Limits of Absorption of Orally Administered Vitamin B 12

Summary

The results show the extreme limitation of vit. B₁₂ absorption from the gastrointestinal tract of individuals with normal gastric function. Within the dose range used, an upper level of absorption appears to have been reached which averages 1.6 μg vit. B₁₂. This level is not increased by giving the vitamin with a test meal or in conjunction with intrinsic factor sources. In patients with a total gastrectomy, a graded response to intrinsic factor is obtained using 0.5 μg vit. B₁₂ but at a 5 μg level, increasing the amount of intrinsic factor does not increase B₁₂ absorption beyond levels obtained in normal subjects.