Table of Contents
What’s this
Vitamin B12 (called cyanocobalamin due to the presence of a cobalt atom inside the molecule) was discovered during studies on pernicious or megaloblastic anemia, a form of anemia characterized by the presence of red blood cells larger than normal and by the simultaneous degeneration of the Central Nervous System.
Back in 1926, in the context of studies on pernicious anemia, it was discovered that one liver rich diet stimulated the synthesis of red blood cells. Only several years later, in 1948, was vitamin B12 extracted from the liver. It was then understood that the factor capable of resolving the pathology was just vitamin B12. In 1964 the Nobel Prize was awarded to Dorothy Hodgkin who determined the molecular structure of vitamin B12. This molecular structure is shared by a group of chemically related organic substances collectively known as cobalamin.
What is it for
Vitamin B12 is involved in the metabolism of amino acids, nucleic acids (DNA and RNA) and fatty acids. For these basic functions it plays a fundamental role in production of red blood cells.
Metabolism
Vitamin B12, present in foods of animal origin, it is found bound to proteins. In order for it to be absorbed, the first step consists in the division of vitamin B12 from the proteins to which it is bound, an operation that is performed in the stomach by some enzymes called proteases.
Transport at the level of the duodenum, the first part of the intestine, then, occurs through specific transporters called R-binder: these are salivary and food proteins that have a high affinity for vitamin B12. Once bound to the R-binder, vitamin B12 is transported to the level of the duodenum. Here the alkaline environment and the presence of other enzymes (pancreatic proteases) cause the vitamin B12 to separate from the R-binder proteins and bind to the intrinsic factor (Intrinsic Factor, IF).
The intrinsic factor is a glycoprotein (ed. a protein containing carbohydrates) which is produced by cells of the mucous membrane of the gastric fundus: the complex formed by vitamin B12 and intrinsic factor it reaches the level of the last tract of the small intestine, where a specific receptor is present. The binding with this receptor serves to carry the complex vitamin B12 + intrinsic factor inside the cells that line the intestine, the enterocytes.
It is through this modality that we are able to absorb vitamin B12 present in the food we eat. Vitamin B12 is so important that there are reservations inside the body. The main accumulation site is represented from the liver and kidney. Total reserves are approximately 2 or 3 mg.
Where is it
Vitamin B12 is synthesized by microorganisms and algae and would therefore be completely absent in foods of plant origin, where it appears only secondary to bacterial contamination.
What are foods rich in vitamin B12?
- The largest amounts of vitamin B12 are found in offal and in the liver (up to 110 micrograms per 100 grams of product).
- Discrete contents of vitamin B12 are found in fish, molluscs, crustaceans, egg yolk, parmesan.
- Meat and milk they have lower amounts of vitamin B12 (about 2 micrograms per 100 grams).
- The food industry has taken care of fortify with the addition of vitamin B12 some foods, especially cereals.
- Some seaweed used in cooking they are also the basis of food supplements intended for the vegan population.
People mostly a risk of shortage they are the elderly, vegetarians, but above all vegans and people suffering from chronic-degenerative diseases (such as gastritis on an autoimmune basis).
The blood concentrations of vitamin B12 and in general of all the B vitamins in smokers they are significantly lower than non-smokers.
Shortage
The determination of the levels of vitamin B12 is an insensitive indicator since, even in the case of inadequate intake, the levels in the blood of this vitamin can remain normal for a long time. This happens because the body fetches vitamin B12 from reserves. To highlight a possible vitamin deficiency it is therefore necessary to resort to other indicators.
A high plasma level of methylmalonic acid is a sensitive and specific parameter because it represents the first sign of deficiency of vitamin B12 even when clinical signs are not yet present. Unfortunately, the method that allows to evaluate the plasma levels of methylmalonic acid has high costs and for this reason it is not very applicable at the clinical level.
Another good indicator of the state of shortage is the mean cell volume of red blood cells since in deficiency of vitamin B12 i Red blood cells they are small in number but have a greater volume than the physiological condition.
Symptoms
Vitamin B12 deficiency it manifests itself slowly in time. This happens because i deposits of vitamin in the liver are able to support the daily requirement for a time that goes from 3 to 5 years.
The main cause of vitamin B12 deficiency is the malabsorption and the best known clinical form is thepernicious anemia linked to a lack of intrinsic factor. Gastric resection, atrophic gastritis, Crohn’s disease, celiac disease and alcoholism can be among the causes of vitamin B12 deficiency.
There are undoubtedly among the groups of populations most at risk seniors, in which a malabsorption linked to a poor digestion of proteins due to reduced production of hydrochloric acid in the stomach as is typical of atrophic gastritis. In industrialized countries, shortages related to food shortages are very rare but can manifest themselves especially in vegans.
Causes
The causes that lead to low vitamin B12 levels are:
- inadequate intake (elderly, vegetarians, vegans);
- reduced or lack of intrinsic factor production, as can occur in the case of total or partial gastrectomy or in the case of atrophic gastritis;
- decreased intestinal absorption, as is typical in patients with Crohn’s disease or celiac disease and in those who have undergone resection of the ileum;
- defect of vector proteins (R-binder, intestinal receptors);
- increased consumption, as occurs in late pregnancy.
Consequences
The clinic of a person with vitamin B12 deficiency is dominated by megaloblastic anemia and the appearance of neurological and gastrointestinal alterations.
THE neurological disorders they include paraesthesia (changes in sensitivity felt in the limbs and other parts of the body), disturbances in balance and polyneuritis (inflammation of the peripheral nerves resulting in malfunction). In the late stages, ataxia (lack of muscle coordination which makes it difficult to perform voluntary movements) and spasticity (excessive increase in muscle tone) can occur.
From gastrointestinal point of view appear glossitis (inflammation of the tongue that appears red and peeling), nausea, dyspepsia (i.e. indigestion), abdominal pain. In some cases, an increase in homocysteine levels in the blood may occur, although to a lesser extent than folate deficiency.
What to do
In case of vitamin B12 deficiency the first thing to do is investigate the presence of any pathologies which may be the cause. Following this, it will be necessary to increase the consumption of foods that contain it in greater quantities. Among these, as well liver, fish and shellfish fortified cereals and brewer’s yeast should be mentioned.
It is important to remember that with theexposure to heat most of the vitamins are lost. Similarly, the refining of flour and cereals leads to a loss of vitamins of group B: for this reason, in cases of vitamin B12 deficiency it is preferable to take whole and unprocessed products industrially.
Intake of vitamin B12 in ampoules or tablets it is to be reserved for patients suffering from megaloblastic anemia and vegans who struggle to cover their daily needs with diet alone.
Excess
The studies conducted so far highlight the lack of side effects associated with high vitamin B12 consumption in healthy individuals.
High Vitamin B12, What Does It Mean?
From a medical point of view, high levels of vitamin B12 are associated with pathological conditions such as neoplasms with liver metastases and acute and chronic liver diseases.
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