Overview

Vitamin B12, or cobalamin, is required for red-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, while adenosylcobalamin supports methylmalonyl-CoA mutase. Deficiency elevates methylmalonic acid and can injure nerves even without anemia.

Uses

B12 prevents and treats deficiency caused by vegan diets, pernicious anemia, gastric or intestinal disease, bariatric surgery, or medicines that impair absorption. Oral, sublingual, and injectable forms may be selected according to cause and severity.

Dosage

Adult dietary reference intake is about 2.4 micrograms/day; pregnancy and lactation require more. Treatment doses are often much higher and may be oral or injectable. Clinicians use blood count, B12, methylmalonic acid, homocysteine, and symptoms to guide therapy.

Adverse effects

B12 is generally safe. Acneiform eruptions and rare hypersensitivity reactions have been reported. Treat suspected neurologic deficiency promptly rather than relying on self-testing.

Claims and evidence

Replacing B12 deficiency is strongly evidence-based. In people with adequate status, supplements have not been shown to provide a general energy, memory, or anti-aging effect.

Research

Research examines biomarkers, cognition, neuropathy, pregnancy, microbiome interactions, and treatment strategies for malabsorption and inherited cobalamin disorders.