where is b12 absorbed in the gi tract
Intrinsic factor Intrinsic factor (IF), also known as gastric intrinsic factor (GIF), is a glycoprotein produced by the parietal cells of the stomach. It is necessary for the absorption of vitamin B12 later on in the ileum of the small intestine.[5] In humans, the gastric intrinsic factor protein is encoded by the GIF gene.[6]:989