Abstract

The small quantity of vitamin B₁₂ in a normal diet is absorbed by a complex process involving the liberation of the vitamin from food proteins, its combination with a glycoprotein secreted by the gastric mucosa (‘intrinsic factor’), its uptake by the ileal mucosa and its transfer to the blood stream.¹ Vitamin B₁₂ in very large amounts, and probably some of that present in liver and kidney, is absorbed mainly by direct diffusion without the participation of intrinsic factor.