Q: My doctor has prescribed me Coumadin (warfarin) to fight blood clots. I see that youre supposed to avoid foods that contain large amounts of vitamin K when taking warfarin. Can you offer any more specific guidance as to what large amounts means?


Answer : We checked with Sarah L. Booth, PhD, director of the Vitamin K Laboratory at Tufts Jean Mayer USDA Human Nutrition Research Center on Aging, who shared the advice on warfarin and vitamin K shed recently reviewed for the Tufts-New England Medical Center: Vitamin K helps blood to clot, so it can change the way warfarin works. This does not mean you need to stop eating foods high in vitamin K, such as leafy green vegetables, which are also high in other heart-healthy nutrients. Your goal is to keep your diet consistent by eating the same amount of vitamin K foods from week to week. This will help warfarin to work its best. If you are not able to eat for a few days, or you are going to make big changes to your diet, call your doctor.

The rule of thumb is the greener the plant, the more vitamin K. You should aim to eat a similar mix of foods very high, high and medium in vitamin K daily. Foods very high in vitamin K (serving size 1/2 cup) include spinach, escarole, kale, seaweed, endive and collard greens. Turnip greens and Swiss chard are high in vitamin K. Medium foods include broccoli, Brussels sprouts, Romaine lettuce (1 cup), parsley (10 sprigs), green cabbage, spring onions, cole slaw, pistachios and mustard greens. Other vegetables and all fruits are low sources of vitamin K. Multivitamins and liquid nutrition supplements such as Ensure and Boost also contain vitamin K, so keep your use of these the same from week to week.

Also keep in mind that cranberry and grapefruit juice can increase warfarin in your blood; limit to four ounces per day. Vitamin E, fish oil supplements and alcohol in high amounts can change the way warfarin works. Herbal supplements should not be taken with warfarin. If in doubt, talk to your doctor.


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