Deficiency of which vitamin leads to hemorrhage and bruising?

• A. Vitamin K
• B. Vitamin E
• C. Vitamin A
• D. Vitamin D

Answer: (A)

Deficiency of vitamin K disrupts the production of functional clotting proteins. Vitamin K is required to gamma-carboxylate glutamate residues on clotting factors II, VII, IX, and X, as well as the anticoagulant proteins C and S. This modification allows these proteins to bind calcium and phospholipid surfaces, enabling the coagulation cascade to proceed. Without enough vitamin K, these factors become inactive, leading to impaired clot formation, easy bleeding, and bruising. Clinically, this often shows up as a prolonged clotting time. The other vitamins have different roles—E is mainly an antioxidant with neuropathy risk in deficiency, A affects vision and skin, and D affects bone health—so they are not primarily linked to hemorrhage and bruising.