Vitamin B12

Vitamin B12

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The objective of this paper is to give a broad overview not only on the history of the discovery of vitamin B12 but also to synthesize how it is absorbed and causes for its deficiency. Vitamin B12 is unique in its chemical structure which leads to its availability in different forms. However, surgical and infections can interrupt its absorption into the body but this can be cured through the administration of artificial vitamin B12. However, it’s safe to use in any dosage and has no side effects.

Key words: Vitamin B12, chemical structure, artificial, side effects.

















Although they are not an energy source in the human body, vitamins play a significant role in the development of the body, healing, and proper functioning of metabolic and cellular functions. However, all vitamins are not the same and based on how they are available to the body; they are divided into two categories namely; Fat-Soluble Vitamins and Water-Soluble Vitamins. The Fat-Soluble Vitamins require fat to be assimilated and are also stored in the fat to be released when needed. However, most Water-Soluble Vitamins cannot be stored in the body and need to be replenished everyday day through the consumption of foods that are rich in these vitamins except vitamin B12.

Vitamin B12

B Vitamins are Water-Soluble Vitamins that are made up of eight different vitamins among which is Vitamin B12. Also referred to as Cobalamin, this vitamin is required for the proper functioning of the nervous system through the production of myelin and renewal of red blood cells (Scalabrena, 2009). Although the ingestion of liver was directly tied to the recovery of pernicious anaemia patients in 1926, it was not until 1948 that the molecule that was directly tied to the treatment was isolated in crystalline form and named Vitamin B12. Further, in 1956 Dorothy Hodgkin successfully described the chemical structure of Vitamin B12 and received a Nobel Prize in Chemistry in 1964 for her work. Besides, following years of research, Robert Woodwork successfully synthesized Vitamin B12 artificially in 1971 opening the era for safe and complete treatment of most forms of anaemia through oral or intravenous supplementation of this vitamin (Okuda, 1999). Nonetheless, although the deficiency of this vitamin it linked to anaemia, other symptoms usually accompany it especially neuropsychiatric changes. As a result, a deficiency of this vitamin is also a cause for other physiological problems apart from anaemia.

Structure of Vitamin B12

All compounds have a chemical structure that defines its molecules. Although some compounds may be chemically similar with slight differences, vitamin B12 is unique as its chemical makeup is built around a Cobalt metallic ion in the middle of a corrin ring forming a stable bond. However, the cobalt can link to a methyl group to form methylcobalamin which is the form found in human blood and cell cytoplasm. In addition, it can link to a 5- deoxyadenosine at the 5 position resulting in adenosylcobalamin which is a coenzyme in the metabolism of amino acids and fatty acids. Further, it can bond with a cyanide group to result in cyanocobalamin which is usually the synthetic form of vitamin B12 that is produced artificially (Brown, 2005). Consequently, due to its availability in different forms, vitamin B12 is responsible for the proper functioning of the circulatory and nervous systems.

Fig. 1 Vitamin B12 chemical structure (Brown, 2005)




Sources of Vitamin B12

Although vitamin B12 is found in different animal products, advancements have also been made to synthesize it artificially. Thus, among the natural sources of vitamin B12, are meat and dairy products from domestic animals, meats from wild animals, fish and other marine animals among others. Although humans are not capable of synthesizing vitamin B12 in their bodies, most ruminants synthesize it from their foreguts. As such, the only that human beings can obtain the natural form of vitamin B12 is through the consumption of animal products. As such, people who practice strict vegetarianism are in danger of suffering its deficiency (Watanabe et al. 2014). Nonetheless, the vitamin can be produced artificially through fermentation and become available in the form of tablets or injectable solution. Consequently, where symptoms of vitamin B12 are detected, there is a remedy that is safe and secure.

Absorption of Vitamin B12

The absorption of vitamin B12 is essential to ensuring its availability to the body when needed. However, depending on its source, vitamin B12 may be absorbed passively or actively. In passive absorption, the vitamin is absorbed through the buccal, duodenal, and ileal mucosa. However, although this form of absorption is quick, it’s also inefficient. For instance, when supplementation is administered orally, less than 1% of the vitamin is absorbed (Langan and Goodbred, 2017). Thus many countries require that supplementation is done intramuscularly.

Apart from passive absorption, vitamin B12 can also be absorbed actively. This occurs when the vitamin uptake follows the normal physiological process and the supplement is absorbed in the ileum with the mediation of gastric intrinsic factor [IF]. Nonetheless, since the artificial vitamin B12 is not bound by a protein, the absorption through the ileum is also low. However, natural vitamin B12 is also absorbed actively through the interaction of enzymes in the stomach with the protein source and pancreatic trypsin before being transferred to the IF (Hvas and Nexo, 2006). Nonetheless, it is a much more efficient way of absorbing vitamin B12.

Deficiency of Vitamin B12

Although active absorption of vitamin B12 through the physiological mechanisms is an ideal way for the body to acquire the necessary quantities, it may be curtailed leading to deficiencies. For instance, severe stomach inflammation induced by bacterial infections may lead to atrophic gastritis which affects the functioning of small intestines where natural absorption of protein-bound vitamin B12 takes place causing malabsorption.  As a result, a person may suffer from an autoimmune condition known as pernicious anaemia. Further, malabsorption may also be caused by surgical procedures that lead to the removal of parts of the stomach or intestinal tract where vitamin B12 receptors are found. In addition, due to its role in enzyme production, insufficiency in the pancreas may lead to malabsorption. Nonetheless, malabsorption due to stomach and intestinal may be dealt with through the substitution of protein-bound vitamin B12 with the synthetic one since it does not require all the enzymes (Carmel, 2008). However, if the capacity to absorb the vitamin B12 is diminished in the intestinal tract, an intramuscular supplementation is administered to bypass the intestines.

Artificial production

The artificial production of vitamin B12 is through the fermentation of microorganisms that are known to synthesize it. For instance, Pseudomonas dinitrificans and Propionibacterium shrmanii are widely used in the artificial production of vitamin B12. Nonetheless, the process of fermentation begins with the selection of the medium to be used which is either carbon or nitrogen-based. The carbon-based medium includes beet molasses, soybean meal, or corn glucose. However, nitrogen-based are either ammonium phosphate or ammonium hydroxide. After the medium is selected, it is sterilized by autoclaving and inoculated with the selected microorganisms. After the starter culture has been introduced, it is fermented anaerobically for three days followed by four days of aerobic fermentation. Afterwards, the fermented mixture is put in a centrifuge at high speed, and the broth is separated and the thick mass of cells harvested. They are then treated with a weak acid and heat to recover the vitamin B12 (Cheng et al. 2014).


The uptake of vitamin B12 by the body is on demand. As such, the body only absorbs the amount it requires, and the excess is processed and eliminated from the body with urine. Therefore, the administration of excess amounts of vitamin B12 has not been known to have any adverse or side effects on humans. Further, due to the low levels of absorption in oral administration, the likelihood of toxicity is eliminated. In addition, even where supplementation occurs intramuscularly, no side effects have been noted (Carmel, 2008). Thus, vitamin B12 presents no danger of toxicity.


Due to its unique chemical structure and function in the human body, vitamin B12 is irreplaceable. As such, there is no other vitamin that can replace it. However, the lack of or malabsorption of the protein bound vitamin B12 can be replaced by a synthetic version of the same that can be administered orally or intramuscularly.


Vitamin B12 is necessary for the proper functioning of circulatory and nervous systems. Since its discovery, its contribution to the well being of humans has continued to be unraveled. Further, the isolation of its chemical structure led to its artificial production leading to improved management in deficient patients. However, its unique structure enables it to be available in different forms, but it is available naturally in animal meats and products making them the only natural source for human beings. However, synthetic versions are widely available which are made through a fermentation process, but it has no alternative. In addition, it is safe and has no upper limit since the body absorbs only what it requires.





















Brown, K. L. Chemistry and Enzymology of Vitamin B12. Chem. Rev. 2005, 105(6), 2075-2150.

Carmel, R. How I treat cobalamin (Vitamin B12) Deficiency. Blood. 2008,112 (6), 2214-2221.

Cheng, X.; Cheng, W.; Peng, W.F.; Li, K. T. Improved vitamin B12 fermentation process by adding rotenone to regulate the metabolism of Pseudomonas denitrificans. Appl Biochem Biotechnol. 2014, 173 (3), 673-81.

Hvas, A.; Nexo, E. Diagnosis and treatment of vitamin B12 deficiency. Haematologica. 2006, 91, 1506-1512.

Langan, R.C.;Goodbred, A.J. Vitamin B12 Deficiency: Recognition and Management. Am Fam Physician. 2017, 96 (6), 384-389.

Okuda, K. Discovery of vitamin B12 in the liver and its absorption factor in the stomach: A historical review. Journal of Gastroenterology and Hepatology. 1999, 14 (4), 301-308.

Scalabrino, G. The multi-faceted basis of vitamin B12 (cobalamin) neurotrophism in adult central nervous system: Lessons learned from its deficiency. Prog Neurobiol. 2009, 88(3), 203-220.

Watanabe, T.; Yabuta, Y.; Bito, T.; Teng, F. Vitamin B₁₂-containing plant food sources for vegetarians. Nutrients. 2014, 6 (5),1861-73.


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