Skip to Content

Warfarin and Vitamin K

Skip to the navigation

Topic Overview

Warfarin is a pill that you take regularly to help prevent blood clotsor 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 foodsfootnote 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

773

Broccoli, boiled, drained

1 cup

220

Brussels sprouts, boiled, drained

1 cup

218

Cabbage, boiled, drained

1 cup

163

Spinach egg noodles, cooked, enriched

1 cup

162

Spinach, raw

1 cup

145

Coleslaw, fast food

1 cup

135

Broccoli, raw, chopped

1 cup

93

Asparagus, boiled, drained

1 cup

92

Okra, boiled, drained

1 cup

64

Green peas, canned, drained

1 cup

63

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

1 cup

56

Lettuce (such as romaine), raw

1 cup

48

Lettuce, green leaf, raw

1 cup

46

Vegetables, mixed, frozen, boiled, drained

1 cup

43

Blueberries, frozen, sweetened

1 cup

41

Peas, edible pods, boiled

1 cup

40

Green peas, frozen, boiled

1 cup

38

Celery, raw

1 cup

30

Blackberries, raw

1 cup

29

Blueberries, raw

1 cup

29

Marinara sauce for pasta, ready-to-serve

½ cup

18

Lettuce, iceberg, raw

1 cup

17

Canola oil

1 Tbsp

10

Cucumber, with peel, raw

½ cup

9

Olive oil

1 Tbsp

8

Tuna fish, white, canned in oil, drained

3 oz

6

Kiwi, raw

1 fruit

5

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.

Health Tools

Health Tools help you make wise health decisions or take action to improve your health.

Actionsets are designed to help people take an active role in managing a health condition.

References

Citations

  1. Agricultural Research Service (2015). USDA National Nutrient Database for Standard Reference, Release 28. Available online: https://ndb.nal.usda.gov/.

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

ByHealthwise Staff
Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine
Martin J. Gabica, MD - Family Medicine
Adam Husney, MD - Family Medicine

Current as ofDecember 6, 2017

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 and Privacy Policy. Learn how we develop our content.

© 1995-2018 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.

Symptom Checker

Feeling under the weather?

Use our interactive symptom checker to evaluate your symptoms and determine appropriate action or treatment.

Symptom Checker

Decision Points

Our interactive Decision Points guide you through making key health decisions by combining medical information with your personal information.

You'll find Decision Points to help you answer questions about:

Interactive Tools

Get started learning more about your health!

Our Interactive Tools can help you make smart decisions for a healthier life. You'll find personal calculators and tools for health and fitness, lifestyle checkups, and pregnancy.