What is required for vitamin B12 absorption?

• A. Intrinsic factor
• B. Vitamin C
• C. Parietal cell acid
• D. Chymotrypsin

Answer: (A)

Vitamin B12 absorption hinges on a specific carrier produced in the stomach: intrinsic factor. B12 must bind to intrinsic factor to form a complex that is recognized by receptors in the terminal ileum and absorbed into the body. Without intrinsic factor, B12 cannot be efficiently absorbed, leading to deficiency even if stomach acids and digestive enzymes are present.

Stomach acid and proteases help free B12 from dietary proteins and from binding proteins, but they do not carry B12 into the bloodstream. Chymotrypsin and other enzymes don’t play a direct role in transport of B12. Vitamin C has no essential role in B12 absorption.