Vitamin B12 is an essential water-soluble vitamin, that is commonly found in a variety of foods, such as fish, shellfish, meat, eggs, and dairy products. It is frequently used in combination with other vitamins in Vitamin B complex formulations [1]. In order to absorb Vitamin B12 from food, the body needs a special transport protein, the so-called Intrinsic Factor (IF). Only 1,5-2 µg of Vitamin B12 can be absorbed per meal or supplementation dosage, because of the limited amount of IF in the body. Additionaly, the body can absorb 1% of supplemented Vitamin B12 through so called diffusion, when it is given in very high dosages. Due to this mechanism, it can be useful to supplement with high doses of Vitamin B12 in order to assure, that sufficient amounts of Vitamin B12 is getting absorbed. Holo-Transcobalamin is the active form of Vitamin B12. If Vitamin B12 blood values are below 400 pg/ml, Holo-Transcobalamin is necessary to unequivocally identify a Vitamin B12 deficiency. [2] [3].

National Nutrition Study

  • 8% of all men do not reach the recommended daily allowance of Vitamin B12.
  • 26% of all women do not reach the recommended daily allowance of Vitamin B12 [9].

Function of Vitamin B12

Vitamin B12 is involved in the synthesis of methionine from homocysteine. Homocysteine is a toxin for the nervous system and the immune system and contributes to  several neurodegenerative and cardiovascular diseases [4] [5] [8].
The vitamin is necessary to activate the function of folic acid, which in turn is also involved in the metabolism of homocysteine [2] [6]
It is involved in the synthesis of DNA; a shortage of Vitamin B12 can lead to an interference of the DNA and RNA synthesis [2] [6] [7].
Vitamin B12 is involved in the so-called erythropoiesis, which is the formation and development of red blood cells. The red blood cells transport oxygen from the lungs to the muscles and organs [2] [6] [7] [8].

Deficiency Symptoms

A deficiency of Vitamin B12 can lead to irritability, light to severe memory disorder and in extreme cases to depression and psychoses [4] [8].
Due to megaloblastic anemia caused by Vitamin B12 deficiency, fatigue, headache, as well as reduced physical performance can appear [4] [7] [8].
A long-term deficiency of Vitamin B12 can lead to degeneration of the spinal cord, which causes serious motor and sensory deficits [4] [8].
Taking vitamin B12 orally in combination with folic acid can reduce serum concentrations of homocysteine [10].

Surplus of Vitamin B12

Toxic effects of a surplus of Vitamin B12 are not known.

[1] Watanabe, F. Vitamin B12 sources and bioavailability. Exp.Biol.Med.(Maywood.) 2007;232(10):1266-1274. (Abstract:

[2] Abels J, Vegter JJM, Woldring MG, et al. The Physiologic Mechanism of Vitamin B12 Absorption. Acta Medica Scandinavica. 1959;165(1):105–113 (

[3] Berlin H, Berlin R, Brante G. Oral Treatrment Of Pernicious Anemia With High Doses Of Vitamin B12 Without Intrinsic Factor. Acta Medica Scandinavica. 1968:184(1):247–258. (

[4] Koula-Jenik, H., Miko M., Kraft M., Schulz R., Leitfaden Ernährungsmedizin. Elsevier,Urban&Fischer Verlag 2013;p.47-49

[5] Alexander Boldyrev, Ekaterina Bryushkova, Anna Mashkina and Elizaveta Vladychenskaya. Current Aging Science (2013) 6: 29.

[6] Christoph Raschka, Stephanie Ruf, Sport und Ernährung: Wissenschaftlich basierte Empfehlungen, Tipps und Ernährungspläne für die Praxis. Georg Thieme Verlag 2015; p.123

[7] Wibusch N, Hofmann P, Förster H, Hörtnagl HLedl-Kurkowski E, Pokan R, Kompendium der Sportmedizin Physiologie, Innere Medizin und Pädiatrie. Springer-Verlag 2016; p. 349

[8] Biesalski HK., Muniz K., Vitamine und Minerale: Indikation, Diagnostik, Therapie. Thieme Verlag 2017; p.103

[9] Max Rubner-Institut, Bundesministerium für Ernährung, Landwirtschaft und
Verbraucherschutz, Hrsg. Nationale Verzehrstudie II. Karlsruhe: MRI; 2008

[10] Dose-dependent effects of folic acid on blood concentrations of homocysteine: a meta-analysis of the randomized trials. Am.J Clin.Nutr 2005;82(4):806-812. (Abstract:

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