Vitamin B12 (also called cobalamin) is a water-soluble vitamin of the B complex with a unique feature: it is present exclusively in foods of animal origin, which makes its supplementation relevant for people on a vegetarian or vegan diet. It contributes to normal energy-yielding metabolism, to the normal functioning of the nervous system, to the normal formation of red blood cells, to the reduction of tiredness and fatigue and to another 4 physiological functions officially authorised at European level. This page covers how it works, the commercial forms (cyanocobalamin, methylcobalamin, hydroxocobalamin), the studied doses and where it fits within the Pleniage portfolio.
What is vitamin B12?
Vitamin B12, chemically cobalamin (its name comes from the fact that it contains a cobalt atom at the centre of its molecular structure), is a water-soluble vitamin of the B complex. It is the only vitamin that contains a metal in its structure and the most chemically complex of all the vitamins.
It has a unique feature in human nutrition: it is present exclusively in foods of animal origin. Plants do not produce B12; the vitamin is synthesised solely by bacteria and archaea, which then enter the food chain through animals that consume or harbour them. This makes B12 the only vitamin that requires specific attention in strict vegetarian and, above all, vegan diets.
The human body stores B12 in the liver in relatively large amounts (enough for several years in a person with adequate reserves), which explains why clinical deficiency usually appears years after dietary intake ceases, not immediately.
What is it for? Functions authorised at European level
At European level, the EFSA (European Food Safety Authority) has officially authorised eight health claims for vitamin B12. These claims may be used in the labelling and communication of food supplements that provide at least 15% of the nutrient reference value (NRV) per recommended dose.
Normal energy-yielding metabolism
Vitamin B12 contributes to normal energy-yielding metabolism (authorised EFSA claim, ID 95). This function reflects its role as a cofactor for enzymes in the catabolism of odd-chain fatty acids and of amino acids such as methionine.
Reduction of tiredness and fatigue
Vitamin B12 contributes to the reduction of tiredness and fatigue (authorised EFSA claim, ID 99). This function is related to normal energy-yielding metabolism and to the formation of red blood cells (adequate oxygenation of tissues).
Normal functioning of the nervous system
Vitamin B12 contributes to the normal functioning of the nervous system (authorised EFSA claim, ID 96) and to normal psychological function (authorised EFSA claim, ID 100). It is involved in the synthesis and maintenance of myelin, the sheath of the nerves. Prolonged B12 deficiency can produce significant neurological alterations (paraesthesia, gait disturbances, cognitive changes).
Normal formation of red blood cells
Vitamin B12 contributes to the normal formation of red blood cells (authorised EFSA claim, ID 98). Severe B12 deficiency produces a characteristic type of anaemia (megaloblastic anaemia), reversible once intake is corrected.
Other authorised functions
- Normal homocysteine metabolism (authorised EFSA claim, ID 97): together with folate and vitamin B6, B12 takes part in the remethylation cycle of homocysteine.
- Normal function of the immune system (authorised EFSA claim, ID 102).
- Process of cell division (authorised EFSA claim, ID 101).
How it works: the methyl cycle and methionine synthase
Vitamin B12 carries out its main function as an enzymatic cofactor for two human enzymes:
- Methionine synthase: an enzyme of the methyl cycle. It takes a methyl group from 5-methyltetrahydrofolate (the active form of folate) and transfers it to homocysteine to regenerate methionine, an essential amino acid. Without enough B12 this step is blocked, homocysteine accumulates (a documented cardiovascular risk factor) and folate becomes trapped in its methylated form (the methyl trap), unable to take part in other pathways.
- Methylmalonyl-CoA mutase: a mitochondrial enzyme of the catabolism of odd-chain fatty acids and of some amino acids. Without B12, methylmalonic acid accumulates, a clinical biomarker used to diagnose B12 deficiency.
The synergy with folate (vitamin B9) is direct and biochemically obligatory: B12 releases folate from its methylated form so that it can take part in the synthesis of purines and pyrimidines (components of DNA). Deficiency of either vitamin (B12 or folate) produces similar alterations in DNA synthesis and manifests as megaloblastic anaemia.
Dietary sources and at-risk populations
Vitamin B12 is present exclusively in foods of animal origin:
- Shellfish and molluscs (mussels, clams, oysters): the densest sources (cooked mussels up to 24 μg/100 g, almost 10 times the NRV).
- Animal offal (beef or lamb liver): very high content.
- Oily fish (tuna, salmon, sardines, mackerel).
- Red meat (beef, lamb) and white meat (chicken) in lower concentration.
- Eggs, especially the yolk.
- Dairy products (milk, yoghurt, cheese).
The nutrient reference value (NRV) in the European Union for vitamin B12 is 2.5 μg/day (micrograms per day, according to EU Regulation 1169/2011). A varied omnivorous diet easily covers this amount.
The populations at greatest risk of deficiency include:
- People on a strict vegetarian and vegan diet: absence or very reduced intake of dietary B12.
- People over 60-70 years of age: age-related gastric atrophy reduces the production of intrinsic factor and of hydrochloric acid, both necessary for B12 absorption.
- People on chronic treatment with proton pump inhibitors (PPIs) or H2 antagonists: they reduce the gastric acidity needed to release B12 from dietary proteins.
- People on prolonged treatment with metformin (type 2 diabetes): metformin can reduce B12 absorption over the long term.
- People who have had gastric surgery (bariatric, gastrectomy): total or partial loss of the ability to absorb B12 via intrinsic factor.
- People with pernicious anaemia: an autoimmune disease against intrinsic factor; it requires specialised medical supervision.
- People with chronic digestive diseases (Crohn's disease, uncontrolled coeliac disease): intestinal malabsorption.
Deficiency: signs, prevalence and diagnosis
Subclinical B12 deficiency is common in the at-risk populations mentioned, especially in people over 60-70 years of age (estimates close to 10-15% in some European cohorts) and in vegetarians without adequate supplementation. Frank clinical deficiency is less common but clinically relevant.
Signs and symptoms
The signs may be non-specific at the outset (persistent tiredness, irritability, pallor) and progress to more specific manifestations: megaloblastic anaemia (blood test showing macrocytosis), paraesthesia (tingling in the hands and feet), disturbances of balance and gait, cognitive impairment, glossitis (inflamed tongue).
Laboratory diagnosis
The usual tests are:
- Serum vitamin B12: initial screening. Very low values (<200 pg/mL) confirm deficiency.
- Holotranscobalamin (active B12): a more specific marker of functionally available B12.
- Methylmalonic acid (MMA) and homocysteine: functional biomarkers that rise in deficiency and are more sensitive than serum B12 for detecting incipient deficits.
The diagnosis and treatment of B12 deficiency fall within the medical domain. Maintenance supplements are intended for populations of known risk (vegetarians, older adults) and for general nutritional support within B complexes; therapeutic doses in diagnosed deficiency are significantly higher and must be prescribed under medical supervision.
Studied doses and commercial forms
The European NRV of 2.5 μg/day is covered by any varied omnivorous diet. B complex supplements typically provide between 10 and 1000 μg of B12 per dose (several times the NRV). Oral bioavailability is paradoxical: at physiological doses (2-5 μg) absorption depends on gastric intrinsic factor and is limited to 1-2% of the dose; at very high doses (≥1000 μg) a small fraction is absorbed by passive diffusion without requiring intrinsic factor, which is why high-dose B12 supplements can be effective even in people with malabsorption.
| Form | Characteristics | Notes |
|---|---|---|
| Cyanocobalamin | Stable synthetic form, the most widely used in supplementation and fortification | The body converts it into active forms. Low cost, high stability. |
| Methylcobalamin | Active coenzyme form of methionine synthase | Already active, requires no metabolic conversion. The natural form in foods. |
| Hydroxocobalamin | Storage form and the usual form in medical injectables | Longer plasma half-life. Common clinical use. |
| Adenosylcobalamin | Active coenzyme form of mitochondrial methylmalonyl-CoA mutase | Lower commercial availability. |
B12 in vegetarian and vegan diets
This section deserves an explicit statement because of its practical relevance.
Strict vegetarian diets and, especially, vegan diets require specific attention to B12 intake. B12 is not naturally present in foods of plant origin in nutritionally relevant amounts: algae (including spirulina) contain inactive analogues of B12 that are NOT usable by the human body and may even interfere with analytical detection. The only reliable plant sources of B12 are plant foods fortified with synthetic B12 (some plant drinks, fortified nutritional yeast, fortified cereals) or, most reliably, oral supplementation.
The recommendations of the main nutrition organisations (Vegan Society, Academy of Nutrition and Dietetics) agree: vegans should supplement with B12 on a regular basis. The usual regimens are 2,000-2,500 μg/week in a single dose or 25-100 μg/day. Synthetic cyanocobalamin is the standard form used in vegan supplementation because of its stability and low cost. This is one of the few situations in which supplementation with an isolated nutrient is essential, not optional.
Safety and interactions
Vitamin B12 has a very favourable safety profile. EFSA has not established a tolerable upper intake level (UL), considering it unnecessary; being water-soluble, the excess is eliminated in the urine and no toxic effects have been documented at the doses used in oral supplementation, even at very high doses (≥1000 μg/day).
Relevant drug interactions
- Proton pump inhibitors (PPIs) (omeprazole, esomeprazole, pantoprazole) and H2 antagonists (ranitidine, famotidine): they reduce the gastric acidity needed to release B12 from dietary proteins. Chronic treatments may induce a functional deficit.
- Metformin (type 2 diabetes): prolonged treatment may reduce B12 absorption.
- Antibiotics (chloramphenicol, others): they may interfere with the haematological response to B12.
- Oral contraceptives: a modest effect on plasma levels.
- Chronic alcoholism: malabsorption and increased consumption.
How to choose a B12 supplement
- Form according to objective: cyanocobalamin for general use (stable, inexpensive, extensively studied); methylcobalamin if you are looking for the directly active form; hydroxocobalamin as an injectable under medical prescription.
- Dose consistent with the profile: 25-100 μg/day for general maintenance; 1000 μg/week or 100-250 μg/day for vegetarians/vegans; higher therapeutic doses ONLY under medical prescription.
- Sublingual form: some commercial supplements are sublingual, which can be useful in people with intestinal malabsorption (the sublingual mucosa allows some direct absorption).
- Consistency with the B complex: supplementation with B12 alone is rarely indicated (except in vegetarians/vegans); the consistent approach is as part of a B complex.
Vitamin B12 in the Pleniage portfolio
In the formulation of PLENIAGE® ENERGY PRO, vitamin B12 is part of the complete B complex (B1, B2, B3, B5, B6, B12) that is incorporated together with magnesium citrate, alpha-lipoic acid (175 mg), vitamin C, vitamin E and biotin. The formula is designed to provide the B-group vitamins in a coordinated way, in synergy with cofactors and antioxidants involved in cellular energy metabolism. Each ingredient is backed by individual scientific research and, in the case of the B complex vitamins, by claims officially authorised at European level; the specific combination of this formula has not been the subject of its own clinical trial.
This page is part of the Energy and performance cluster. To explore other related components in more depth, see the Folic acid (vitamin B9) page (direct biochemical synergy in the methyl cycle) and the Vitamin B5 page.
Frequently asked questions about vitamin B12
What are cyanocobalamin and methylcobalamin?
They are two different forms of vitamin B12. Cyanocobalamin is a very stable synthetic form, widely used in supplementation and food fortification; the body converts it into active forms. Methylcobalamin is the active coenzyme form of the enzyme methionine synthase, usable directly without conversion. Both are valid for supplementation; cyanocobalamin is the standard form because of its stability and low cost.
Do vegetarians and vegans need to supplement with B12?
Yes, especially vegans. Vitamin B12 is present exclusively in foods of animal origin; plants do not produce it. The B12 analogues present in algae (including spirulina) are NOT functionally usable by the human body. The recommendations of the main nutrition organisations (Vegan Society, Academy of Nutrition and Dietetics) agree: regular B12 supplementation is necessary in vegan diets and strongly advisable in strict vegetarian diets. Usual regimens: 2,000-2,500 μg/week in a single dose, or 25-100 μg/day.
How much vitamin B12 do I need per day?
The NRV in the European Union is 2.5 μg/day, an amount covered by any varied omnivorous diet. For maintenance in omnivores, B complex supplements usually provide 10-25 μg of B12. For vegetarians and vegans: 25-100 μg/day or 1,000-2,500 μg/week. Therapeutic doses in diagnosed deficiency are significantly higher and must be prescribed under medical supervision.
Does B12 have side effects?
It has a very favourable safety profile. EFSA has not established a tolerable upper intake level; being water-soluble, the excess is eliminated in the urine. Isolated cases of skin rashes have been described at very high doses (rare). No toxic effects have been documented at the usual supplementation doses.
Why can metformin or omeprazole lower my B12 levels?
Through different mechanisms, but both relevant to chronic treatment. Metformin (type 2 diabetes) can reduce the intestinal absorption of B12 over the long term; people on prolonged metformin treatment should periodically monitor their B12 levels. Proton pump inhibitors (omeprazole and similar) reduce gastric acidity, which is needed to release B12 bound to dietary proteins; chronic treatment may induce a functional deficit.
Why are older adults at greater risk of B12 deficiency?
Age-related gastric atrophy reduces the production of intrinsic factor (a gastric protein needed for the intestinal absorption of B12) and of hydrochloric acid (needed to release B12 from dietary proteins). Estimates close to 10-15% of people over 60-70 years of age in European cohorts have subclinical B12 deficiency. Supplementation with synthetic B12 (which does not require dietary proteins to release it) is a common nutritional support option in this population.
How is B12 deficiency diagnosed?
Through laboratory tests. Serum B12 is the initial screening; holotranscobalamin (active B12) is more specific to functionally available B12. The most sensitive functional biomarkers are methylmalonic acid (MMA) and homocysteine, which rise in deficiency even when serum B12 still appears within range. Diagnosis and treatment fall within the medical domain.
Vitamin B12 (cobalamin) is a water-soluble vitamin of the B complex with a unique feature: it is present exclusively in foods of animal origin. It has eight authorised "green" EFSA claims (energy-yielding metabolism, nervous system, formation of red blood cells, reduction of tiredness and fatigue, homocysteine metabolism, psychological function, immune system, cell division). Its central role is to act as a cofactor for two human enzymes involved in the methyl cycle and in mitochondrial catabolism. People on a strict vegetarian and vegan diet require regular supplementation; people over 60-70 years of age, chronic treatments with PPIs or metformin and gastric surgery are situations of deficiency risk worth keeping in mind.
At PLENIAGE® we publish scientific content on evidence-based supplementation. You can explore the Energy and performance cluster for more related pages and articles.
References
The statements in this article are based on the available scientific literature and on the health claims officially authorised by EFSA.
- EFSA Health Claims Register — vitamin B12: authorised claims ID 95 (energy-yielding metabolism), 96 (nervous system), 97 (homocysteine metabolism), 98 (formation of red blood cells), 99 (tiredness and fatigue), 100 (psychological function), 101 (cell division), 102 (immune system). Official source: EU Register of Nutrition and Health Claims.
- EU Regulation 1169/2011 on food information to consumers — Annex XIII (NRV for B12: 2.5 μg/day).
- Pawlak R, Parrott SJ, Raj S, Cullum-Dugan D, Lucus D. How prevalent is vitamin B(12) deficiency among vegetarians? Nutr Rev. 2013;71(2):110-117. PMID: 23356638.
- Aroda VR, Edelstein SL, Goldberg RB, et al. Long-term Metformin Use and Vitamin B12 Deficiency in the Diabetes Prevention Program Outcomes Study. J Clin Endocrinol Metab. 2016;101(4):1754-1761. PMID: 26900641.
- Lam JR, Schneider JL, Zhao W, Corley DA. Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. JAMA. 2013;310(22):2435-2442. PMID: 24327038.
- Smith AD, Smith SM, de Jager CA, et al. Homocysteine-lowering by B vitamins slows the rate of accelerated brain atrophy in mild cognitive impairment: a randomized controlled trial. PLoS One. 2010;5(9):e12244. PMID: 20838622.