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 foods1

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

¾ 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

¼ 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

¼ 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

½ cup

18

Cucumber, with peel, raw

¼ 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
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Specialist Medical Reviewer Rakesh K. Pai, MD, FACC - Cardiology, Electrophysiology
Current as of March 12, 2014

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.

© 1995-2014 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.