Vitamin B12 is essential for normal energy metabolism of carbohydrates, fat and protein. As a cofactor for
methylmalonyl-CoA mutase enzymes, vitamin B12 helps convert odd chain fatty acids and branched chain
amino acids into succinyl-CoA, a common citric acid cycle intermediate. Vitamin B12 is also required for
nucleic acid (DNA) synthesis, methionine synthesis from cysteine, and normal myelin synthesis in the nervous
system. Along with vitamin B6 and folic acid, adequate levels of vitamin B12 are required to maintain normal
plasma homocysteine levels. Elevated plasma homocysteine may be an independent risk factor for
developing heart conditions.†
There are two distinct mechanisms for intestinal vitamin B12 absorption; receptor-mediated absorption and
passive diffusion. In the first, vitamin B12 attaches to a salivary “R-binder” protein which transports it into the
small intestine, where vitamin B12 is released. The vitamin then binds to “Intrinsic Factor” (IF), a glycoprotein
normally produced by the gastric parietal cells. This vitamin B12-IF complex is carried down to the ileum, where
it binds to mucosal receptors. Finally, the complex is absorbed and bound to serum vitamin B12-binding
proteins. The second absorption mechanism, passive diffusion, does not require any carriers, such as B-binder
or IF. The elderly and strict vegetarians are often at risk for vitamin B12 deficiency, either due to low dietary
intake or impaired absorption.
The receptor-mediated absorption pathway is subject to numerous genetic and pathologic defects which can
severely impair normal vitamin B12 absorption. These defects include hereditary absence of IF production,
gastric atrophy, gastrectomy, and small intestinal disorders affecting the ileum. Affected individuals depend
almost exclusively on the passive diffusion pathway or by dissolving tablets in the mouth.
Vitamin B-12 tablets are indicated for individuals that desire higher intakes of the nutrient B-12 in a dissolvable
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