Blood thinners can save your life if your blood clots too easily. When you take the blood thinner warfarin, blood tests to monitor your blood clotting are a frequent addition to your to-do list, including INR, which stands for International Normalized Ratio. Foods high in vitamin K can interfere with the effectiveness of warfarin, so keeping your vitamin K intake stable lets warfarin work as intended to prevent life-threatening clots from forming.
INR and Blood Thinners
When you're on warfarin, you'll be seeing the phlebotomist frequently, generally at least once a month. Doctors use two lab tests to measure the effectiveness of blood thinners: the INR and prothrombin time. Prothrombin time measures the amount of time it takes for blood to clot in seconds. The INR compares your clotting time to those of a person not taking warfarin, whose INR is expressed as 1.0. The goal of warfarin therapy is to keep the INR between 2 and 3, according to MayoClinic.com. If your INR is too high, you can bleed too easily and too long after minor injuries.
Vitamin K Effects
Vitamin K is one of your body's major players in producing clotting factors, which keep you from bleeding to death when you cut yourself. Fortunately, you can get vitamin K in two ways: many foods contain vitamin K, but your body can also make its own supply. The blood thinner warfarin interferes with the way your body uses vitamin K and slows down your blood's ability to clot, which is its intended effect. If you increase your vitamin K intake, you might need higher doses of warfarin to counteract the effect of vitamin K. Your doctor will probably recommend keeping your vitamin K intake between the recommended adequate intake of 90 to 120 micrograms per day.
Foods High in Vitamin K
Leafy green vegetables like broccoli, kale, spinach, Swiss chard, parsley and iceberg lettuce are high on the nutritional health list, but they're also at the top of the vitamin K chart, with more than 200 micrograms of vitamin K per serving. Brussels sprouts, onions, asparagus and cabbage are also good sources of vitamin K, with more than 70 micrograms per serving. Liver also contains large amounts of vitamin K, but since many people don't like liver, you might not mind crossing it off your shopping list. Greens such as collard, dandelion, turnip or mustard greens are an acquired taste, but if you love them, eat them in moderation; a 1-cup serving contains over 800 micrograms of vitamin K.
How To Manage Vitamin K Intake
You don't have to permanently cross foods that contain vitamin K off the menu. In fact, keeping your vitamin K intake consistent is more important than avoiding the nutrient. When you heap your plate full of vegetables containing vitamin K one day and don't put anything green on your plate the next, your warfarin dose might be adequate the first day but too low or high the second. Maintaining a steady dose of vitamin K from your diet each day makes it easier for your doctor to regulate your warfarin dose so it's effective for you. Follow your doctor's recommendations on how much vitamin K is good for you and let him know if you notice that you're bruising more or less easily than you usually do.
- Linus Pauling Institute: Vitamin K
- MayoClinic.com: Prothrombin Time Test
- U.S. Department of Health and Human Services: Blood Thinner Pills Your Guide to Using Them Safely
- The National Alliance for Thrombosis and Thrombophilia: Vitamin K and Warfarin(Coumadin)
- National Institutes of Health: Important Information to Know When You Are Taking: Coumadin and Vitamin K
- Vaughns Summaries: High Vitamin K Foods
A registered nurse with more than 25 years of experience in oncology, labor/delivery, neonatal intensive care, infertility and ophthalmology, Sharon Perkins has also coauthored and edited numerous health books for the Wiley "Dummies" series. Perkins also has extensive experience working in home health with medically fragile pediatric patients.