A 74-year-old woman with atrial fibrillation on warfarin is advised about diet. Which statement is most appropriate?

• A. Avoid leafy greens completely
• B. Maintain a consistent intake of foods containing vitamin K
• C. Take extra vitamin K weekly
• D. Stop foods containing vitamin K during treatment

Answer: (B)

Warfarin’s effect depends on vitamin K–dependent clotting factors, so changes in vitamin K intake can shift how anticoagulated you are. The safest, most effective dietary message is to keep vitamin K intake consistent. That way, the INR tends to stay within the target range, reducing the risk of bleeding if it rises or clotting if it falls.

Leafy greens and other greens are high in vitamin K, but you don’t need to avoid them entirely—you just need to eat them in a steady, predictable amount. Sudden increases or decreases in vitamin K can lead to unpredictable changes in anticoagulation, and adjusting the warfarin dose is then required.

Taking extra vitamin K or stopping vitamin K–containing foods would disrupt stability and is not advised. If you’re considering changes to your diet, discuss them with the prescriber and aim for a consistent pattern in vitamin K intake, with regular INR monitoring to adjust the warfarin dose if needed.