We have already written extensively on the topic of Vitamin B12. Vitamin B12 is one of the most important biologically active substances required by the human body.

The daily intake of vitamin B12 is roughly 3 µg. (1) It seems like that could be easily achieved by supplementation or having a moderate amount of meat, nuts and eggs. However, the reality is different. 

Not all vitamin B12 in the body can be used for its purpose. Not all vitamin B12 is ‘bioavailable’. Bioavailability is defined as “the efficiency with which a dietary component is used systematically through normal body functions” and expressed as a percentage of intake. (2)

Currently, the bioavailability of vitamin B12 is generally assumed to be 40 or 50% for healthy adults with normal gastrointestinal functioning. (3) This assumption is based on the absorption of labelled vitamin B12 from a few food products, including mutton and chicken meat, rainbow trout, eggs or fortified foods. (4)

The reasons for the loss of bioavailable vitamin B12 are natural disintegration, gastro-intestinal disorders, stress and age. In other words, if you suffer from even occasional heartburn, very little vitamin B12 is being absorbed in your body.

The signs of Vitamin B12 deficiency are:

  • Pale or yellowish skin
  • Constant fatigue
  • Pins and needles felt around the body
  • Poor mobility – a person deficient in B12 becomes slow and clumsy
  • Mouth ulcers 
  • Dizziness and shortness of breath
  • Blurred and disturbed vision
  • Mood changes

It is estimated that 40% of people are Vitamin B12 deficient.

Testing for Active vitamin B12 is a good way of determining a true vitamin B12 deficiency. Once identified, the Vitamin B12 deficiency is easily rectified by parenteral supplementation.



  1. Doets EL, Cavelaars AE, Dhonukshe-Rutten RA, van ‘t Veer P, de Groot LC: Explaining the variability in recommended intakes of folate, vitamin B12, iron and zinc for adults and elderly people. Public Health Nutr 2012;15:906-915.
  2. Aggett PJ: Population reference intakes and micronutrient bioavailability: a European perspective. Am J Clin Nutr 2010;91:1433S-1437S.
  3. Martin A: The ‘Apports nutritionnels conseillés’ (ANC) for the French population, ed 3. CNRS/CNERNA/AFSSA. Paris, Tec & Doc Lavoisier, 2001.
  4. Doscherholmen A, McMahon J, Economon P: Vitamin B12 absorption from fish. Proc Soc Exp Biol Med 1981;167:480-484.