What is the primary function of vitamin K?

• A. Antioxidant activity
• B. Energy production
• C. Synthesis of seven blood clotting factors
• D. Calcium absorption

Answer: (C)

Vitamin K enables the synthesis (activation) of seven clotting-related proteins by acting as a cofactor for the enzyme that gamma-carboxylates glutamate residues on these factors. This post-translational modification lets the clotting proteins bind calcium and interact with phospholipid surfaces, which is essential for them to participate effectively in the coagulation cascade. Without this carboxylation, these factors cannot function properly, leading to impaired blood clotting and bleeding risk. The other options don’t describe the main role: antioxidant activity isn’t the primary job, energy production is handled by other nutrients, and calcium absorption is mainly linked to vitamin D.