Terminology
The names vitamin B, vitamin B12, or vitamin B-12, and the alternative name cobalamin, generally refer to all forms of the vitamin. Some medical practitioners have suggested that its use be split into two categories.
- In a broad sense, B12 refers to a group of cobalt-containing vitamer compounds known as cobalamins: these include cyanocobalamin (an artifact formed from using activated charcoal, which always contains trace cyanide, to purify hydroxycobalamin), hydroxocobalamin (another medicinal form, produced by bacteria), and finally, the two naturally occurring cofactor forms of B12 in the human body: 5'-deoxyadenosylcobalamin (adenosylcobalamin—AdoB12), the cofactor of Methylmalonyl Coenzyme A mutase (MUT), and methylcobalamin (MeB12), the cofactor of 5-methyltetrahydrofolate-homocysteine methyltransferase (MTR).
- The term B12 may be properly used to refer to cyanocobalamin, the principal B12 form used for foods and in nutritional supplements. This ordinarily creates no problem, except perhaps in rare cases of eye nerve damage, where the body is only marginally able to use this form due to high cyanide levels in the blood due to cigarette smoking; it thus requires cessation of smoking or B12 given in another form, for the optic symptoms to abate. However, tobacco amblyopia is a rare condition, and it is yet unclear whether it represents a peculiar B12 deficiency that is resistant to treatment with cyanocobalamin.
Finally, so-called pseudovitamin-B12 refers to B12-like analogues that are biologically inactive in humans and yet found to be present alongside B12 in humans, many food sources (including animals), and possibly supplements and fortified foods. In most cyanobacterium, including Spirulina, and some algae, such as dried Asakusa-nori (Porphyra tenera), pseudovitamin-B12 is found to predominate.
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