Which vitamin requires intrinsic factor for intestinal absorption?

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

Answer: (A)

Vitamin B12 absorption hinges on intrinsic factor, a glycoprotein made by stomach parietal cells. It binds B12 in the gut to form a complex that travels to the terminal ileum, where specialized receptors take up the complex and allow B12 to enter the body. Without intrinsic factor, B12 cannot be efficiently absorbed, leading to deficiency and conditions like pernicious anemia. Other vitamins listed don’t rely on intrinsic factor for uptake: vitamins A and D are fat-soluble and depend on fat digestion and bile; vitamin C is water-soluble and absorbed by distinct transporters without IF involvement. (Note that a small amount of B12 can be absorbed passively at very high doses, but this is not enough for normal nutrition.)