Which vitamin is primarily involved in blood clotting?

Vitamin K plays a crucial role in the process of blood clotting. It is essential for the synthesis of certain proteins known as clotting factors, which are necessary for the coagulation process. This vitamin facilitates the conversion of these factors into their active forms, allowing them to function in promoting clot formation when there is a vascular injury.

Without adequate vitamin K, the blood clotting process can be severely impaired, leading to increased bleeding and difficulty in controlling hemorrhages. This function is so critical that vitamin K is often referred to as the "clotting vitamin."

In contrast, other vitamins listed have different functions: vitamin C is important for collagen synthesis and immune function, vitamin E acts as an antioxidant enhancing cellular protection, and vitamin A is primarily involved in vision and immune function. Thus, vitamin K's unique association with the blood coagulation cascade makes it the correct choice in this context.