Vitamin K-rich foods can influence warfarin therapy. Which statement best describes this effect?

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

Answer: (B)

Vitamin K–rich foods can counteract warfarin’s anticoagulant effect. Warfarin works by limiting the activation of vitamin K–dependent clotting factors, which prolongs clotting time and raises the INR. When you consume foods high in vitamin K, you provide more vitamin K to the body, allowing more clotting factors to be produced, which reduces warfarin’s impact. This shows up as a lower INR, meaning less anticoagulation. For that reason, increasing dietary vitamin K tends to decrease warfarin’s effect, while very low intake can raise the INR. In practice, patients are advised to keep vitamin K intake consistent to avoid fluctuations. Hence, the statement that best describes the effect is that vitamin K-rich foods can decrease warfarin’s effect by reducing INR.