Which vitamin is crucial for normal blood clotting?

Vitamin K is essential for normal blood clotting because it plays a critical role in the synthesis of certain proteins known as clotting factors. These proteins are necessary for the blood coagulation process, which prevents excessive bleeding when injuries occur. Without adequate vitamin K, the body cannot produce these factors effectively, leading to a higher risk of uncontrolled bleeding.

In the case of the other choices, vitamin A is primarily involved in vision, immune function, and skin health; vitamin D is crucial for calcium absorption and bone health; and vitamin C is important for collagen synthesis, antioxidant protection, and immune system support. While each of these vitamins has its unique functions, none of them directly contribute to the blood clotting process like vitamin K does.