Dietary advice for patients taking warfarin

The aim of this leaflet

You have been given this leaflet because you are on warfarin.

Warfarin is an anticoagulant medication (sometimes called a blood thinner), which prevents the formation of harmful blood clots in your blood vessels. It is used in the treatment of conditions in which blood clots are more likely to form. Warfarin increases the time it takes for your blood to clot (thicken) by interfering with how the body uses vitamin K.

A blood test called an INR (international normalised ratio) is used to measure how long your blood takes to clot; the longer your blood takes to clot, the higher your INR. Your warfarin dose will depend on your INR result. If your INR result is outside the target range appropriate for your condition, the dose of warfarin will be increased or decreased accordingly.

The aim of this leaflet is to give you dietary advice about how to manage the amount of vitamin K you eat.

What can affect the control of my anticoagulation?

The INR result can be affected by:

• diet – specifically vitamin K content
• alcohol intake – please discuss with your doctor or pharmacist
• other medications (including prescription medicines, over the counter medicines, supplements and alternative/ herbal remedies for example St John’s Wort) and health conditions – please discuss with your doctor or pharmacist to advise which medicines and supplements are safe to take alongside warfarin
• pregnancy – discuss with your doctor before trying to conceive

Dietary advice

Vitamin K helps your blood to clot and is found in the food we eat. Foods containing vitamin K add variety and other benefits to your diet and you do not need to avoid them entirely. However, it is important to consume a consistent amount of such food. This will ensure your vitamin K levels remain constant and your INR result and warfarin dose are more likely to remain stable.

Significantly increasing or decreasing your intake of foods containing vitamin K on a day-to-day or week-to-week basis may affect your INR result and your risk of clotting or bleeding. Please discuss with your doctor before making any significant changes to what you eat, for example before starting a diet to lose weight, or becoming vegetarian or vegan.

Which foods contain vitamin K?

• green leafy vegetables (asparagus, spinach, kale, broccoli, cabbage, lettuce, parsley, brussels sprouts, swiss chard, watercress, green beans)
• pine nuts and mungo beans
• fruits such as blackberries, blueberries, kiwi fruit, avocado, raisins
• vegetable oils (soybean oil, canola oil)
• egg yolks (and products containing them such as mayonnaise)
• liver (all types)
• fermented foods e.g. natto, mature and blue cheeses
• soy products (edamame and soybeans) and chickpeas

What about drinks?

Green tea contains a small amount of vitamin K. As with the advice above, if you drink green tea you should do so consistently, and avoid suddenly stopping/ starting to drink it.

Despite not being as high in vitamin K as some other foods/ drinks, the following may cause changes to your INR by altering how warfarin is removed from the body. Avoid these entirely while taking warfarin:

• cranberry juice and cranberry products (including capsules or concentrates)
• grapefruit juice
• pomegranate juice

For further advice, please contact:

Addenbrooke’s Outpatient Anticoagulation Service

Box 217
Addenbrooke’s Hospital
Hills Road
Cambridge
CB2 0QQ

Tel: 01223 217127

Open: Monday to Friday 09:00 to 17:00 hours.