Handbook of vitamin B12

The term Vitamin B12 is used as a generic descriptor for the cobalamins; cobalt containing compound possessing the corrin ring having the biological activity of vitamin. The active coenzyme forms of Vitamin B12 are methylcobalamine and deoxyadenosylcobalamin. Dietary sources of vitamin B12 are of animal origin and include meat, eggs, milk, dairy products, fish and poultry. Vitamin B12 is absent in plant foods and humans obtain small amount of Vitamin B12 from their intestinal flora. Vitamin B12 plays a crucial role in DNA synthesis, nucleoprotein, erythropoiesis, myelin synthesis, normal growth and cell reproduction and one carbon metabolism. Vitamin B12 deficiency may arise due to decreased dietary intake. Vitamin B12 helps in isomerization of methylmalonyl-CoA to succinyl-CoA by methylmalonyl-CoA mutase and also helps in conversion of homocysteine to methionine by methionine synthase. Dietary deficiency is seen in strict vegetarians, since vitamin found only in foods of animal origin or in microorganism. Deficiency of Vitamin B12 causes pernicious anemia, megaloblastic anemia, methylmalonic aciduria, Neuropathy and folate trap.