In human nutrition, what is the main function of vitamin K?

• A. Acts primarily as an antioxidant to protect cell membranes from oxidative damage
• B. Regulates calcium and phosphorus absorption to maintain blood calcium homeostasis
• C. Supports vision by forming retinal pigments required for dark adaptation
• D. Serves as a cofactor for the carboxylation of clotting factors needed for normal blood coagulation

Answer: (D)

Verified step by step guidance

1. Identify the role of vitamin K in human nutrition by reviewing its biochemical functions.
2. Understand that vitamin K acts as a cofactor for the enzyme gamma-glutamyl carboxylase, which modifies certain proteins required for blood clotting.
3. Recognize that this carboxylation process enables clotting factors to bind calcium ions, which is essential for their activation and proper blood coagulation.
4. Differentiate vitamin K's function from other vitamins: it is not primarily an antioxidant, does not regulate calcium/phosphorus absorption like vitamin D, and does not support vision like vitamin A.
5. Conclude that the main function of vitamin K is to serve as a cofactor for the carboxylation of clotting factors, which is critical for normal blood coagulation.