What vitamin is necessary for the absorption of B12?

The necessary component for the absorption of vitamin B12 is gastric intrinsic factor, which is produced by the stomach's parietal cells. This glycoprotein binds to vitamin B12 in the stomach, forming a complex that facilitates the absorption of vitamin B12 in the ileum, the final section of the small intestine. Without gastric intrinsic factor, the body cannot effectively absorb vitamin B12, which can lead to deficiencies and associated health problems, such as anemia and neurological issues.

The other choices are related to various roles in nutrition or health but do not directly aid in the absorption of vitamin B12. Vitamin A and vitamin C play significant roles in various metabolic processes and immune function, respectively, while calcium is important for bone health and various physiological functions. However, none of these directly interact with vitamin B12's absorption as gastric intrinsic factor does.