Vitamin K Affects Your Body’s Ability to Metabolize Warfarin

Several foods, medicines, and herbal supplements can interact with warfarin and impact its effectiveness. It is important that you are aware of these interactions so that you can manage your therapy properly.

When you start warfarin, tell your healthcare provider about your eating patterns and any nutritional or herbal supplements, including herbal teas, that you take regularly. If your healthcare provider says that you may continue taking the supplements, remember the importance of consistency in both your eating pattern and in taking your supplements.

While you are taking warfarin, let your healthcare provider know before you change your nutritional supplements or eating pattern. This will allow your healthcare provider to monitor your condition and adjust your warfarin as needed.


People with multiple risk factors for blood clots are at increased risk of clots compared to people with only one risk factor. Because people with several risk factors need special consideration, it is normal for healthcare professionals to perform a complete evaluation when a patient experiences their first blood clot. This is particularly important for children.

Additionally, warfarin should not be used during pregnancy because it may harm the growing fetus. Talk to your doctor about your treatment plan if you are pregnant or planning to become pregnant.


What Does Vitamin K Do in the Body?

The body needs vitamin K to produce some essential blood clotting factors. Without enough vitamin K, these clotting factors may still be produced but are ineffective in clotting. Therefore, people with too little vitamin K have a bleeding tendency.

How Does Warfarin Interact with Vitamin K?

Warfarin interferes with the action of vitamin K and therefore prolongs the time it takes to form a clot. This is the intended effect of this therapy. Increasing vitamin K intake while you are on warfarin will work against the action of this medication.

Why Do I Have to Keep My Vitamin K Level Consistent?

It is very important to keep the amount of vitamin K in your diet the same while on warfarin. Variations in vitamin K levels may cause your prothrombin time/international normalized ratio test, the laboratory test that measures the effect of warfarin, to change. You do not need to stop eating foods that contain vitamin K. However, you should be aware of foods that are very high in vitamin K, and you should try to keep the amounts the same every day.

Learn more about the prothrombin time/international normalized ratio test

How Much Vitamin K Do I Need?

The average person in the United States takes in 60 to 80 micrograms (mcg) of vitamin K per day. This is a very tiny amount (60 to 80 millionths of a gram). Extremely small changes in vitamin K intake can have a major effect on the prothrombin time/international normalized ratio test in some patients on warfarin.

It is not necessary for most people to count the amount of vitamin K that they eat every day while on warfarin. If, however, you are having difficulty stabilizing your prothrombin time/international normalized ratio, you may benefit from writing down your daily intake of vitamin K to make sure that it is the same every day.

Varying the amount of vitamin K in your diet can change the effectiveness of warfarin, so aim for consistency. Eat a balanced diet with a variety of foods. For instance, if your normal pattern is to have two servings per day of food high in vitamin K, then make sure to continue with this pattern every day. If you do not normally eat these foods, do not suddenly eat a large amount of them.

What If I Want to Make a Change in My Diet?

When you start taking warfarin, eat your usual amount of vitamin K-containing foods while your doctor finds the right dose for you. While you are taking warfarin, be sure to tell your doctor if you change your diet or change your eating pattern because this is likely to change your vitamin K intake.

Your doctor can monitor your prothrombin time/international normalized ratio test closely when your diet changes and can adjust your warfarin as needed. Doing any of the following may influence the amount of vitamin K in your body:

  • Increasing your vegetable intake as part of a diet to lose weight

  • Eating more fresh vegetables in spring and summer because of the larger selection available

  • Being sick and unable to eat solid foods for a few days

  • Returning to your normal diet after being hospitalized and on a limited diet due to surgery or illness

  • Changing your diet due to traveling to a place where the foods are unfamiliar

  • Deciding to change your diet to eat more lentils, beans, dried peas, and vegetables

Get a list of foods containing vitamin K