Which nutrient is absorbed in the ileum?

• A. Vitamin C
• B. Vitamin B12
• C. Iron
• D. Calcium

Answer: (B)

Vitamin B12 absorption hinges on the terminal ileum. B12 must first bind intrinsic factor in the stomach, forming a complex that travels to the ileum, where it is taken up by specialized receptors on enterocytes and endocytosed. This receptor-mediated uptake is why the ileum is the key site for B12 absorption; if the ileum is damaged or removed, B12 cannot be efficiently absorbed, leading to deficiency.

Understanding the other nutrients helps put this in context: Vitamin C is absorbed mainly in the jejunum, not the ileum. Iron absorption occurs predominantly in the duodenum (with some in the proximal jejunum). Calcium is absorbed mainly in the duodenum and proximal jejunum; though some absorption can occur later, the primary site is not the ileum.

So, the nutrient absorbed in the ileum, especially in its B12-Intrinsic Factor form, is vitamin B12.