Overview

Vitamin B12, or cobalamin, is required for red-blood-cell formation, neurologic function, and DNA synthesis. Absorption depends on intrinsic factor and the terminal ileum. See Vitamin B12, Vitamin B9, and B-complex vitamins.

Mechanism

Methylcobalamin supports methionine synthase, linking folate recycling with methylation. Adenosylcobalamin supports methylmalonyl-CoA mutase, which converts methylmalonyl-CoA to succinyl-CoA.

Uses

B12 treats deficiency caused by inadequate intake, pernicious anemia, gastric or intestinal disease, or medication-related malabsorption. It may be given orally or by injection depending on cause and severity.

Dosage

Adult dietary reference intake is about 2.4 micrograms/day, with higher values during pregnancy and lactation. Treatment commonly uses high-dose oral or parenteral regimens selected according to laboratory findings, symptoms, and absorption status.

Adverse effects

B12 is generally safe. Rare acneiform eruptions, allergy, or injection-site reactions occur. Neurologic symptoms from deficiency may become irreversible if treatment is delayed.

Claims and evidence

Replacement is clearly beneficial in deficiency. In people with adequate status, B12 does not reliably enhance energy, cognition, or athletic performance.

Research

Research examines biomarkers, oral treatment for malabsorption, pregnancy, neurocognitive outcomes, and links between B12 status and chronic disease.