Vitamin B-12 is a water-soluble vitamin in a family of compounds called cobalamins, which contain the mineral cobalt, according to the National Institutes of Health's Office of Dietary Supplements. The Linus Pauling Institute at Oregon State University notes that vitamin B-12 is the largest and has the most complex chemical structure of any vitamin. A daily intake of 2 mcg of vitamin B-12 is recommended for adults. Shellfish, finfish, meat and dairy products are sources of vitamin B-12.
Methylcobalamin
Methylcobalamin and 5-deoxyadenosylcobalamin are the forms of vitamin B-12 that are active in human metabolism. Methylcobalamin is involved in chemical reactions in the body that produce DNA, hormones, proteins and fats and help prevent cancer. A deficiency of methylcobalamin can impair DNA production and cause pernicious anemia, a disease characterized by insufficient hemoglobin in red blood cells. Hemoglobin is a protein carried by red cells that gets oxygen from the lungs and delivers it to other parts of the body. Methylcobalamin deficiency can also increase the risk of cardiovascular disease.
5-Deoxyadenosylcobalamin
5-Deoxyadenosylcobalamin is involved in chemical reactions in the body that produce energy from fats and proteins and synthesize hemoglobin. Deficiencies of vitamin B-12 can be diagnosed by measuring urine levels of a byproduct of vitamin B-12 called methylmalonic acid. High levels of methylmalonic acid in the urine indicate a vitamin B-12 deficiency.
Cyanocobalamin
Cyanocobalamin is the form of vitamin B-12 used in most nutritional supplements. In the body, cyanocobalamin is converted to methylcobalamin and 5-deoxyadenosyl. Since vitamin B-12 is found in fish, shellfish, meat and poultry, and to lesser extent in dairy but not in plant foods, vegetarians are especially vulnerable to vitamin B-12 deficiencies and need supplements containing either cyanocobalamin or methylcobalamin to meet the daily requirements. It is best to consult a physician to determine the body's levels of vitamin B-12 and the type and amount of supplements needed.
Cyanocobalamin is available in over-the-counter pills, either alone or part of a multivitamin or B-complex product, or as an injectable prescription drug, according to Drugs.com. Vitamin B-12 does not have any known toxicity or adverse effects when taken in doses as high as 1000mcg or 1mg by mouth or intramuscular injection; when taken by mouth only a small percentage of the vitamin is absorbed into the body. (see reference 2) Injection of cyanocobalamin is indicated for vitamin B-12 deficiencies from malabsorption associated with pernicious anemia, overgrowth of bacteria or fish tapeworm in the small intestine, gastrointestinal dysfunction, stomach or intestinal cancer or deficiency of folic acid. (see reference 6) These conditions can be diagnosed by a physician prior to prescription for vitamin B-12 injection.
References
- National Institutes of Health's Office of Dietary Supplements: Vitamin B-12
- Oregon State University's Linus Pauling Institute: Vitamin B-12
- Institute of Medicine's Food and Nutrition Board: Recommended Intakes for Individuals
- VeganHealth.org: Coenzyme Functions
- U.S. Department of Agriculture: National Nutrient Database
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