A common concern many heart patients first share is their diet concern following a cardiac event. Blood thinners are very commonly prescribed for heart conditions such as atrial fibrillation, or post valve replacements. Many are told to be careful about leafy green vegetables. What the heck does be careful mean? Many take it to mean they can’t eat green vegetables, but then question how they are to eat a healthy diet. This is a very common misconception. It is important to get vitamin K in the diet, and the goal if taking coumadin/warfarin is to get the approximate same intake each day. This is very difficult to do, thus INR levels are fluctuate greatly and this creates health issues if not closely monitored. Most doctors aim to keep INR around 2.5-3.5.
Important Drug and Food Information
From the National Institutes of Health Clinical Center
Drug-Nutrient Interaction Task Force
Important information to know when you are taking: Warfarin (Coumadin) and Vitamin K
The food you eat can affect how your medicine works. It is important to learn about
possible drug-nutrient interactions for any medicines you take.
Why was warfarin (Coumadin) prescribed for you?
Warfarin (Coumadin) is a medicine prescribed for people at increased risk of forming
blood clots. Sometimes medical conditions can make blood clot too easily and quickly.
This could cause serious health problems because clots can block the flow of blood to
the heart or brain. Warfarin (Coumadin) can prevent harmful blood clots from forming.
How does warfarin work?
Blood clots are formed through a series of chemical reactions in your body. Vitamin K is
essential for those reactions. Warfarin (Coumadin) works by decreasing the activity of
vitamin K; lengthening the time it takes for a clot to form.
International Normalized Ratio (INR) and Prothrombin Time (PT) are laboratory test
values obtained from measurements of the time it takes blood to clot. Individuals at
risk for developing blood clots take warfarin (Coumadin) to lengthen the usual time it
takes for a clot to form, resulting in a prolonged INR/PT. Doctors usually measure the
INR/PT every month in patients taking warfarin (Coumadin) to make sure it stays in the
What can help keep INR/PT in the desired range?
To help warfarin (Coumadin) work effectively, it is important to keep your vitamin K
intake as consistent as possible. Sudden increases in vitamin K intake may decrease
the effect of warfarin (Coumadin). On the other hand, greatly lowering your vitamin K
intake could increase the effect of warfarin (Coumadin).
To keep INR/PT stable and within the recommended range, it is important to:
• Take your medicine exactly as your doctor directed.
• Have your INR/PT checked regularly.
• Keep your vitamin K intake consistent from day to day.
How do I keep my vitamin K intake consistent?
• Keep your intake of foods rich in vitamin K about the same each day. For
example, you may plan to eat only ½ cup of these foods per day. If you like
these foods and eat them often, you can eat more, but be consistent.
- Eat no more than 1 serving of food that contains 200%-600% DV of vitamin K
- Eat no more than 3 servings of foods that contain 60-200% DV of vitamin K
- Eliminate alcohol if you can, or limit yourself to no more than 3 drinks a day
- Take no more than 800IU of vitamin E supplements
- Avoid cranberries and cranberry juice as they can raise INR and risk of bleeding
- Limit or avoid grapefruit and grapefruit juice
- Work with your doctor when taking CoQ10 as it can hamper the effectiveness of Warfarin
- Many natural supplements affect PT/INR levels, so it is best to avoid them unless your doctor advises otherwise. The following supplements definitely affect PT/INR levels: arnica, bilberry, butchers broom, cat’s claw, dong quai, feverfew, forskolin, garlic, ginger, gingko, horse chestnut, insositol hexaphosphate, licorice, melilot(sweet clover), pau d’arco, red clover, St. John’s wort, sweet woodruff, turmeric, willow bark, and wheat grass.
- To find foods low in vitamin K, see the article on low vitamin K foods, check the nutrition facts for a particular food, or use the nutrient ranking tool to find low vitamin K foods in a particular food group.