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 B12.
Vitamin B12 has no observable adverse effects at any level of recorded use.
Sources and Recommended Intake of vitamin B12
All vitamin B12 found in nature is made by microorganisms. The best food sources are those in which this microbial product has moved up the food chain and become relatively concentrated. Such sources include meat (particularly liver), fish, clams, oysters, milk, fermented cheeses, and eggs. Fortified breakfast cereals are also a good source.
Vitamin B12 is virtually absent from fruits, grains, legumes, and vegetables. As such, strict vegetarians are at risk for B12 deficiencies. Note that some vegan foods have been labeled as B12 sources, but the cobalamin-like compounds they contain are inactive in humans.
Human requirements for vitamin B12 are relatively small. The RDA for this nutrient is 2.4mcg/day for adults. Higher levels are suggested for pregnant and lactating women (2.6-2.8mcg/day) and for senior citizens. The average American diet contains 3-7 mcg/day, although this value reflects a high intake of meat.
Despite these figures, it is estimated that a significant percentage of Americans, particularly among vegetarians and the elderly, are B12 deficient.
Which USANA products contain vitamin B12 ?
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