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.

Sources:

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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