Spinach, kale, collard greens, and broccoli are very healthy, but they can make medicines to prevent blood clots less effective. Green leafy vegetables are rich in vitamin K, which interacts with the common blood thinner drug warfarin (Coumadin). Vitamin K is used by the body to make certain blood clotting factors, while warfarin reduces the action of vitamin K.
Tasha Woodall, associate director of geriatric drug therapy at Mountain Area Health Education Center in Asheville, NC, often talks about workarounds for patients taking medications like warfarin. “I often tell people, you really don’t need to avoid eating green leafy vegetables. They are definitely good for you. But the key is to be consistent.”
Patients taking warfarin have their blood levels checked regularly. “I have certainly taken care of people on warfarin who have been stable for a long time and who eat spinach, kale, collard greens with every meal of the day,” says Woodall, who is also an associate professor of clinical education at UNC Eshelman School of Pharmacy. “The problem arises when someone eats a spinach salad every day for a few weeks until the bag of spinach is used up, then leaves again the next week without eating it.” Instead, predictable consumption allows medication to be adjusted accordingly.