Which statement about vitamin K-rich foods and warfarin is true?

Which statement about vitamin K-rich foods and warfarin is true?

• A. Vitamin K-rich foods can decrease warfarin's effect by reducing INR
• B. Vitamin K-rich foods can increase warfarin's effect by raising INR
• C. Vitamin K-rich foods have no effect on INR
• D. Vitamin K-rich foods unpredictably alter INR

Answer: (A)

Warfarin reduces the production of vitamin K–dependent clotting factors, so the level of anticoagulation is tracked by the INR. When you consume vitamin K–rich foods, you supply more vitamin K, which replenishes those factors and counteracts warfarin’s effect. This tends to lower the INR, meaning less anticoagulation. So vitamin K–rich foods can decrease warfarin’s effect by reducing INR. The other statements don’t fit: higher INR would come from less vitamin K, and while intake can influence INR, the direction is predictable rather than truly unpredictable when intake is considered.

Warfarin reduces the production of vitamin K–dependent clotting factors, so the level of anticoagulation is tracked by the INR. When you consume vitamin K–rich foods, you supply more vitamin K, which replenishes those factors and counteracts warfarin’s effect. This tends to lower the INR, meaning less anticoagulation. So vitamin K–rich foods can decrease warfarin’s effect by reducing INR. The other statements don’t fit: higher INR would come from less vitamin K, and while intake can influence INR, the direction is predictable rather than truly unpredictable when intake is considered.