Vitamin B12

Vitamin B12, or cobalamin, is an essential water-soluble vitamin needed for DNA synthesis, red blood cell formation, and normal nervous system function.

Intrinsic factor: A stomach-produced protein that binds vitamin B12 and enables its absorption in the small intestine. B12 must bind this protein to be absorbed efficiently in the ileum.
Megaloblastic anemia: An anemia marked by abnormally large, immature red blood cell precursors caused by impaired DNA synthesis. B12 deficiency can impair DNA synthesis in developing blood cells and produce this pattern.
Vitamin B12 deficiency: A state in which vitamin B12 supply or activity is insufficient for normal physiological function. It is the main clinical condition detected and treated through B12 testing and replacement.
Cobalamin: A family of cobalt-containing compounds with vitamin B12 activity. Vitamin B12 is the common name for this group of related compounds.
Vitamin B12 biomarkers: Laboratory measures used to assess vitamin B12 status, including total B12, holotranscobalamin, methylmalonic acid, and homocysteine. No single marker captures every aspect of B12 availability and function.
Terminal ileum: The final section of the small intestine, where bile salts and vitamin B12 bound to intrinsic factor are absorbed. This is the principal site where the intrinsic factor–B12 complex enters the body.
Pernicious anemia: An autoimmune condition in which loss of intrinsic factor or stomach cells prevents adequate vitamin B12 absorption. It is a major cause of severe B12 deficiency and may cause neurological injury.
Serum vitamin B12 test: A blood test measuring circulating vitamin B12 concentration. It is commonly used to investigate suspected deficiency, though borderline results need interpretation.
Cobalt: A chemical element with symbol Co and atomic number 27. A cobalt ion sits at the center of every cobalamin molecule.
Vitamin B12 and cognition: The relationship between vitamin B12 status and cognitive performance or decline. Low B12 can accompany cognitive symptoms, while benefits of supplementation without deficiency remain uncertain.

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