The Absorption and Utilization of Vitamin B12

Abstract
The absorption of vitamin B12 in the small intestine from the dietary intake requires an adequate supply of intrinsic factor. In man, the only apparent gastrointestinal source of intrinsic factor is the gastric mucosa. Less than 1 µg./day is the normal requirement of absorbed vitamin B12. The total daily dietary requirement is not known. There is evidence that the biologic rate of decay of this vitamin is relatively slow.