Vitamin B12 (Methylcobalamin)

• Methylation & One-Carbon Metabolism: MeCbl enables methionine synthase to regenerate methionine from homocysteine, sustaining S-adenosylmethionine (SAM) for methylation of DNA, RNA, neurotransmitters, and phospholipids.
• DNA Synthesis & Repair: By linking folate and methionine cycles, MeCbl supports nucleotide synthesis and cell division.
• Neurologic Function: Adequate methylation helps maintain myelin integrity and neurotransmitter balance.
• Hematopoiesis: Proper B12/folate status supports erythroblast maturation; deficiency can cause macrocytosis and anemia.

Causes of malabsorption include pernicious anemia (autoimmune loss of IF), gastric surgery, achlorhydria, pancreatic insufficiency, and ileal disease.

• Risk factors: vegan/very low-animal-product diets, elderly, pernicious anemia, gastric/ileal surgery, metformin use, long-term acid suppression, malabsorption disorders.
• Hematologic: macrocytosis, megaloblastic anemia, hypersegmented neutrophils.
• Neurologic: paresthesia, gait disturbance, cognitive/mood changes; prolonged deficiency may cause irreversible damage.

• Serum B12: screening marker but can be misleading alone.
• Methylmalonic Acid (MMA): rises when AdoCbl-dependent mutase is limited; sensitive for cellular B12 deficiency.
• Homocysteine: elevated with impaired MeCbl-dependent methionine synthase (also influenced by folate/B6).
• Holo-Transcobalamin (holo-TC): the biologically available B12 fraction; often correlates with tissue delivery.
• CBC with indices: macrocytosis (↑MCV) in megaloblastic states.

• Folate linkage: Treating folate deficiency may normalize anemia while masking neurologic B12 deficiency—evaluate both.
• Medications: Metformin and long-term H2 blockers/PPIs are associated with lower B12 status in some populations.
• Nitrous oxide exposure: Oxidizes the B12 cobalt center and inactivates methionine synthase—can precipitate acute neurologic issues in the deficient.

• Dietary sources: animal products (meat, fish, dairy, eggs) and fortified foods.
• Supplemental forms: methylcobalamin (MeCbl), adenosylcobalamin (AdoCbl), cyanocobalamin (CNCbl), hydroxocobalamin (OHCbl).
• Stability: cobalamins are light-sensitive; protect from light/heat; follow manufacturer storage guidance for research materials.

Recommended Dosage:  1ml once per week

Molecular Formula: C₆₃H₉₁CoN₁₃O₁₄P

Molecular Weight: \approx 1344.4 g mol^-1

Notes: Methylcobalamin is a cobalt-corrin macrocycle with an upper axial methyl ligand.

Is methylcobalamin the same as “Vitamin B12”?

It’s one of the active forms of Vitamin B12. The other active coenzyme is adenosylcobalamin; cyanocobalamin/hydroxocobalamin are common supplemental/parent forms that convert to active forms in vivo.

Which coenzyme form runs methylmalonyl-CoA mutase?

Adenosylcobalamin (AdoCbl), not methylcobalamin.

Which lab markers are most informative?

A panel including MMA, homocysteine, holo-transcobalamin, serum B12, and CBC indices provides better context than a single marker.

PubMed

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