Vitamin B12 (cobalamin) is a water-soluble vitamin essential for DNA synthesis, red blood cell formation, and neurological function.
Biochemical role
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Acts as a cofactor for methionine synthase (converts homocysteine to methionine) and methylmalonyl-CoA mutase (converts methylmalonyl-CoA to succinyl-CoA).
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Supports synthesis of myelin and nucleic acids.
Sources
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Found only in animal-derived foods: meat, liver, fish, eggs, milk, cheese.
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Vegan diets require fortified foods or supplements.
Absorption
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Requires intrinsic factor secreted by stomach parietal cells.
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Absorbed in the terminal ileum; deficiency can arise from pernicious anemia, gastric surgery, or intestinal disorders.
Deficiency symptoms
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Megaloblastic anemia (due to impaired DNA synthesis).
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Neurological issues: numbness, tingling, memory loss, confusion.
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Elevated homocysteine and methylmalonic acid levels.
Supplementation
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Cyanocobalamin and methylcobalamin are common forms.
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Oral doses: 250–1000 µg daily for mild deficiency; intramuscular injections for severe or absorption-related cases.
Toxicity
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No known toxicity; excess is excreted in urine.
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