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vitamin B12A water-soluble vitamin of animal origin required for DNA synthesis. It is a glycoprotein produced and secreted by the gastric parietal cells, and is absorbed from the GI tract bound to intrinsic factor; the body stores up to one years’ worth of vitamin B12 in the liver, kidneys and heart. Rapid cell turnover (e.g., growth spurts in children, malignancy) require increased amounts of vitamin B12. Vegans, who ingest no protein of animal origin, are at risk for vitamin B12 deficiency.
Chronic myeloid leukaemia, chronic obstructive pulmonary disease, congestive heart failure, liver disease, obesity, polycythemia vera, renal failure.
Atrophic gastritis, drugs (antibiotics, anticonvulsants, antimalarials, antituberculous agents, chemotherapy, contraceptives, diuretics, oral hypoglycemics, sedatives), inflammatory bowel disease (e.g., Crohn’s disease, ulcerative colitis), intrinsic factor deficiency (causing megaloblastic anaemia), malabsorption, malnutrition, parasites (e.g., Diphyllobotrium latum), veganism.