Vitamin B12

Vitamin B12 is a.k.a cobalamine is a water-soluble vitamin involved in CNS functioning and formation of red blood cells. Vitamin B12 deficiency is usually associated with megaloblastic macrocytic anemia due to defective DNA synthesis, and may ultimately lead to neurologic damage. Intrinsic factor (IF), produced by the stomach, is crucial for vitamin B12 absorption, and lack of IF can lead to B12 deficiency and pernicious anemia. Vitamin B12 deficiency results in elevated serum levels of homocysteine and methylmalonic acid. First, vitamin B12 is use in the generation of tetrahydrofolate, which is used in the conversion of homocysteine to methionine. Second, B12 is a cofactor in the conversion of methylmalonyl-CoA to succinyl-CoA in the Kreb cycle. Therefore, laboratory tests for homocysteine or methylmalonic acid levels can be used as indicators for B12 deficiency as well in conjunction with B12 levels.

Take home points: B12 deficiency may show both hyperhomocyteinemia and an elevated MMA (Methyl Malonic Acid) while Folate deficiency may show hyperhomocyteinemia but no elevation in MMA.