Food-Nutrient Interactions with Coumadin/Warfarin

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The Role of Vitamin K

How is the medication Coumadin/Warfarin affected by my diet?

Coumadin/Warfarin is a medication prescribed to prevent or treat people who are at increased risk of form- ing blood clots that can prohibit the flow of blood to the heart or brain. These harmful blood clots can form in any blood vessel in the body and even the lungs. Vitamin K is the main dietary component that a patient needs to pay close attention to while taking Coumadin/Warfarin. The major role vitamin K plays in the body is to help make proteins that cause the blood to clot when a person bleeds.

What effect does vitamin K have on Coumadin/Warfarin?

Coumadin, a brand name or Warfarin, a generic version is categorized as an anticoagulant or blood thinner, which extends the time for blood clots to form. If a patient taking Coumadin/Warfarin lacks the recommended amount of vitamin K, their blood can become dangerously thin and cause hemorrhaging. If a person consumes an excessive amount of vitamin K, the effective- ness of Coumadin/ Warfarin in the blood- stream will decrease. The blood will coagulate too quickly, which contradicts the drug action of slowing down blood clotting.

It is recommended that patients often have blood drawn to measure the time it takes for the blood to clot. These blood tests will allow the doctor to know if the correct amount of Coumadin/Warfarin is being prescribed. A consistent intake of vitamin K food sources is recommended to keep the coagulation time steady and predictable.

What foods are excellent sources of Vitamin K?

Nutrition therapy includes eating a well balanced diet and a constant intake of foods that contain vitamin K. Foods that provide an excellent source of vita- min K are green, leafy vegetables. Dietitians recommend patients who are prescribed Coumadin/Warfarin to eat no more than three servings of green, leafy vegetables daily.

These three servings include one serving of foods high in vitamin K and two servings of foods moderately-high in vitamin K. Foods high in vitamin K include one half cup of cooked spinach, cooked turnip greens, and cooked collards. Foods that are moderately high in Vitamin K include one cup of raw spinach, raw endive lettuce, raw romaine lettuce, raw broccoli, one half cup of cooked Brussels Sprouts, or cooked cabbage.

Special points of interest:

  • Foods sources of vitamin K include: liver, broccoli, Brussels Sprouts, spinach, collards, cabbage, and other green, leafy vegetables.
  • In general, patients do not need to worry about consuming an excessive amount of green vegetables, but rather focus on eating a consistent amount of vegetables.
  • One cup of raw vegetables or a half cup of cooked vegetables is considered one serving of vegetables. While two cups of raw leafy, greens is considered one serving of vegetables.

References: Nutrition Care Manual;; Drug Information Online. Nutrition Education for NOVEMBER 2008. Produced by Meals On Wheels, Inc. of Tarrant County by Kaitlynn Jacobson, a nutrition intern for Sherry Simon, R.D./L.D. For questions regarding nutritional information, please contact Sherry Simon, R.D./L.D., Director of Nutrition Services for Meals on Wheels, Inc. Tarrant Country at (817) 336-0912 or email:

Posted in Nutritional Education.

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