فيتامين ب 12 vitamin

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 it is absorbed in the intestine.

The complex formed by this vitamin 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

What is the use of vitamin B12?

It 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.

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

It 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:

  • Inadequate diet: which occurs in vegetarians/vegans, pregnant/lactating women and people with a poor diet.
  • 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.
  • Reduced use: due to liver disorders.
  • 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 this vitamin 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, its deficiency can also affect mood, with people showing irritability and mild depression.

Vitamin B12 deficiency in pregnant women

Pregnancy 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, 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 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 this vitamin 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

  • 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 this vitamin 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 deficiency.

Is there plant-derived B12?

It 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.

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 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.

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

Food supplements

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

Among the group of molecules that make up this vitamin, 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.

 References:

  • Alcorta, A. et al. Foods for Plant-Based Diets: Challenges and Innovations. Foods 2021, 10, 293 (2021).
  • Brito, B. M. et al. sources in non-animal foods: a systematic review. Crit Rev Food Sci Nutr. 2022 Mar 28;1-15.
  • Green, R. et al. Nature Reviews Disease Primers 3(1):17040 (2017).
  • Langman, M. Safe Upper Levels for Vitamins and Minerals. Expert Group on Vitamins and Minerals, May 2003. Published by Food Standards Agency. ISBN 1-904026-11-7.
  • Pellinen, T. et al. Replacing dietary animal-source proteins with plant-source proteins changes dietary intake. And status of vitamins and minerals in healthy adults: a 12-week randomized controlled trial. Eur J Nutr. 2022; 61(3): 1391–1404.
  • Salguero Hinojosa, A. Veganismo, vegetarianismo e infancia. Una revisión sobre la realidad de una combinación muy polémica. Trabajo de Fin de Grado de Enfermería. Universidad Autónoma de Madrid, 2021.
  • Tolerable Upper Intake Levels for Vitamins and Minerals. Scientific Committee on Food Scientific Panel on Dietetic Products, Nutrition and Allergies, February 2006. European Food Safety Authority. ISBN: 92-9199-014-0.