Vitamin B12 and Vegan Diet

Vitamin B12 and Vegan Diet


The vegan diet is a nutritional regime which, if not managed properly, can favor the establishment of certain nutritional deficiencies ; among the many “potentials”, we also find the chronic deficiency of vitamin B12 (cobalamin).

This is basically due to the exclusion of entire food groups which, in the diet of man – an omnivorous animal – perform functions that are very difficult to replace. It is certainly no coincidence that meat , fishery products and eggs on the one hand, and milk and derivatives on the other, are collected under what are defined as the first and second basic food groups .Below we will first try to understand the basics of the vegan diet, the general information on vitamin B12 , the risks attributable to a possible deficiency and, finally, how to prevent or cure the chronic deficiency of this very important nutrient .


What is veganism all about?

The vegan diet is a food philosophy based on the exclusive consumption of foods belonging to the plant kingdom (Plantae), bacteria (Bacteria) and mushrooms (Fungi).

It does not contemplate any part of the animal organism (meat, offal , etc.), eggs, secretions of all kinds and derivatives (milk and dairy products, honey , royal jelly , propolis , etc.). In addition to mammals, birds, fish, crustaceans , molluscs , insects and arachnids are obviously excluded – let’s not forget that in other parts of the world it is customary to consume these creatures too.

It also eliminates drugs, supplements and cosmetics obtained by means of animal testing or which contain ingredients that are not permitted – including excipients – silk and wool-based clothes, and vegetables grown using fertilizers of animal origin ( meal , blood , horns and bones beef, fish meal, etc.).

Vitamin B12

What is vitamin B12 and what is it for?

Vitamin B12 or cobalamin is a water -soluble B vitamin .

The biological roles of cobalamin are:

  • promote the transfer of an H (hydrogen) ion between two neighboring C (carbon) atoms of the same molecule;
  • reduction of ribonucleotides to deoxyribonucleotics;
  • transfer of a methyl group in the same molecule.

In the mammalian organism, this translates into very important functions:

  • synthesis of methionine from homocysteine ;
  • isomerization of methylmalonylCoA to SuccinylCoA.

Ultimately, in humans the vit. B12 is essential to various metabolic processes, with great involvement in:

  • DNA synthesis ;
  • fatty acid metabolism ;
  • synthesis of amino acids .

Ultimately, nerve tissue and erythrocytes ( red blood cells ) appear to have the greatest need for cobalamin.

This is why cobalamin is considered a nutrient of vital importance for the correct development of the central nervous system ( CNS ) of the embryo -foetus and for the erythropoiesis process (formation of red blood cell elements).

Vitamin B12 absorption

Vitamin B12 is not easily absorbed.

This is because it must first be bound to the salivary polypeptide R in the presence of gastric acid pH , which will then yield it to Castle’s intrinsic factor which is in turn necessary for absorption in the small intestine ( small intestine ) – not the colon .

Understanding this process is essential to understand “why”, contrary to herbivores that are also quite “close” to us from an evolutionary point of view, human beings must necessarily obtain vitamin B12 from foods of animal origin.

Where is vitamin B12 “normally” found?

The production of vitamin B12 (in its natural forms of methylcobalamin and adenosylcobalamin ) is the exclusive prerogative of some unicellular organisms such as bacteria and archae.

Mushrooms lack the ability to synthesize cobalamin.

Note : the vit. B12 synthetically and used in dietary supplements is of the hydroxocobalamin or cyanocobalamin type .

Only by “climbing” the food chain does cobalamin reach the tissues of herbivorous animals – and then, of course, carnivores – from the microorganisms that produce it.

For carnivores and omnivores, the primary nutritional source of vitamin B12 is muscle meat and organs, particularly liver . Useful levels are found in milk and eggs, although bioavailability is lower in the latter.

But how? In different ways.

Some herbivores, such as rabbits , after feeding, process the first hard stools rich in bacterial flora that elaborate vitamin B12. Later they feed on it, absorbing the cobalamin and expelling the final feces .

The bacterial flora present in the human colon also produces a certain level of cobalamin. However, seen and considered the complicated process of absorption of the same – which must take place in the small intestine and involves the intervention of saliva and gastric secretions – we can say with certainty that this cannot constitute a considerable nutritional source.

Herbivores with multiple stomachs possess a particular gastric bacterial flora responsible for the synthesis of cobalamin, which is subsequently absorbed in the intestine .

As for other herbivores that do not exploit these mechanisms, however, it is possible that they are able to reach their vitamin B12 requirements thanks to the bacterial film naturally present on food – given the immense amount of vegetables they are able to consume every day.

Some molecules such as corronoids are very similar to cobalamin but do not have the same biological activity. When taken with the diet, they can compete with vitamin B12 and impair its absorption.

B12 deficiency complications

Vitamin B12 deficiency should not be underestimated.

This deficit may be at the basis of an altered synthesis of nucleic acids , a cause of ominous complications for the embryo-foetus (especially of the CNS).

Children deficient in cobalamin show an impaired growth process.

In adults however, the lack of the right levels of cobalamin can lead to the onset of weakness, pernicious anemia and nervous complications. It is often the reason for hyperhomocysteinemia , which some studies have evaluated as an independent cardiovascular risk factor .

Older adults with chronic vitamin B12 deficiency may be more prone to neurological and cognitive decline.

The causes of the deficiency can be substantially 2:

  • Inadequate dietary intake: typical of vegan regimes that are not well organized and integrated;
  • Impaired absorption: due to gastric complications ( achlorhydria , gastric resection, etc.) or intestinal complications of the small intestine (resection of the small intestine, chronic inflammatory diseases, etc.) or due to the intake of certain drugs.

Note : as we have said, taking molecules similar to cobalamin (for example from algae ) which are not biologically active can compromise the absorption of the biologically active one.

How Much Do You Need

Vitamin B12 requirement

The estimated average requirement (EAR) for vitamin B12 for women and men 14 years and older is 2.0 μg/day. The recommended dietary allowance (RDA), on the other hand, is 2.4 μg / day.

The RDA for pregnancy equals 2.6 μg/day and for lactation it equals 2.8 μg/day

The RDA for children up to 12 months of adequate intake (AI) is 0.4-0.5 μg / day.

The RDA for children aged 1 to 13 years, the RDA increases with age from 0.9 to 1.8 μg / day.

Also, because 10 to 30 percent of older people may not be able to effectively absorb naturally occurring cobalamin in food, those over 50 are advised to use vitamin B12-fortified foods or a supplement.

The European Food Safety Authority (EFSA) uses the population reference intake (PRI) instead of RDA and sets the AIs as follows:

  • for women and men aged > 18 years 4.0 μg / day;
  • for pregnancy 4.5 μg / day;
  • for lactation 5.0 μg / day;
  • for children aged 1 to 17 years, AIs increase with age from 1.5 to 3.5 μg/day.


How to find out if the vegetarian diet is not rich enough in vitamin B12

The first step is undoubtedly to understand if our body has enough vitamin B12 available.

The most widespread analysis is the blood dosage of total circulating vitamin B12 even if, as some investigations have shown, this does not always reflect the true picture of the situation.

We know that a B12 deficiency correlates with an increase in homocysteine ​​in the blood. On the other hand, it has been shown that very high levels of folate (typical of vegetarian diets) can compromise this correlation, hiding the cobalamin deficiency.

Instead, other tests seem more sensitive, such as, for example, the dosage of specific markers; for example the active molecular form of the vitamin, bound to a transporter, or metabolites of incomplete lipid degradation.

Vegan remedies for possible vitamin B12 deficiency

The only reliable vegan sources of vitamin B12 are foods fortified with synthetic vitamin B12 and dietary supplements .

Among the enriched or fortified foods we mention:

  • some vegetable drinks used as milk substitutes (so-called plant milks );
  • some soy -based products (most frequently fermented ones, such as tofu , tempeh , miso );
  • some breakfast cereals . _

Most vegans who use fortified or enriched foods and/or specific dietary supplements get enough cobalamin.

However, a few more words should be spent on the use of fortified foods. To make sure you’re getting enough vitamin B12, it’s always a good idea to check food labels carefully . Knowing the cobalamin content per 100 g, it will therefore be possible to make an approximate calculation of the amount of vitamins introduced based on the total portions.

For example, if a fortified soymilk contains 1 μg of B12 per serving (e.g. 125-150 mL), consuming about 3-4 servings per day may be more or less sufficient. If more enriched foods are present in our diet, the risk of deficiency would be drastically reduced.

In principle, however, the use of supplements is safer and cheaper.



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