Vitamin K controls and prevents bleeding by enabling the production of clotting factors in your blood. Clots traveling through the blood vessels can cause a heart attack or a stroke. Coumadin, also known as warfarin, is an anticoagulant, or blood-thinning medication, used to control how fast blood clots by reducing the effect of vitamin K. Dietary restrictions apply to foods, drinks, vitamins and herbal supplements that interfere with the effectiveness of coumadin.
Vegetables
Foods high in vitamin K, such as dark green leafy vegetables, can cause fluctuations in the therapeutic effectiveness of Coumadin. Do not eliminate them from your diet, because they are high in fiber and provide necessary nutrients. If you consume these vegetables on a regular basis, maintain level amounts of vitamin K in your bloodstream by keeping your consumption consistent. The average daily allowance of vitamin K for adult men and women is 120 mcg and 90 mcg, respectively. My.ClevelandClinic.org recommends limiting daily consumption to one-half cup cooked dark green vegetables or 3 oz. raw vegetables. Dark green vegetables to limit include cabbage, broccoli, Brussels sprouts, spinach, escarole, turnip greens and lettuce -- excluding iceberg lettuce. Also limit cauliflower, which is not green but is in the broccoli family. Vegetables low in vitamin K include green beans, peas, carrots, cucumbers, eggplant, tomatoes, potatoes, celery and corn.
Herbal Products
NYU Medical Center offers a list of herbal products that cause interactions with Coumadin. The products to avoid include alfalfa, black cohosh, bromelain, celery, chamomile, fenugreek, garlic, ginger, ginkgo biloba, horseradish, licorice, onion and parsley. Drugs.com suggests you avoid cranberries, cranberry juice and herbal products containing cranberries.
Beverages
Beverages to limit or avoid when you're taking Coumadin include green tea and herbal teas containing tonka beans, sweet clover or sweet woodruff. MayoClinic.com recommends you avoid cranberry juice or consume it in small amounts because it can increase the effect of Coumadin. Alcohol also alters Coumadin's effectiveness and can increase side effects, according to Drugs.com. If you drink alcoholic beverages on a regular basis, you doctor will help you establish a safe limit.
Dietary Supplements and Vitamins
Dietary supplements containing vitamin K include Ensure, Boost and Carnation Instant Breakfast. If you take supplements, keep consumption consistent to avoid fluctuations in your vitamin K levels.
Vitamins that may affect your International Normalized Ratio or INR, which is used to measure the effects of warfarin, include vitamin C at doses greater than 500 mg/day, which can lower INR. Vitamin E in doses higher than 400 IU/day can elevate your INR level. Multivitamins contain small amounts of vitamin K. The NYU Medical Center recommends taking multivitamins consistently if you do take them. Before making changes that introduce new products into your diet, consult your physician.
Monitoring Coumadin
Coumadin has a narrow range of effectiveness, which is why routine monitoring is necessary. The range of effectiveness, or the therapeutic range, is affected by changes in diet, medication or illness. Monitoring requires an INR blood test. NYU Medical Center explains the average therapeutic range is 2.0 to 3.0 and increases to 2.5 to 3.5 for patients with heart valve replacements. Your physician can determine a more specific range if warranted by your individual condition. Test results showing a lower INR level than that set by your doctor indicate your blood is too thick, which can cause you to develop blood clots. A higher INR reading means you are at risk of bleeding because your blood is too thin. Fluctuations in INR levels require an adjustment in your Coumadin dose.
