A 72-year-old woman on long-term warfarin therapy for atrial fibrillation presents with spontaneous bruising, epistaxis, and a prolonged prothrombin time (PT 18 seconds, INR 4.2). She has been taking high-dose vitamin E supplements (1200 IU daily) for the past 6 months on the advice of a friend. Her dietary intake of leafy green vegetables has remained unchanged. Which of the following best explains the mechanism of her coagulopathy?