Stability Vitamin B 12 slowly loses its activity when exposed to light, oxygen and acid or alkali-containing environments, but is stable to heat. Several substituted amide, lactone and lactam analogues of cyanocobalamin compete with binding sites on intrinsic factor and lead to depressed absorption of the vitamin. Nitrous oxide also interferes with cobalamin metabolism. Functions Vitamin B 12 is necessary for the formation of blood corpuscles, nerve sheaths and various proteins. It is also involved in fat and carbohydrate metabolism and is essential for growth.
Reactions involving methylcobalamin include biosynthesis of methionine, methane and acetate.
Deficiency Clinical cobalamin deficiency due to dietary insufficiency is rare. There may be irreversible damage to the nervous system with specific demyelination of the spinal cord. The symptoms of vitamin B 12 deficiency are similar to those of folic acid deficiency, the major difference being that only vitamin B 12 deficiency is associated with spinal cord degeneration. If folic acid is used to treat vitamin B 12 deficiency, the anaemia may be alleviated but the risk of damage to the nervous system remains. It is therefore essential to diagnose the deficiency accurately before starting therapy.