to methionine. This excess of homocysteine in the blood can cause cardiovascular problems and is in fact one of the markers used in patients with pathologies of this type.

Vitamin B12 is also involved in the synthesis of Succinyl CoA from L-methylmalonyl-CoA, which is required in the synthesis of hemoglobin.

Foods containing Vitamin B12

As we mentioned at the beginning, Vitamin B12 is only found in foods of animal origin and is not present in those of vegetable origin.

Among the main foods with Vitamin B12, we have

  • Clams. Provides a large amount of Vitamin B12, about 3,500 % of the daily amount patched
  • Liver. It is also an important source with a contribution of approximately 3,000 % of the recommended daily amount
  • Sardines. They provide around 500 % of the recommended daily amount.
  • In smaller proportion: trout, tuna, dairy products and eggs
Alimentos ricos en Vitamina B12
Natural sources of Vitamin B12 (Cobalamin).

The Intrinsic Factor

Intrinsic factor is a glycoprotein synthesized in the parietal cells of the stomach and is necessary for the absorption of vitamin B12.

This intrinsic factor binds to dietary vitamin B12, forming an FI-B12complex, which, once in the ileum, in the small intestine, binds to receptors located at this level. The complex is then absorbed and passes into the bloodstream where it binds to a protein, a transcobalamin, which acts as a transport medium for vitamin B12 and will carry it to the liver and other organs.

Intrinsic factor synthesis usually begins to decline after age 60, which means less vitamin B12is absorbed, even if we eat enough of it in the diet.

Certain situations such as atrophic gastritis, which cause damage to the gastric cells of the stomach and, as a consequence, a reduction in the synthesis of intrinsic factor, also cause a decrease in the absorption capacity of Vitamin B12.

Prior to the binding of vitamin B12to intrinsic factor, there must be a detachment of vitamin B12from food proteins. This disunion is exerted by pepsin and gastric juices at an acidic pH, which is very low, so situations of achlorhydria and low acidity can also cause less absorption of vitamin B12.

Daily requirement of Vitamin B12

The daily requirement of vitamin B12varies between American and European agencies. While in the United States the current recommended daily intake is 2.4 µg/day (1), in Europe the EFSA recommends at least 4 µg/day of vitamin B12 for the adult population (2)

One of the main causes of Vitamin B12 deficiency is pernicious anemia

Vitamina B12 deficiency

It is considered a deficit of Vitamin B12 when its concentration in blood is below 211 pg/ml, being the reference values in blood between 211 and 911 pg/ml.

Vitamin B12 is stored in the liver and this reserve can last between 2 and 5 years so that a diet with low Vitamin B12 does not become apparent until several months later, when liver reserves begin to decline.

Causes of Vitamin B12 Deficiency

Among the causes that cause a deficit of vitamin B12absorption, are

Pernicious Anemia

Pernicious anemia is an autoimmune disease that produces a destruction of the parietal cells in charge of producing and secreting Intrinsic Factor which, as we saw before, is necessary for the absorption of Vitamin B12. As a consequence of this reduction of Intrinsic Factor synthesis, a lower absorption of Vitamin B12 is produced.

Vegan Diet

A vegan diet is based solely on foods of plant origin and does not contain vitamin B12. People who follow a vegan diet should supplement to avoid problems resulting from low vitamin B12.

Intestinal absorption problems

Certain pathologies, such as Crohn’s Disease or Celiac Disease that affect the correct absorption of nutrients can also generate a deficit in the absorption of Vitamin B12.

Interaction with some drugs

Treatment with some medications that can increase the gastric pH, such as antacids or omeprazole, which inhibits the proton pump, anti-H2 antihistamines (cimetidine, ranitidine) can generate problems of vitamin B12 absorption by modifying the pH that is needed for the disunion of vitamin B12from proteins in the diet.


In senile population there is an increased risk of malabsorption of Vitamin B12due to lower stomach acidity, frequent treatments with antacids, lower capacity of Intrinsic Factor synthesis due to age.

Symptoms of a Vitamin B12 deficit

Megaloblastic Anemia

In a situation of low vitamin B12, a type of anemia called megaloblastic anemia occurs in which the formation of red blood cells is slower, resulting in abnormally large red blood cells.

These red blood cells have a lower capacity of oxygenation of tissues leading to other symptoms such as tiredness, pallor or headache.

Neural problems

Numbness and tingling in extremities, with possible balance problems, memory problems due to the impact this vitamin has on the nervous system.

Cardiovascular problems

Vitamin B12is involved in the synthesis of methionine from homocysteine. If we are in a situation of low vitamin B12, there will be an increase in homocysteine which will result in an increased risk of cardiovascular problems.

Treatment of Vitamin B12 deficiency

In advanced states of Vitamin B12 deficiency with pernicious anemia, injectables are used with an initial dose of 1,000 µ/day which is then gradually reduced with lower doses until the hepatic storage of Vitamin B12is recovered

In the case of preventive treatments of possible states of deficiency, the usual pharmaceutical form is tablets of Vitamin B12 accompanied by other vitamins and in daily doses of about 2 – 4 µ/day.

One of the usual complexes is formed by vitamins B1, B6 and B12. The joint action of these three vitamins is related to pain receptors. This complex of Vitamins B1, B6 and B12 is sometimes administered together with anti-inflammatory drugs (diclofenac) as they can help improve pain reduction.