Achlorhydria and crystalline B12 absorption.

• A. Crystalline B12 absorption is enhanced by absence of gastric acid.
• B. Crystalline B12 absorption is not affected by gastric acid.
• C. Crystalline B12 absorption is completely blocked by achlorhydria.
• D. Crystalline B12 requires higher acidity to be absorbed.

Answer: (B)

Crystalline B12 is absorbed independently of gastric acid because it is not bound to dietary protein and can be taken up by passive diffusion in the ileum, even without intrinsic factor. In achlorhydria, the release of B12 from protein in foods is impaired, but this does not affect the crystalline form, which can still be absorbed in small amounts without gastric acid. The amount absorbed via this passive route is limited (about 1%), but the presence or absence of gastric acid does not significantly change this process. The other ideas imply that acid status changes the absorption of crystalline B12 or that it’s blocked or needs more acidity, which isn’t correct for the crystalline form.