Vitamin B₁₂ Facts

Vitamin B₁₂ is an essential vitamin that performs many important functions in the body. It is exclusively formed by microorganisms and must be ingested through food or dietary supplements. ProVeg explains how vegans and vegetarians can protect themselves against a shortage of vitamin B₁₂.

What is vitamin B₁₂?

The term vitamin B₁₂ is an umbrella term for the group of substances called cobalamins.¹ Of these cobalamins, methylcobalamin and 5’‑deoxyadenosylcobalamin are the only two bioactive forms of vitamin B₁₂, and act as coenzymes in the body.² Two other cobalamins – hydroxocobalamin and aquacobalamin – are not coenzyme forms of vitamin B₁₂ themselves but can be converted by the body into one of the two active cobalamins. The same applies to synthetically produced cyanocobalamin, which is used for most vitamin B₁₂ supplements.³ However, metabolic or genetic disorders, as well as a lack of nutrients, can impair the conversion process.⁴ Cobalamins can only be produced by microorganisms such as bacteria.⁵

Functions of vitamin B₁₂

The two coenzyme forms of vitamin B₁₂ are essential components of two endogenous enzymes that occur in all cells and are involved in many metabolic reactions. Vitamin B₁₂ plays an important role in the reproduction of DNA in cells as well as in the formation of new proteins. It also influences the nervous system’s overall health, the energy production of the cells, and the synthesis of the red blood protein haemoglobin.⁶

Vitamin B₁₂ deficiency: symptoms and medical consequences

A lack of cobalamin leads to disturbances in cell division across the entire body. This mainly affects the formation of red blood cells, but also impacts on the oral and pharyngeal mucosa, as well as on the nervous system. A typical symptom of vitamin B₁₂ deficiency is a form of anaemia which causes the red blood cells to become abnormally enlarged (megaloblastic anaemia). Characteristic signs include pale skin and mucous membranes and the regression of oral, tongue, and intestinal mucosa, as well as the subsequent impairment of nutrient uptake, along with non-specific symptoms such as general weakness, rapid fatigue, and dizziness.^7 8 An insufficient supply of vitamin B₁₂ also leads to increased blood concentrations of homocysteine, which represents a risk factor for the development of atherosclerosis and cardiovascular diseases.

The second set of symptoms caused by a deficiency in cobalamin is even more serious. These include damage to the central nervous system, which can manifest itself as sensory disorders (such as the feeling of ‘pins and needles’ in hands, feet, and other parts of the body), a lack of appetite, delayed reflexes, and reduced motor abilities, as well as impairments in movement coordination. Mental disorders, ranging from confusion or memory problems to psychoses and hallucinations, can also be signs of vitamin B₁₂ deficiency.^9 10 Both sets of symptoms can occur independently of each other.

Daily requirements of vitamin B₁₂

While the recommendations for B₁₂ intake vary between regions, the following daily doses are being recommended by the European Food Safety Authority (EFSA) for people on a Western diet:¹¹

• Infants: 1.5 micrograms
• Children, aged 1 to 6: 1.5 micrograms
• Children, aged 7 to 10: 2.5 micrograms
• Children, aged 11 to 14: 3.5 micrograms
• People over 14 years of age: 4 micrograms
• During pregnancy: 4.5 micrograms
• When breastfeeding: 5 micrograms

Absorption of vitamin B₁₂

Foods of animal origin are exposed to gastric acid in the stomach, which facilitates the extraction of vitamin B₁₂ from the proteins to which it is bound. Food supplements, on the other hand, contain cobalamin in the free form of the molecule, with the absorption of vitamin B₁₂ taking place in the lower small intestine, where it is bound to a special transport molecule, the so-called ‘gastric intrinsic factor’. This ‘gastric intrinsic factor’ is a glycoprotein which transports vitamin B₁₂ to special receptors in the intestinal mucosa through which it then reaches the mucosal cells. However, the number of gastric intrinsic factor receptors is limited. Approximately 56% of an oral dose of 1 microgram of vitamin B₁₂ is absorbed, but absorption decreases dramatically when the capacity of the intrinsic factor is exceeded. It is estimated that the absorption capacity of cobalamin is 1.5-2 micrograms per meal.¹² Only after a few hours have passed are the receptors able to absorb further vitamin B₁₂.^13 14

If vitamin B₁₂ is supplied in very large amounts via oral consumption (at least 200 micrograms), about 1-2% of the dose can enter the blood via passive diffusion through the intestinal wall.¹⁵ However, absorption through the oral mucosa (for example, taken under the tongue or dissolved in the mouth) is at least as effective as oral vitamin B₁₂ intake (swallowing directly). In the case of consumption via the oral mucosa, absorption also takes place via the intestinal wall due to partial swallowing, so long as the dose is sufficiently high.¹⁶

The intake of vitamin B₁₂ – starting at a minimum dose of 200 micrograms – can therefore be calculated as follows:*

Absorption (in micrograms) = 1.5 + dose/100

Approximately 60% of vitamin B₁₂ (2000-5000 micrograms) is stored in the liver, with the kidneys being another important storage reservoir.¹⁷ Full stores of vitamin B₁₂ in the body can suffice for 3-5 years.¹⁸

Causes of insufficient vitamin B₁₂ intake

Insufficient vitamin B₁₂ intake is caused mainly by the following:¹⁹

• Eating food which contains too little vitamin B₁₂ to cover daily requirements
• Bodily inability to properly utilise the absorbed vitamin B₁₂
• Higher usage of vitamin B₁₂ by the body than usual

Vitamin B₁₂ deficiency can also be caused by certain diseases. Chronic gastritis (inflammation of the gastric mucosa) or a gastrectomy (partial or total surgical removal of the stomach) can cause a deficit in the gastric intrinsic factor, which is crucial for the absorption of vitamin B₁₂.^20 21 The intake of vitamin B₁₂ through fortified foods and orally consumed food supplements is severely hindered in people with these conditions.²² A sublingual (under the tongue) or intramuscular supply of vitamin B₁₂ via injection is recommended in these cases (see section on vitamin B₁₂ supplements). Medication can also have a negative effect on the uptake of vitamin B₁₂.²³

Vitamin B₁₂ deficiency in the broader population

The major risk groups for vitamin B₁₂ deficiency are vegans (and some vegetarians), the elderly,²⁴ people with gastrointestinal diseases, and pregnant and nursing women²⁵ – as well as alcoholics and smokers.

In the United Kingdom and United States vitamin B₁₂ deficiency has been diagnosed in around 6% of people under 60 years, and around 20% in those older than 60 years. In Latin America, about 40% of children and adults suffer from some form of vitamin B₁₂ deficiency. And about 11% of vegans in the UK are affected by B₁₂ deficiency.²⁶

Vitamin B₁₂: Occurrence and bioavailability in food

Most food of animal origin contains vitamin B₁₂. To ensure a sufficient supply, animals such as pigs and chickens are given vitamin B₁₂ via fortified feed.^27 28 Ruminants may require to get additional cobalt (which is an important trace element and essential in the formation of vitamin B₁₂), via fortified feed, especially if there is a deficiency of cobalt in soils.^29 30 Occurrence in root and tuber vegetables or fermented foods such as sauerkraut and fermented soya products is possible, but not sufficient to make a significant contribution to vitamin B₁₂ supply. Opposing opinions are not scientifically supported.³¹

Some plant-based foods are enriched with cobalamin. These include various soya products, muesli, cornflakes, fruit juices, and meat alternatives. Depending on the vitamin B₁₂ content, vitamin B₁₂ uptake can be improved by consuming these fortified foods, but this will not always cover daily requirements.³² Furthermore, EU law regarding organic production of food prohibits enriching organic food with vitamin B₁₂. As such, organically-produced vegan food from EU countries does not contain cobalamin.³³

Vitamin B₁₂ test: blood markers used to determine vitamin B₁₂ levels

Due to the body’s capacity to store vitamin B₁₂  for long periods of time, it can take years for clinical symptoms of vitamin B₁₂ deficiency to become apparent. However, the long-term state of the body’s vitamin B₁₂ stores can be determined by means of blood analyses. Various test values concerning the cobalamin metabolism should be measured, especially holo-transcobalamin II (holo TC II). Solely testing for blood content of vitamin B₁₂ is not a suitable method for reliably assessing the state of the body’s supplies, since a functional vitamin B₁₂ deficiency may already be present in the body’s cells even when blood values for vitamin B₁₂ are normal. The earliest indicator of a deficiency is low holo TC II values. This transport protein binds to vitamin B₁₂ and makes it available to the body’s cells. The following table shows the reference range for holo TC II, which can be used to determine a vitamin B₁₂ deficiency:³⁴

If the holo TC II value alone is insufficient to determine whether a vitamin B₁₂ deficiency exists, values for homocysteine (on an empty stomach) and methylmalonic acid should be determined via blood serum in addition to holo TC II. A vitamin B₁₂ deficiency is indicated by increased levels of homocysteine (above 12 micromole/litre) and methylmalonic acid (above 260 nanomole/litre).³⁵ The problem with vitamin B₁₂-related anaemia is that it can be delayed or ‘masked’ by a high intake of folate – for example in vegetarian or vegan diets – because these vitamins collaborate in the process of cell division. At the same time, however, neurological changes will progress, possibly leading to permanent damage to the central nervous system.³⁶

Vitamin B₁₂ supply on a vegan/vegetarian diet

A vegetarian diet can provide an adequate supply of vitamin B₁₂. However, in various studies vegetarian participants consumed an average of only 1.7-2.5 micrograms of vitamin B₁₂ daily, which is slightly below the recommended amount.^37 38 If a vegan diet is not accompanied by dietary supplements or if an inadequate amount of vitamin B₁₂-enriched foods is eaten, the expected vitamin B₁₂ intake is 0 micrograms per day. Accordingly, in many studies vegans exhibit an insufficient supply of vitamin B₁₂.^39 40 41

Thus, when following a vegan/vegetarian diet, a sufficient supply of vitamin B₁₂ should be ensured through fortified foods and dietary supplements in the form of, for example, tablets, drops, or vitamin B₁₂ toothpaste. Pregnant and breastfeeding women should pay particular attention to consuming an adequate quantity of vitamin B₁₂ in order to ensure that their children receive a sufficient supply.

Vitamin B₁₂ supplements

Nutritional supplements for oral (pills, capsules) or sublingual (lozenges, drops, sprays) intake of vitamin B₁₂

The use of multivitamins is not recommended. If you have a nutrient deficiency or a special need, it’s best to supplement with that specific nutrient. However, stand-alone vitamin B₁₂ supplements can be highly effective. According to studies, there is no significant difference between a sublingual or oral intake of vitamin B₁₂.^42 43 The respective absorption rates for doses of 50 micrograms, 200 micrograms, and 1000 micrograms are approximately 1.5 micrograms, 3.5 micrograms, and 11.5 micrograms (see section on vitamin B₁₂ intake).

Vitamin B₁₂ toothpaste
One form of effective vitamin B₁₂ supplementation is the use of toothpaste enriched with vitamin B₁₂. A study has shown that it can significantly improve the vitamin B₁₂ status of people who have brushed their teeth with it twice a day for 12 weeks. The toothpaste in the study was enriched with 100 micrograms cyanocobalamin per gram.⁴⁴

Intramuscular vitamin B₁₂ injections
In most countries, intramuscular injections have long been the standard treatment for vitamin B₁₂ deficiency. However, the current data shows that oral and sublingual vitamin B₁₂ preparations are sufficient and may even be superior to intramuscular injections.⁴⁵ In patients suffering from pernicious anaemia (an autoimmune disease), intramuscular injection is the most efficient form of supplementation.

ProVeg tips for an optimal supply of vitamin B₁₂

• Vegans and vegetarians should have their vitamin B₁₂ levels checked regularly.
• People following a vegan diet should regularly take dietary supplements in order to ensure an adequate supply of vitamin B₁₂.
• To determine a suitable dosage, both vitamin B₁₂ requirements and the dose of the supplement must both be taken into account.

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