Vitamin B₁₂ is a water-soluble B vitamin essential for human health and well-being. Its chemistry - the most complex of all the vitamins - is unique in two respects. It is the only vitamin that contains a mineral component, and it is also one of the few essential substances in the body that contains the mineral cobalt. Vitamin B₁₂ is frequently referred to as cyanocobalamin, but technically this is a misnomer. Cyanocobalamin is the principal pharmaceutical or supplemental form of vitamin B₁₂ (used because it is chemically stable). In the human body, however, cyanocobalamin must be converted into one of two related cobalamin molecules before becoming metabolically active.

Vitamin B₁₂ is a coenzyme, meaning that its function is closely associated with (and essential for) the activity of one or more enzymes. In humans, vitamin B₁₂ binds to an enzyme responsible for part of the cyclic metabolism of folic acid, another B-vitamin required for amino acid metabolism, the synthesis of nucleic acids, red blood cell formation, and myelin synthesis and maintenance. A shortage of vitamin B₁₂ results in an interruption of folic acid regeneration and the development of disorders associated with folic acid deficiency. As such, vitamin B₁₂ deficiencies are often mistaken for folic acid deficiencies both in laboratory tests and in analysis of clinical symptoms.

Absorption of vitamin B₁₂ is a multi-stage process, and defects in any one of the enzyme systems required for release, transport, and absorption of B₁₂ can result in a deficiency. Deficiencies also result from inadequate B₁₂ in the diet. Clinical symptoms of vitamin B₁₂ deficiency include pernicious anemia, numbness and tingling in the hands and feet, poor balance, poor coordination, and a loss of mental acuity. Vitamin B₁₂ deficiencies are often difficult to diagnose.

Vitamin B₁₂ works alongside folic acid and vitamin B₆ in the maintenance of homocysteine levels, an independent risk factor of cardiovascular disease.

All vitamin B₁₂ found in nature is made by microorganisms. Therefore, the usual dietary sources include meat and meat products, and to a lesser extent milk and milk products. Strict vegetarians (including vegans) can develop a deficiency since they receive no vitamin B₁₂ from their diet unless their food is contaminated by microorganisms. Vitamin supplementation is the only sure way for vegans to get sufficient vitamin B_12.

Vitamin B₁₂ has no observable adverse effects at any level of recorded use.

• Vitamin B12 - U.S. National Library of Medicine
• Vitamin B12 - Mayo Clinic
• Vitamin B12 - Linus Pauling Institute
• Vitamin B12 - Wikipedia
• www.b12vitamin.com