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How Green, Leafy Vegetables Affect Coumadin

author image Michelle Kerns
Michelle Kerns writes for a variety of print and online publications and specializes in literature and science topics. She has served as a book columnist since 2008 and is a member of the National Book Critics Circle. Kerns studied English literature and neurology at UC Davis.
How Green, Leafy Vegetables Affect Coumadin
A small bowl of brussels sprouts with slivered almonds on top. Photo Credit: Szakaly/iStock/Getty Images

Your doctor might prescribe Coumadin if you have or are at high risk for developing a blood clot, which could cause a stroke, a lung embolism or deep-vein thrombosis in your limbs. While taking Coumadin, a brand name for the prescription drug warfarin, you must monitor your daily intake of green, leafy vegetables. The vitamin K content in these vegetables could affect how Coumadin works in your body.

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The Vitamin K Effect

Your body uses vitamin K to synthesize four of the 13 proteins that your body needs to coagulate, or clot, blood properly. Coumadin works to prevent blood-clot formation by blocking production of these vitamin K-dependent proteins. So if you're using Coumadin and boost your intake of foods rich in vitamin K, that might lower your international normalized ratio, the standard measure of how long it takes blood to clot. A low ratio could raise your risk of developing blood clots.

Vitamin K Content

Some of the richest natural sources of vitamin K are green, leafy vegetables. For example, cooked spinach provides 888 micrograms and cooked Swiss chard supplies 572 micrograms in every cup. Adult men need only 120 micrograms of vitamin K a day; women require about 90 micrograms. One cooked serving of spinach, chard or another green, leafy vegetable, such as leaf lettuce, kale, collard greens or brussels sprouts, far exceeds the average adult's recommended daily allowance.

Recommended Intake

You still need to consume adequate vitamin K each day, even when you're taking Coumadin, advises the Palo Alto Medical Foundation. You should, however, limit your intake of high-vitamin K foods to one serving a day. You can have up to three servings of foods moderately high in vitamin K -- raw broccoli or spinach and romaine, endive or green leaf lettuce -- each day.

Expert Insight

The key to getting the maximum benefit of vitamin K without affecting the function of Coumadin is to eat a consistent amount of the nutrient. Continue to eat the same amount of green, leafy vegetables after you begin taking Coumadin as you did before. Make sure your doctor is aware of your intake so that your dose of the drug can be adjusted accordingly. Do not significantly increase the amount of green, leafy vegetables in your diet without first discussing the change with your doctor.

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