Vitamin B12: what it is and how to take it

Vitamin B12: what it is, how to take it and symptoms of deficiency or excess

The vitamin B12 it is to be counted among the water-soluble vitamins of group B. Also known as cobalamin or cyanocobalamin, it was discovered following research relating to pernicious anemia. In 1926, scholars discovered that there was something in the liver capable of curing this disease, but this compound was only isolated in 1948.

However, it was necessary to wait until 1956 before the structure of vitamin B12 was defined. But let’s get to know this element better by going to see what is it for, where it is, Which foods contain it and what symptoms cause its deficiency or excess.

Vitamin B12: what it is and what it is used for

Vitamin B12 is a red colored molecule, water-soluble and photosensitive. In its chemical composition the presence in the center of a stands out cobalt atom: hence the alternative name of cobalamin. There are several forms of this vitamin, the most common are:

  • methylcobalamin
  • hydroxocobalamin
  • deossiadenosilcobalamina

Not all forms of cobalamin are active: the methyl- and 5′-deoxyadenosylcobalamin forms are. Usually the natural form of the vitamin that is taken with the diet is thehydroxocobalamin, while the term cyanocobalamin refers to an artifact created during the extraction processes using the papain protease.

Absorption of vitamin B12

Once introduced into the body with food, when it arrives in the stomach, acid pH and pepsin detach cobalamin from the protein it was bound to. Cobalamin here then binds to cobalophylline, a glycoprotein found in saliva. When it arrives in the duodenum, the proteases of the pancreas separate cobalophylline and cobalamin, thanks to the alkaline environment.

At this point the cobalamin binds to the intrinsic factor, a glycoprotein that is released from stomach cells. The complex formed by vitamin B12-intrinsic factor is recognized by specific receptors present on the enterocytes of the ileum. The cobalamin thus enters the intestinal cells and passes through them, detaching itself from the intrinsic factor and being released outside.

Here it reaches the tissues, binds to other proteins (transcobalamin I and transcobalamin II) and the new complex thus formed is recognized by other receptors that allow the vitamin to enter the cells. Vitamin B12 also comes stored in large quantities in the liver.

One last consideration: the cobalt atom contained in hydroxocobalamin is not active. To become such an enzyme must intervene to obtain 5-deoxyadenosylcobalamin.

What is cobalamin used for?

Vitamin B12 is involved in several metabolism:

  • amino acids
  • nucleic acids (together with folic acid it allows the synthesis of DNA and RNA)
  • fatty acids

It is also very important for the production of Red blood cells and proper functioning of the bone marrow. His daily nutritional requirement is quite low: optimal values they are comprised between 2 – 2,5 µg. However, there are variations depending on age, the presence of other diseases or the presence of one pregnancy. In the latter case, the need usually increases, as for vitamin C and especially folic acid.

It often happens to find low levels of vitamin B12 in the elderly over 65. It is not known exactly why, but it has been hypothesized either a change in eating habits (often the elderly tend to eat less meat) or damage to the gastrointestinal mucosa with impaired absorption capacity.

A cobalamin supplementation could be indicated by the doctor in case of specific dietary deficiencies, therapy of pernicious anemia, prevention of vitamin B12 deficiencies in alcoholics and hyperhomocysteinemia.

Cobalamin e omocysteine

In case of iperomocisteinemia, the intake of folic acid, vitamins B12 and B6 has been shown to be effective in reducing plasma homocysteine ​​values.

Regular intake of vitamin B12 with nutrition and maintaining an active lifestyle are sufficient elements to maintain the right concentration of cobalamin in the blood. The dosage of vitamin B12 is among the laboratory tests that are prescribed with that of folate and homocysteine ​​to check, in case of diagnostic suspicion, the state of this important metabolic pathway.

An excess of vitamin B12 is detected above all when cobalamin is present in an inactive form and this happens above all in patients who follow a strictly vegetarian diet rich in algae.

The cross-examination with the detection of the folic acid concentration helps to understand whether the homocysteine ​​metabolism is in control or not: in the case of high cobalamin and normal folic acid, it is very likely that the excess cobalamin is in the inactive form .

Cobalamin is also high in obesity, diabetes, kidney and liver failure and some forms of leukemia.

Foods rich in vitamin B12

vitamin b12 and liver
Source: Pixabay

They are mainly the animal food to be particularly rich in vitamin B12. Among the foods that contain the most cobalamin we include:

  • liver
  • clams
  • some types of fish
  • milk and derivatives
  • beef
  • egg

For this reason above all i vegans must or assume vitamin B12 supplements in order not to run into deficiencies or to use foods with added cobalamin. With regard to vegetables and vegetables contain very little vitamin B12. Traces can be found in algae, soy derivatives or brewer’s yeast, however too little to cover daily nutritional needs.

Walnuts, almonds or sunflower seeds contain a little more, but usually whoever makes one vegetarian or vegan diet tends to use supplements or foods added with this vitamin to cover the needs.

Furthermore, the bioavailability of the vitamin: that contained in vegetables, in fact, in addition to being very scarce, is not assimilable by our body.

Vitamin B12 content in some foods

This is the vitamin B12 content in some foods:

  • Bovine liver: 60-65 µg / 100 grams
  • Lamb liver: 35 µg / 100 grams
  • Mussels: 19 µg / 100 grams
  • Sardine: 11,9 µg/100 grammi
  • Mackerel: 8 µg / 100 grams
  • Milk chocolate: 7.9 µg / 100 grams
  • Egg (yolk): 4.9 µg / 100 grams
  • Salmon: 4 µg / 100 grams
  • Egg (whole): 2.5 µg / 100 grams
  • Tuna in oil: 2.2 µg / 100 grams
  • Mozzarella: 2.1 µg / 100 grams
  • Emmenthal: 2 µg/100 grammi
  • Parmesan: 1.9 µg / 100 grams
  • UHT milk: 0.4 µg / 100 grams

Vitamin B12 deficiency: symptoms


The vitamin B12 deficiency it is usually linked to diseases that damage the parietal cells of the stomach or to a lack of dietary introduction, as happens in anorexic subjects or those who undergo diets without meat, fish and shellfish. Even chronic diseases such as Crohn’s disease they can cause deficiency symptoms.

Vitamin B12 deficiency causespernicious anemia which has like symptoms:

  • megaloblastic anemia (can also be caused by folic acid deficiency: it is important to make a differential diagnosis)
  • epatomegaly
  • splenomegalia
  • weight loss
  • abdominal pain
  • rarely glossitis
  • neurological symptoms (demyelinating or peripheral axonal neuropathies, reduced sensitivity of the limbs, muscle weakness, hyporeflexia in the initial stages. Then later spasticity, postural deficits and ataxia appear)
  • irritability
  • depression
  • paranoia
  • delirium
  • mental confusion
  • orthostatic hypotension

Excess of cobalamin: symptoms

Difficult to see symptoms of excess vitamin B12: usually exaggerated amounts of cobalamin are eliminated in the urine and sweat, without causing toxicity either side effects. Symptoms from overdose reported in the medical literature can be:

  • tremors
  • edema
  • nervousness
  • insomnia
  • tachycardia
  • kidney problems

As regards the cause which lead to an uncontrollable increase in cobalamin values ​​in the blood, must be sought in the abuse of certain foods but also in the intake of supplements exceeding the recommended doses. The choice of resorting to cobalamin supplements must always be supported by the opinion of the attending physician, who will evaluate the dietary intake and the actual reference values.

What do you need to know about vitamin B12?

The vitamin B12 it is a vital vitamin for the proper functioning of the human body. Normally it is introduced with the diet: gli fleshy food, fish, shellfish, milk and its derivatives are very rich in eating these foods get vitamin B12 naturally. Vegetables and vegetables, on the other hand, contain very little cobalamin. For this reason, if you decide to go on a vegetarian or vegan diet, ask your doctor or nutritionist how to supplement it. There are, in fact, many vitamin B12 supplements: ask your doctor what the improve.

Source: GreenStyle by

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