Which vitamin requires intrinsic factor for absorption?

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

Answer: (C)

Vitamin B12 requires intrinsic factor for absorption because intrinsic factor is a glycoprotein produced by the parietal cells of the stomach. It binds to vitamin B12 in the gastrointestinal tract, which is necessary for the vitamin's transport and absorption in the ileum, the last part of the small intestine. Without intrinsic factor, vitamin B12 cannot be efficiently absorbed, leading to deficiencies that can cause anemia and neurological issues, often seen in conditions such as pernicious anemia.

The other vitamins listed do not require intrinsic factor for their absorption processes. Vitamin C is absorbed in the intestines through different mechanisms, primarily involving sodium-dependent transporters. Vitamin D is absorbed from dietary sources or synthesized in the skin and does not depend on intrinsic factor. Similarly, vitamin A is absorbed in the intestine through a different set of transport proteins and does not rely on intrinsic factor for its absorption. Therefore, the necessity of intrinsic factor in the absorption of vitamin B12 makes it the correct answer for this question.