If you take blood thinners daily, your health-care provider might advise you to restrict your intake of foods high in vitamin K. Blood thinners such as warfarin lengthen clotting time in people who are at risk for developing internal blood clots, and foods rich in vitamin K, which enables a chain of chemical reactions that allows your blood to form clots to stop abnormal bleeding, might interfere by shortening your clotting time. Consuming these foods on a limited, consistent basis can help keep your clotting time within a range that's safe for you.
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Blood clotting is a vital response to excessive bleeding, but the formation of clots in your blood vessels can block circulation to your heart, lungs and brain. Blood-thinning medications, or anticoagulants, prevent your blood from forming clots too quickly. Two common laboratory tests, the international normalized ratio, or INR, and prothrombin time, or PT, measure the clotting time of your blood. Consuming excessive quantities of foods or beverages that are rich in vitamin K can speed up clotting time and make these values fall outside of the desired range.
Vitamin K is a fat-soluble nutrient that your body stores in fatty tissues. A certain amount of vitamin K also is produced naturally by bacteria in your digestive tract. The Institute of Medicine recommends that adults over 19 get 90 micrograms of vitamin K per day from dietary sources or supplements. To keep your PT/INR within your desired range, consult your health-care provider about how much dietary vitamin K you can safely consume each day.
Dark green, leafy vegetables such as spinach, kale, collard greens, chard and parsley are high in vitamin K. Cauliflower, soybeans and some cereals provide vitamin K. Green tea and vegetable oils such as olive and canola also contain this essential nutrient.
Omitting foods high in vitamin K from your diet could deprive you of some of their other nutritional benefits. Vegetables such as kale, collard greens and spinach offer vitamins A and C and essential minerals such as iron, calcium and potassium. Research indicates that chemicals in cruciferous vegetables such as broccoli, cauliflower and kale play a role in preventing cancer, according to the Linus Pauling Institute. In addition to its role in blood clotting, vitamin K also helps maintain bone mass by allowing calcium to bind to bone.
The National Institutes of Health advise eating no more than three servings per day of foods that contain 60 percent to 199 percent of the recommended daily value of vitamin K. This group includes broccoli, spinach and romaine lettuce. Eat no more than one serving per day of foods that contain more than 200 percent of the daily value of vitamin K, including mustard greens, Swiss chard and kale. Work with your health-care provider to include these nutrient-dense foods in your diet without compromising your health.