Vitamin B12

Methylcobalamin normalized/increased B12 status and improved several prespecified neuropathy-related measures, including vibration-perception threshold, pain score, quality of life, sural nerve conduction velocity, sural nerve action-potential amplitude, and foot electrochemical skin conductance. Cardiovascular autonomic reflex tests and the MNSI examination component did not significantly improve. Relevant to a low-B12, metformin-treated diabetic-neuropathy population -- should NOT be generalized to cognitive enhancement, energy, or neuropathy in B12-replete healthy people.

Low B12 was more common in the metformin group at 5 years, and combined low/borderline-low B12 was more common with metformin at both 5 and 13 years. Each year of metformin use was associated with higher odds of B12 deficiency. Supports metformin exposure as a clinically relevant B12-deficiency risk factor; does not show that methylcobalamin has benefits beyond correcting/preventing deficiency.

Methionine synthase transfers the methyl group from bound methylcobalamin to homocysteine, producing methionine and cob(I)alamin; the cobalamin cofactor is then remethylated by methyltetrahydrofolate. The paper experimentally dissects enzyme regions involved in homocysteine, methyltetrahydrofolate, cobalamin, and adenosylmethionine handling. Strong direct mechanistic support for the methylcobalamin -> methionine synthase -> homocysteine-to-methionine pathway.

The label identifies the active drug as cyanocobalamin, a form distinct from methylcobalamin, and indicates it for vitamin B12 deficiencies caused by malabsorption, including pernicious anemia and several gastrointestinal causes. Describes B12 transport, hepatic storage, intrinsic-factor-dependent GI absorption, and neurologic consequences of deficiency. Strong evidence that FDA-regulated B12 drug products exist -- NOT evidence that the ERP methylcobalamin product is FDA approved.

CYANOKIT contains hydroxocobalamin and is FDA-indicated for treatment of known or suspected cyanide poisoning. Sharply illustrates why regulatory status must be attached to the exact cobalamin form and product: an FDA-approved hydroxocobalamin indication cannot be used to imply regulatory approval of methylcobalamin or generic "Vitamin B12."

Vitamin B12 is a water-soluble cobalamin required for nervous-system function, red blood-cell formation, and DNA synthesis. Methylcobalamin and 5-deoxyadenosylcobalamin are metabolically active forms; B12 is a cofactor for methionine synthase and methylmalonyl-CoA mutase, which use different active cobalamin forms. Food B12 is released from food proteins, binds haptocorrin, transfers to intrinsic factor, and is absorbed in the distal ileum. Documents megaloblastic anemia and neurological manifestations of deficiency, pernicious anemia/malabsorption risk, vegetarian/vegan risk, GI-surgery risk, and medication-associated risk. States that B12 supplementation does not appear to improve athletic performance or endurance in people with sufficient B12 status.

B12 absorption requires a coordinated pathway involving haptocorrin, gastric intrinsic factor, pancreatic digestion, distal-ileal uptake through the cubilin/amnionless receptor complex, and transcobalamin-mediated transport. Identifies inadequate dietary intake, pernicious anemia/intrinsic-factor deficiency, gastrectomy/bariatric surgery, ileal disease and other GI disorders as causes of deficiency or malabsorption.

Vitamin B12 deficiency is a leading cause of megaloblastic anemia and can produce neurologic and neurocognitive manifestations. Severe deficiency commonly reflects failure of gastric or ileal absorption, classically pernicious anemia; milder deficiency may arise from food-cobalamin malabsorption or dietary inadequacy. Clinical manifestations are variable, and diagnosis should not rely on a single laboratory test.

Methylcobalamin and adenosylcobalamin are the coenzyme forms for methionine synthase and methylmalonyl-CoA mutase, respectively. Cyanocobalamin and hydroxocobalamin are common supplementation/treatment forms that undergo intracellular processing into active coenzymes. Does not support assuming methylcobalamin is generally superior to cyano- or hydroxocobalamin for prevention/treatment of ordinary cobalamin deficiency.