Ask The Doctors: November 2010
It is true that green leafy vegetables, including kale, collard greens, spinach, and broccoli, have a high vitamin K content. Warfarin thins the blood by interfering with the synthesis of certain coagulation factors, a vitamin K-dependent process. Eating large quantities of green leafy vegetables can tip the balance in favor of coagulation factor production, thus reducing the effectiveness of warfarin. However, a heart-friendly diet should include such vegetables, so complete abstinence would tend to make ones diet less healthy, as well as less tasty.