Limits of Absorption of Orally Administered Vitamin B12: Effect of Intrinsic Factor Sources.

Abstract

When the dose of vit B12 was increased from 0.5 ug to 2.0 ug% an increased amount was absorbed, and an additional increase occurred when the dose was increased to 5.0 ug, but above 5.0 ug, no increased increment of absorption occurred. Giving intrinsic factor to normal individuals did not increase the absorption. In fact there appeared to be an inhibition in 3 out of 4 normal subjects when intrinsic factor was given with a dose of 5.0 ug of vit B12. In 2 patients who had a total gastrectomy and who excreted 100% of the administered test dose, giving increasing amounts of intrinsic factor restored the observation of radiovitamin normal. It was found that in 4 individuals, who absorbed poorly, there was considerably greater absorption of radiovitamin B12 when it was given with a meal than when it was given between meals. (In 3 individuals with good absorption no change occurred). Apparently, food stimulated the secretion of intrinsic factor. The upper level of vit. B12 absorption appeared to be about 1.6 ug. This level cannot be increased by increasing the dose of vitamin, by giving it with a test meal, or in conjunction with intrinsic factor sources.