Vitamin B-12 is one of the largest and most complex vitamins. Part of this complexity arises from the fact that B-12 is the only vitamin that contains a cobalt metal ion, which is the reason why the term "cobalamin" is also used to refer to this vitamin. Several different synthetic and naturally occurring forms of vitamin B-12 exist, which have slightly different properties.
Cobalamin and Cyanocobalamin
The term cobalamin is the most general term for vitamin B-12. Cyanocobalamin was the first synthetic form of cobalamin, created in a laboratory. Most vitamin B-12 supplements contain cyanocobalamin. Supplements containing cyanocobalamin are available in several forms including an injectable liquid, a nasal gel or a pill that can be taken orally. You can purchase cyanocobalamin by itself, in multivitamins or in B-complex vitamins.
Hydroxocobalamin
Hydroxocobalamin is another synthetic form of vitamin B-12. The process to create hydroxocobalamin was discovered later than the process to create cyanocobalamin; consequently, hydroxocobalamin is not used as commonly as cyanocobalamin. Both forms have very similar properties, although they may cause slightly different side effects in different people.
Methylcobalamin
The body converts vitamin B-12, given as either cyanocobalamin or hydroxocobalamin, into other active forms of cobalamin to fulfill different functions within the body. One example is methylcobalamin, which is a slightly modified form of cobalamin that interacts with an enzyme called methionine synthase, a critical enzyme involved in DNA synthesis.
Adenosylcobalamin
Another active form of vitamin B-12 is adenosylcobalamin. This form of cobalamin interacts with a different enzyme called methylmalonyl CoA mutase, a metabolic enzyme involved in breaking down fatty acids in the body. The body converts cobalamin into its different forms, depending on the current needs of the body. Bacteria living in the intestines or liver may create additional forms of cobalamin, although the functions, if any, of these forms are not well understood.
References
- "Clinical Biochemistry"; Significance of Elevated Cobalamin (Vitamin B12) Levels in Blood; A.A.M. Ermens et al.; November 2003
- Linus Pauling Institute at Oregon State University: Vitamin B12
- Vitamins-Supplements.org: Vitamin B12 (Cyanocobalamin, Cobalamin)
- Office of Dietary Supplements of the National Institutes of Health: Vitamin B12
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