Your liver uses vitamin K to produce a group of proteins called coagulation factors, which come together and form a blood clot if you sustain an injury. Coumadin blocks the action of vitamin K, decreasing the production of certain coagulation factors and reducing the clotting capacity of your blood. If you take Coumadin, you need to regulate your intake of vitamin K-rich foods because they may interfere with the action of the drug.
Spinach
Spinach contains a high concentration of vitamin K, with 1 cup of cooked spinach providing approximately 900 to 1,000 micrograms of vitamin K, according to the U.S. Department of Agriculture National Nutrient Database. Regulating your spinach intake does not mean you need to eliminate this nutritious vegetable from your diet. Rather, you want to eat approximately the same amount each week, explains the University of Michigan Health System.
Because Coumadin blocks the action of vitamin K, your dose must roughly match the amount of vitamin K in your diet to ensure an appropriate level of anticoagulation. If you suddenly increase your intake of spinach or another vitamin K-rich food, the surge of vitamin K may overwhelm the amount of Coumadin in your system. Production of the coagulation factors may increase, leading to loss of the blood-thinning effect of Coumadin, and a potentially life-threatening blood clot might form. Keeping your dietary vitamin K intake constant helps ensure that your blood stays properly anticoagulated while on Coumadin.
Kale
Kale is a member of the cabbage family of vegetables, which you may recognize by its distinctively ruffled leaves. Kale contains approximately 1,100 micrograms of vitamin K per cup, notes the USDA National Nutrient Database. Many restaurants use cooked kale as part of their recipes; you may want to ask your server about the ingredients if you are trying a new dish.
Greens
You can continue to enjoy eating greens while on Coumadin, provided you eat roughly the same amount each week. Greens include collards and turnip, mustard and beet greens, which contain roughly 500 to 1,000 micrograms of vitamin K per cup, according to the USDA National Nutrient Database. The National Institutes of Health recommends eating no more than 1/2 cup of cooked greens daily if you are taking Coumadin.
Brussels Sprouts, Endive and Romaine Lettuce
If you take Coumadin, the NIH recommends limiting your intake of Brussels sprouts, endive and Romaine lettuce to no more than three servings per day because these vegetables contain moderate concentrations of vitamin K. A serving size of cooked Brussels sprouts is 1/2 cup; one cup of raw endive or Romaine lettuce equals a single serving.
References
- "Chest"; Oral Anticoagulants: Mechanism of Action, Clinical Effectiveness, and Optimal Therapeutic Range; Jack Hirsh, M.D., et al.; January 2001
- USDA National Nutrient Database: Vitamin K (Phylloquinone) (mcg) Content of Selected Foods per Common Measure
- University of Michigan Health System: Warfarin (Coumadin), Patient Education Handout Associated with UMHS Clinical Care Guideline
- National Institutes of Health: Important Information to Know When You are Taking Coumadin and Vitamin K
- U.S. Department of Agriculture: What's in the Foods You Eat Search Tool, 4.1, Endive, Chicory, Escarole, or Romaine Lettuce, Raw
- Oregon State University Linus Pauling Institute: Vitamin K
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