Diet and warfarin
The cabbage family is high in vitamin K, and can affect your INR. Image: Shutterstock.com
Certain foods and drinks can interact with warfarin and change the way it works. The most important thing is to be consistent in the types of foods and amounts you eat — don’t make drastic changes on a day-to-day basis. Get to know which foods can affect how warfarin works, so that you can eat consistent quantities of these each day.
- If your diet changes (or you want to make changes to it), get advice from your doctor or pharmacist. You may need extra blood tests to check your INR.
- Tobacco smoking can affect your International Normalised Ratio (INR). Quitting smoking has many benefits, but let your doctor know if you do quit, as you might need to have your INR checked.
- Avoid crash diets or binge eating. This may affect your INR.
- If you are sick and don’t feel like eating for a few days, this may affect your INR. Any new medicines that you may be taking when you are ill may also affect your INR. Let your doctor know if you are unwell or if you are taking any new medicines.
- Limit alcohol intake.
Watch our video, in which Dr John Worthington explains why he recommends that people taking warfarin should eat some foods containing vitamin K (e.g. green leafy vegetables) — but to keep the amount stable to avoid problems.
Alcohol can also interact with warfarin to increase the risk of bleeding — it is best to limit alcohol intake and avoid binge drinking. One to two standard drinks of alcohol per day may be permitted but this may depend on how stable your INR is, and other factors. Discuss the amount of alcohol you can have with your doctor.
In the following video, Dr John Worthington explains the safety advice for alcohol and warfarin, and reminds us of the importance of having some alcohol-free days every week.
Eat consistent amounts of green leafy vegetables
You can eat green leafy vegetables if you are taking warfarin. But it’s important to eat the same amount of these foods each week to help keep your INR stable. This is because green leafy vegetables (e.g. spinach, broccoli, Brussels sprouts) are rich in vitamin K, which can affect your INR.
Don’t avoid vitamin K-rich foods completely — vitamin K is essential to our health. Studies show that eating regular, consistent amounts of vitamin K-rich foods is better for maintaining a stable INR, than not eating them at all, or eating varying amounts.
Other vitamin K-containing foods
Many other fresh and pre-packed foods contain varying amounts of vitamin K. The nutritional content of pre-packaged food and drinks is usually described on the label, however vitamin K information is not always included. This can make it difficult for you to know how much vitamin K pre-prepared foods contain.
Find out more about the amount of vitamin K different foods contain.
Ask a doctor or pharmacist if you are unsure if a particular type of food or drink can interact with warfarin, or affect your INR.
Drinking large amounts of cranberry juice may increase the risk of bleeding in some people taking warfarin. However, drinking 250 mL (1 cup) or less of cranberry juice is unlikely to affect your INR or pose any risk of bleeding.
- Unit for Medication Outcomes Research and Education (UMORE). About Warfarin, Healthy Lifestyle, Diet. Tasmania: University of Tasmania. www.anticoagulation.com.au/AboutWarfarin/HealthyLifestyle/Diet/tabid/116/Default.aspx (accessed 9 May 2012).
- Aspen Pharma Pty Ltd. Dietary guidelines and drug-herb interactions for people taking Warfarin. www.aspenpharma.com.au/product_info/Warfarin_Dietary_Guidelines.pdf (accessed 9 May 2012).
- Cambria-Kiely, JA. Effect of soy milk on warfarin efficacy. Ann Pharmacother 2002; 36: 1893-6.
- United States Department of Agriculture. Agricultural Research Service. Food and Nutrition Information Centre. National Nutrient Database for standard references, Release 25. Vitamin K (phylloquinone) content of selected foods.