Coumadin, also known as Warfarin, is an anti-coagulant prescribed to treat and prevent blood clots as well as stroke and heart attacks. Certain foods reduce the effectiveness of this blood-thinning medication, so pay attention to what you’re eating. For example, Coumadin has a significant nutrient-drug interaction with vitamin K, which is a crucial player in the blood clotting mechanism.
When large amounts of foods high in vitamin K or vitamin K supplements are taken with Coumadin or you alter the amount consumed, Coumadin’s anti-coagulant effectiveness is reduced and the amount of Coumadin needed is increased. On the other hand, greatly lowering your intake may increase the effect. Therefore, vitamin K intake should be consistent in order to maintain the levels of Coumadin within a stable, therapeutic level.
The National Institutes of Health recommends keeping your intake of vitamin K consistent by limiting your intake of foods considered high in vitamin K to no more than 1 serving per day and foods with moderate amounts of vitamin K to no more than 3 servings per day.
Green, leafy vegetables are very rich dietary sources of vitamin K, including kale, spinach, collard, turnip and mustard greens, Swiss chard and parsley. You do not need to cut these sources out of your diet; instead, do not significantly change your normal consumption. Eat the same amount every day and from week to week. Other vegetables that are moderately high in vitamin K include asparagus, broccoli, avocado, Brussels sprouts, cabbage, cauliflower, endive, escarole, lettuce, scallion, purple seaweed and watercress. Vegetables low in vitamin K are carrots, potatoes, tomatoes, peppers and corn.
Beans and Fats
Chickpeas, lentils, mung beans and soybeans are also high in vitamin K. Avoid eating excessive amounts of these foods, and instead try to maintain a consistent intake. Various oils are also sources of vitamin K, including canola, fish and soybean oils, as are mayonnaise and pistachio nuts.
Green tea, liver, cranberry and cranberry juice, kiwi, mango, and alcohol can also affect Coumadin effectiveness. Cranberry juice can increase the effect of Coumadin, leading to bleeding problems. Ingesting more than 3 drinks daily of alcohol may increase certain side effects of Coumadin because both alcohol and Coumadin are metabolized in the liver. Consult your doctor for more information on these food-drug interactions.
In addition, feverfew, garlic, ginkgo biloba, ginger, licorice, red clover, cayenne, St. John's wort, wheat grass and omega-3 fatty acids can also affect blood coagulation. Consumption of any of these dietary supplements may necessitate a change in the dosage of Coumadin. Ensure, Boost and Carnation Instant Breakfast also contain vitamin K. If you are taking these, maintain a consistent intake. Consult your doctor before taking any dietary supplements.
- Nutrition Therapy and Pathophysiology; Marica Nelms et al.
- National Institutes of Health: Important Information to Know When You Are Taking Coumadin and Vitamin K
- University of Michigan Hospitals and Health Centers: Warfarin/Coumadin