Which vitamin is primarily absorbed in the terminal ileum?

• A. Vitamin B12
• B. Vitamin C
• C. Vitamin D
• D. Thiamine

Answer: (A)

The main concept here is that vitamin B12 absorption depends on a specialized process that occurs in the terminal ileum. B12 from the diet first binds intrinsic factor produced by the stomach; this IF–B12 complex travels to the terminal ileum, where it binds to receptors on ileal enterocytes (cubilin/amnionless) and is absorbed. Once inside the cells, B12 is handed off to transport proteins to reach circulation. This site-specific, receptor-mediated uptake is why the terminal ileum is essential for B12 absorption.

Other vitamins don’t share this exact requirement or site. Vitamin C is absorbed mainly in the jejunum through specific transporters, not in the terminal ileum. Vitamin D is fat-soluble and absorbed along the small intestine with lipids, not confined to the terminal ileum. Thiamine is absorbed primarily in the duodenum and jejunum via distinct transport systems.