A 68-year-old on chronic warfarin therapy has a marked decrease in INR after starting a high‑kale diet. Which mechanisms explain this change, and how should therapy be adjusted?

• A. The change is unrelated to diet because dietary vitamin K cannot affect anticoagulant therapy; instead, suspect nonadherence to warfarin or an acute infection altering INR unpredictably.
• B. Kale contains large amounts of vitamin D which directly inhibits hepatic CYP450 enzymes that metabolize warfarin, producing a decreased INR; stop vitamin D supplements only.
• C. Kale contains vitamin E which potentiates warfarin leading to higher INR; therefore, discontinue kale immediately and start vitamin K injections to reverse the effect.
• D. Increased phylloquinone (K1) intake from kale increases gamma-carboxylation of clotting factors reducing warfarin effect; adjust warfarin dose downward or counsel to keep vitamin K intake consistent and monitor INR frequently.

Answer: (D)