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    Warfarin and Vitamin K

    Warfarin and Vitamin K

    Topic Overview

    Warfarin is a pill that you take regularly to help prevent blood clots or to keep a clot from getting bigger. Coumadin is the common brand name for warfarin.

    To ensure that warfarin is effectively thinning your blood, it's important to eat about the same amount of vitamin K every day.

    • Vitamin K normally helps your blood clot so wounds don't bleed too much.
    • Warfarin works against vitamin K, making your blood clot more slowly.

    So warfarin and vitamin K work against each other in your body. That is why, when you take warfarin, it's important that you not suddenly eat a lot more or a lot less vitamin K-rich food than you usually do.

    How to get a steady amount of vitamin K

    It's up to you how much vitamin K you choose to eat. For example, if you already eat a lot of leafy green vegetables, that's fine. Just keep it about the same amount each day.

    And if you take a multivitamin that contains vitamin K, be sure you take it every day.

    Check with your doctor before you make big changes in what you eat, such as starting a diet to lose weight.

    Adding vitamin K

    If you want to start eating more of a food that's rich in vitamin K, talk to your doctor about how to add it safely. Your warfarin dose may need to be adjusted.

    Use this list to get an idea of what foods are sources of vitamin K.

    Vitamin K content of select foods 1

    Food (no salt added)

    Serving Size

    Vitamin K (mcg)

    Kale, boiled, drained

    1 cup

    1062

    Spinach, frozen, boiled, drained

    1 cup

    1027

    Spinach, boiled, drained

    1 cup

    889

    Collards, boiled, drained

    1 cup

    836

    Broccoli, boiled, drained

    1 cup

    220

    Brussels sprouts, boiled, drained

    1 cup

    218

    Parsley, raw

    10 sprigs

    164

    Cabbage, boiled, drained

    1 cup

    163

    Spinach egg noodles, cooked, enriched

    1 cup

    162

    Spinach, raw

    1 cup

    145

    Broccoli, raw

    1 cup

    89

    Lettuce, green leaf, raw

    1 cup

    71

    Coleslaw, fast food

    cup

    70

    Okra, boiled, drained

    1 cup

    64

    Green peas, canned, drained

    1 cup

    63

    Lettuce (such as romaine), raw

    1 cup

    57

    Vegetables, mixed, frozen, boiled, drained

    1 cup

    43

    Lettuce, butterhead (such as Boston or Bibb), raw

    head

    42

    Blueberries, frozen, sweetened

    1 cup

    41

    Peas, edible pods, boiled

    1 cup

    40

    Green peas, frozen, boiled

    1 cup

    38

    Tuna fish, light, in oil, drained

    3 oz

    37

    Celery, raw

    1 cup

    35

    Lettuce, iceberg, raw

    head

    33

    Soy beans (edamame), boiled

    1 cup

    33

    Kiwi, raw

    1 medium

    31

    Scallion or spring onion, raw

    1 medium

    31

    Asparagus, boiled, drained

    4 spears

    30

    Blackberries, raw

    1 cup

    29

    Blueberries, raw

    1 cup

    28

    Marinara sauce for pasta, ready-to-serve

    cup

    18

    Cucumber, with peel, raw

    large

    12

    Canola oil

    1 Tbsp

    10

    Olive oil

    1 Tbsp

    8

    Pistachios, dry roasted, salt added

    1 oz (47 nuts)

    3.7

    Tea, brewed, prepared with tap water

    6 fl oz

    0.0

    Green and black tea leaves do contain vitamin K before they are steeped in water, but a small serving of the hot tea itself does not.

    Check with your doctor before you take any supplements or herbal products. Some of these may contain vitamin K. If you already take a product that contains vitamin K, do not stop taking it without talking with your doctor first.

    How vitamin K and warfarin affect your risks and your test results

    To find out how well warfarin is working, you will get blood tests to measure how long it takes for your blood to clot. Your lab results are called your Prothrombin Time (PT) and International Normalized Ratio (INR) values. You may just hear about your INR.

    Your INR needs to be in a safe range?not too high and not too low. Vitamin K can change how warfarin works, which changes your INR.

    • Vitamin K lowers your INR values. The lower your INR, the less time it takes for your blood to clot. A low INR means that warfarin isn't working well enough to prevent a dangerous blood clot.
    • Warfarin raises your INR values. The higher your INR, the more time it takes for your blood to clot. A high INR means that warfarin is working too well, so you bleed more quickly and easily. This can be dangerous.

    Keeping your warfarin and vitamin K intake steady every day helps keep you in a safe INR range.

    References

    Citations

    1. Agricultural Research Service (2010). USDA National Nutrient Database for Standard Reference, Release 23. Available online: http://www.ars.usda.gov/SP2UserFiles/Place/12354500/Data/SR23/nutrlist/sr23w430.pdf.

    Other Works Consulted

    • Agency for Healthcare Research and Quality (2010). Blood Thinner Pills: Your Guide to Using Them Safely (AHRQ Publication No. 09-0086-C). Rockville, MD: Agency for Healthcare Research and Quality. Available online: http://www.ahrq.gov/consumer/btpills.htm.

    Credits

    By Healthwise Staff
    E. Gregory Thompson, MD - Internal Medicine
    Rakesh K. Pai, MD, FACC - Cardiology, Electrophysiology
    Last Revised April 10, 2013

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