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Vitamin B12 and its importance in the vegetarian diet

Vitamin B12 and its importance in the vegetarian diet

Published: 12 May, 2022 | 8'

Vitamin B12 is essential to the overall diet as it helps to keep the nervous system and the number of red blood cells healthy.

It also helps prevent megaloblastic anaemia, a blood disorder that causes tiredness and weakness, and is involved in the formation of genetic material (DNA).

What is vitamin B12?

Also known as cobalamin, vitamin B12 is water-soluble and belongs to the group of B vitamins. Since it was discovered almost 65 years ago, it has been recognised as playing a central and beneficial role in the recovery from pernicious anaemia.

How is vitamin B12 absorbed?

Vitamin B12 in food must first be released through the action of saliva and then by gastric acid secretion in the stomach. The stomach cells secrete a so-called intrinsic factor (glycoprotein) which is essential to ensure that vitamin B12 is absorbed in the intestine.

The complex formed by vitamin B12 and intrinsic factor is absorbed in the ileum (part of the small intestine); this absorption is saturable at vitamin B12 doses of approximately 1.5 and 2.5 μg per meal. At intakes of around 1 μg around 50% is absorbed, at doses of around 25 μg only 5% is absorbed.3,4,7

What is the use of vitamin B12?

Vitamin B12 is involved in energy metabolism, especially fatty acid and amino acid metabolism, is essential for the production of folate and red blood cells, and helps the overall functioning of the nervous system.

The European Food Safety Authority (EFSA) confirms the following health-promoting properties of vitamin B12 which contributes to:

  • the normal formation of red blood cells.
  • normal functioning of the nervous system
  • energy metabolism
  • normal homocysteine metabolism.
  • the process of cell division.

Foods containing vitamin B12

The main sources of vitamin B12 are of animal origin and foods containing vitamin B12 are:

  • Fish (e.g. 0.03-0.1 mg/kg in salmon, 0.01-0.03 mg/kg in tuna), meat (e.g. 0.1 mg/kg in lamb), poultry, eggs, milk and other dairy products.
  • Clams and beef liver (0.1 mg/kg).
  • Some breakfast cereals, nutritional yeast and other food products enriched with vitamin B12.

Recommended daily intake of vitamin B12

The amount of vitamin B12 a person needs per day depends on their age.

The intake tables for age and condition as determined by EFSA and the NIH (US Institute of Health) can be seen in the table below:


EFSA (AI/day)*


NIH (CR/day)*

4-6 years


4-8 years old


7-10 years


9-13 years old


11-14 years old
















AI: adequate intake; RQ: recommended amount; RA: recommended amount

Vitamin B12 deficiency

The prevalence of vitamin B12 deficiency according to NHANES (National Health and Nutrition Examination Survey-USA 1999 to 2004) data is 2.9%, increasing to 25% by age, and was generally higher in women (3.3%) than in men (2.4%).

A vitamin B12 level < 200 pg/mL (< 145 pmol/L) indicates vitamin B12 deficiency.3

Why is there a vitamin B12 deficiency?

Vitamin B12 is mainly stored in the liver, and the body stores between 1,000 and 2,000 times the amount usually ingested in a day. This is why it takes several years for symptoms of vitamin B12 deficiency to become apparent.

The causes of vitamin B12 deficiency are:

  1. Inadequate diet: which occurs in vegetarians/vegans, pregnant/lactating women and people with a poor diet.
  2. Inadequate absorption: common in people over 65 years of age, in those with gastrointestinal diseases (sometimes with absence of intrinsic factor), alcoholism, smokers, among others.
  3. Reduced use: due to liver disorders.
  4. Use of some drugs: long-term use of proton pump inhibitors, metformin, continuous exposure to nitric oxide, among others.

What happens if vitamin B12 is lacking?

The first symptoms of an imbalance in the level of vitamin B12 in the body are anaemia, generally known as megaloblastic anaemia, which is closely associated with a reduction in the production of folate and at the same time of DNA, an important material for the production of red blood cells.

Symptoms include fatigue, abdominal pain, gastrointestinal disturbances and weight loss.

Neurological symptoms are shown by decreased perception of position and vibration of the limbs with mild to moderate weakness and hyporeflexia.

In addition, vitamin B12 deficiency can also affect mood, with people showing irritability and mild depression.

Vitamin B12 deficiency in pregnant women

vitamina b12 y embarazadasPregnancy and lactation change the B12 status of the mother in a way that facilitates the transfer of B12 to the fetus and infant, the prevalence being around 10-70% depending on the country.

During pregnancy, extensive physiological and anatomical changes take place in almost all organ systems, with significant consequences on biochemical markers (circulating levels of total B12, holotranscobalamin, MMA and homocysteine), which makes the assessment of micronutrient status more difficult and limits the use of established reference ranges found in non-pregnant women.

In fact, biochemical indicators depend on maternal B12 status and are better in women taking B12 supplements.

The following haemoglobin (Hb) and haematocrit (Hto) concentrations are classified as anaemic:

  • First trimester: haemoglobin < 11 g/dL; Ht < 33%.
  • Second trimester: haemoglobin < 10.5 g/dL; Ht < 32%.
  • Third trimester: haemoglobin < 11 g/dL; Ht < 33%.

Inadequate vitamin B12 intake can also happen in vegetarian/vegan pregnant women, as they may eat little or no food of animal origin.

This condition affects the development of the pregnancy (especially the development of the nervous system in the fetus) and in breast-fed babies.

Breast-fed babies can develop vitamin B12 deficiency between 4-6 months of age because their liver stores are limited and the fast rate of growth increases the demand.

How to know if I am deficient in B12

The tests used to measure the level of vitamin B12 in the body are:

  • Complete blood count and vitamin B12 and folate levels: the blood count detects whether megaloblastic anaemia is present, and the levels of both vitamins to find out which of them is the cause of the anaemia. As mentioned above, the normal level of vitamin B12 should be above 200 pg/ml.
  • Schilling test: sometimes clinical symptoms (such as fatigue, loss of appetite and tingling in the hands and feet) show vitamin B12 deficiency even though blood levels are normal and the haemogram is normal. For this, the amount of methylmalonic acid, which is a compound produced by the metabolism of our body, is evaluated. If it is high, it suggests a vitamin B12 deficiency.

Vegetarian and vegan diets

Dietas vegetarianas y veganasVegetarian and vegan diets are both characterised by the use of moderate or no foods of animal origin.

Vegan diets exclude all food sources of animal origin, while vegetarian diets may include dairy, eggs, bee products and in some cases only eat one type of 'meat', either from fish or chicken.

The daily B12 requirement of 2-3 μg is easily met in those who eat large amounts of animal products or take supplements, but not in vegans who get only 0-0.25 μg daily.3

In both diets there is a possibility of vitamin B12 deficiency due to restricted animal food consumption. This is shown in different studies:

  • In vegans the vitamin B12 level was tested before and after the use of cyanocobalamin. The vitamin B12 level ranged from a deficit of 35 pg/ml to 185 pg/ml.9
  • In Indian adolescent girls on a vegetarian/vegan diet, vitamin B12 intake for 11 months not only increased vitamin B12 levels, but also decreased anaemia by 59% and improved motor function by over 15%.8

Is there plant-derived B12?

Vitamin B12 is produced exclusively by micro-organisms. Animals get this vitamin from grass, where the bacteria responsible for synthesising B12 live, or from B12-enriched feed.1

By contrast, only some algae and mushrooms contain vitamin B12, making plant-based diets inadequate for adequate B12 levels.

Attempts have been made to produce cobalamin  supplements (vitamin B12) from non-animal sources using some algae (e.g. Chlorella) and cyanobacteria such as spirulina (Arthrospira), which is known to contain large amounts of vitamin B12, although unfortunately it is biologically inactive in humans.1

The same applies to fermented foods (such as tempeh), mushrooms, and nutritional yeast, which cannot be considered adequate or practical sources of this vitamin.1

In fact, a 2021 study shows that vegans supplementing with algae, kombucha, yeast and beetroot do not increase vitamin B12 levels, remaining below 35 pg/ml.9

Vitamin B12 foods for vegans

Vitamin B12 is currently provided by controlled biotechnological processes for pharmacological, supplementation and food fortification applications (non-dairy milk, yoghurt, cereals, etc.).

Fortification has been shown in many cases to be insufficient to achieve the recommended daily intakes of cobalamin, so that the risk of deficiency is higher for those who consume plant-based products and do not take B12 supplements.

The food industry is therefore developing plant-based products containing higher amounts of active forms of B12.

Compared to synthetic fortification, fortification with natural vitamin-producing micro-organisms is widely recognised as safer, more natural and more environmentally friendly.1

Some examples1 are:

  • Lupin or lupins: For example, lupin can be used as an alternative substrate for soybeans due to its similar protein content, resulting in "lupin tempeh".
  • Lupin tempeh: In a study by Wolkers-Rooijackers et al. Propionibacterium freudenreichii, a vitamin B12-producing bacterium, was used in co-culture with Rhizopus oryzae to produce B12-enriched lupin tempeh. A significant increase in vitamin B12 content (up to 0.97 μg/100 g) was achieved by fermenting lupin using these two bacteria without affecting other parameters, such as texture and volatile organic compounds.
  • Fenugreek leaf juice (Trigonella foenum graecum): this is another food that can be enriched with B12 (12.5 μg/100 mL) by some lactic fermentations.
  • Sauerkraut: the addition of Propionibacteria to cabbage during sauerkraut production has been shown to lead to higher B12 concentrations (7.2 μg/100 g).

Vitamin B12 supplements

In food supplements it is available in different formats: liquid vitamin B12, vitamin B12 in capsules or vitamin B12 in chewable tablets, among others.

Among the group of molecules that make up vitamin B12, cyanocobalamin is the most widely used form both in the food and pharmaceutical area, which has extensive documentation on efficacy and safety, is highly stable to heat, light and pH, and is also affordable.