Vitamin B12
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Introduction
Vitamin B12, or cyanocobalamin, is important for DNA synthesis.
Daily Requirements
There is a 4-5 year store of B12 in your liver.
Sources
Vitamin B12 is found in foods that come from animals:
- meats, especially organ meats
- milk, chesse
- fish
Many cereals are also fortified with B12.
Vitamin B12 is injested and absorbed in the terminal ileum once bound to intrinsic factor, secreted by parietal cells in the stomach.
Biological Roles
required for methoinine and isomerization of methylmalonyl CoA.
It plays an important role in bone marrow and spinal cord metabolism.
Vitamin B12 is required for beta-oxidation of fatty acids with an odd number of carbons, which end up as methylmalonic CoA. Vitamin B12 deficiency leads to urine buildup of methylmalonic acid, leading to metabolic acidosis and developmental disability.
Vitamin B12 is a cofactor for the folate-dependent enzyme methionine synthase. Methionine is an important amino acid.
B12 supplementation of 1000 mcg is effective in reducing number and severity of oral apthous ulcers (canker sores) after 5 months (Volkov et al, 2009).
Deficiency
Vitamin B12 deficiency can occur in Crohn's disease affecting the ileum.
Deficiency of B12 can cause a variety of hematologic, neurologic, and psychiatric conditions, including:
- megaloblastic anemia (pernicious anemia)
- pancytopenia (leukopenia, thrombocytopenia)
- paresthesias
- peripheral neuropathy (especially foot drop)
- combined systems disease (demyelination of dorsal columns and corticospinal tract)
- irritability, personality change
- mild memory impairment, dementia
- depression
- psychosis
- deregulated incorporation of fat in cell membranes, and CNS damage.
Overdose
No known signs of toxicity from foods.
Resources and References
Volkov I et al. 2009. Effectiveness of vitamin B12 in treating recurrent aphthous stomatitis: a randomized, double-blind, placebo-controlled trial. J Am Board Fam Med 22(1):9-16.
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