The main cause of cobalamin deficiency is lack of intrinsic factor secretion. Cobalamin malabsorption has also been reported in patients on long-term treatment with certain drugs and in elderly patients with gastric atrophy. There have also been reports of vitamin B 12 deficiency in infants breast-fed by vegetarian mothers. Since 1989, the Food and Nutrition Board of the National Academy of Sciences recommends a daily allowance of 2.0 g for adults, 0.3 g for infants up to 6 months and 0.5 g per day for those between 6 months and 1 year. Supplements Vitamin B 12 injection is available in stable aqueous form as cyanocobalamin or hydroxocobalamin.
Cyanocobalamin is also available as tablet and oral liquid presentations.
Admixture of vitamin B 12 in a zinc tannic acid complex allows slow diffusion from the injection site leading to relatively small losses in urine and high plasma levels over a long period. Vitamin B 12 is also included in a number of multivitamin preparations, marketed as nutritional supplements for anaemia. Therapeutic use Patients with lack of intrinsic factor secretion require lifetime vitamin B 12 therapy. When used alone, oral doses of at least 150 g per day are necessary, although single weekly oral doses of 1000 m g have proved satisfactory in some cases. Combinations of vitamin B 12 and intrinsic factor may be given, but as a variable number of patients become refractory to intrinsic factor after prolonged treatment, parenteral therapy with cyanocobalamin or hydroxocobalamin is preferred.