What Foods Interact with Warfarin?

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Question: I was in the hospital when they found multiple bilateral pulmonary embolisms and would love to see an article on nutrition for someone who has to take Coumadin/warfarin. Greens and garlic and my favorite chamomile tea, lots of herbs, etc. effect how Coumadin works and would be awesome to see an article for folks like me. 

Answer: Coumadin, also known as warfarin, is an anticoagulant (blood thinning') medication that's usually used to prevent or treat blood clots.

Warfarin works by slowing down vitamin K activity and increases the time it takes for your blood to clot. 

Making significant changes in the amounts of vitamin K you consume in a short period can mess with your warfarin dosage, so it's important to speak with your doctor about the foods you eat. The goal is to keep your vitamin K intake at about the same amount every day.

The Institutes of Medicine says that the average person needs about 90 to 120 micrograms vitamin K per day – but if you’re taking warfarin, you should speak to your doctor about how much you need every day.

Foods High in Vitamin K

So, while I can't tell how much you should or should not consume, but I can tell you which foods are high in vitamin K. In general, foods highest in vitamin K are the dark green leafy vegetables. It’s important to note the difference between cooked and raw measurements. 

Cooked Greens

½ cup cooked kale -- 531 micrograms

½ cup cooked spinach -- 444 micrograms

½ cup cooked collards -- 418 micrograms

½ cup cooked Swiss chard h-- 287 micrograms

½ cup cooked turnip greens -- 265 micrograms

½ cup cooked mustard greens – 210 micrograms

½ cup cooked cabbage – 82 micrograms

Raw Greens

1 cup raw Swiss chard – 299 micrograms

1 cup raw mustard greens – 279 micrograms

1 cup raw collards – 184 micrograms

1 cup raw spinach – 145 micrograms

1 cup raw turnip greens – 138 micrograms

1 cup raw watercress – 85 micrograms

1 cup raw endive – 116 micrograms

1 cup green leaf lettuce – 71 micrograms

1 cup raw Romaine lettuce – 57 micrograms

¼ cup raw parsley – 246 micrograms

Other Foods

1 cup cooked broccoli – 220 micrograms

1 cup raw broccoli – 89 micrograms

1 cup cooked Brussels sprouts – 219 micrograms

1 cup cooked asparagus – 91 micrograms

1 cup stewed prunes 65 micrograms

1 cup avocado – 48 micrograms

3 ounces tuna – 37 micrograms

1 tablespoon soybean oil – 25 micrograms

1 tablespoon canola oil – 17 micrograms

Dietary Supplements

Some vitamin and mineral formulations contain vitamin K -- and you might find it in vitamin-fortified breakfast cereals, so read labels when you shop and don't take any dietary supplements before talking to your health care provider.


National Institutes of Health Office of Dietary Supplements. "Important information to know when you are taking: Warfarin (Coumadin) and Vitamin K." Accessed April 2, 2016. http://www.cc.nih.gov/ccc/patient_education/drug_nutrient/coumadin1.pdf.

Institute of Medicine of the National Academies. "Dietary Reference Intakes: Vitamins." Accessed April 2, 2016. http://iom.edu/~/media/Files/Activity%20Files/Nutrition/DRIs/DRI_Vitamins.pdf.

Oregon State University Linus Pauling Institute Micronutrient Research for Optimum Health. "Vitamin K." Accessed April 2, 2016. http://lpi.oregonstate.edu/infocenter/vitamins/vitaminK/.

United States Department of Agriculture Agricultural Research Service National Nutrient Database for Standard Reference, Release 28. Accessed April 2, 2016. https://ndb.nal.usda.gov/ndb/search.

The United States Food and Drug Administration. "Medication Guide Coumadin® (COU-ma-din) (warfarin sodium." Accessed April 2, 2016. http://www.fda.gov/downloads/drugs/drugsafety/ucm088578.pdf.

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