Warfarin Institute of America
DEDICATED TO YOUR HEALTH SINCE 2000
FOOD INTERACTIONS WITH WARFARIN
WHEN MOST PEOPLE HEAR THAT A FOOD IS HIGH IN VITAMIN K, THEY IMMEDIATELY JUMP TO THE CONCLUSION THAT THEY CANNOT EAT THAT FOOD IF THEY ARE TAKING WARFARIN. PLEASE DO NOT MAKE THAT MISTAKE. READ THIS SECTION CAREFULLY BEFORE MAKING YOUR FINAL JUDGMENT.
Vitamin K and warfarin can be thought of a sitting on opposite sides of a teeter totter. What you do to one side will affect the other side. However, this does not mean that you cannot bring things back into balance.
Foods that are high in Vitamin K include asparagus, leaf lettuce, broccoli, cabbage and others. What a person taking warfarin needs to do is avoid making large changes in the consumption of these foods. If you routinely eat large amounts of these and start taking warfarin, you will need a higher dose of warfarin than if you did not eat as much of the high vitamin K foods. Remember, it is not the dose of warfarin that you take that is important, it is your INR.
Almost everyone will go out to a dinner and occasionally eat much more vegetables that they normally consume. This will cause the INR to decrease (increase your risk of getting a blood clot) in about 36 to 72 hours. Is this important? It could be, but in most cases, you will, "get away with it". This is because you will return to your normal amount of vegetable consumption after this one meal and your INR will not be down for very long.
Where the major risk occurs is when a person taking warfarin decides to go on a diet and increase their eating of salads. This tends to decrease the INR for longer periods of time and puts them at significant risk of developing a blood clot. If you are going to switch to this type of diet, discuss it with the person monitoring your warfarin. so that your INR can be checked and the warfarin dose adjusted accordingly.
Another source of vitamin K which is frequently overlooked are the supplements such as Carnation Instant Breakfast, Ensure and Boost. These contain significant amounts of vitamin K. The TV advertising does not adequately warn the consumer of this. Physicians often overlook this also. When I see a thin, elderly lady whose INR is suddenly low, the reason she often gives is that her doctor told her to start taking one of these supplements. It is usually necessary to increase the warfarin dose after these products are started.
Many people do not consider taking vitamins as taking "drugs". They start and stop without much thought. If they lack energy, they start vitamins. If they lack money, they stop vitamins. This probably the single largest reason why people cannot get their warfarin dose regulated. They do not consider these items to be important. However, they are very important. Taking vitamins on an occasional basis will cause the INR to fluctuate so that the warfarin dose cannot be regulated.
What about the opposite, decreasing your intake of vitamin K. This usually happens when someone becomes ill and cannot eat. If you are unable to eat your normal amount of vegetables for two or three days, your INR will begin to increase (increase your risk of bleeding). It is important that you have your INR checked and your warfarin dose adjusted if this happens. This is hard to do because you are feeling so bad that you do not want to go out of the house, but it can be important. Stomach flu and cancer chemotherapy are two of the reasons that this happens.
People also use "fruitsandvegetables" as if they were one and the same. You will notice that when I listed foods that were high in vitamin K, there were no fruits listed. Whenever, I asking someone about changes in their eating patterns and they say, " I haven't been eating many vegetables, BUT, I have been eating a lot of fruit," I know that their INR is most likely high. You need to consider fruits and vegetables as two separate things as far as warfarin is concerned.
The dried leaves of green tea contain a large amount of vitamin K. Unless you eat the leaves, as they do in some cultures, this is usually not a cause for concern. Brewing tea results in only a small amount of vitamin K in each serving. There has been at least one case reported where a person lowered their INR by drinking about 1/2 to 1 gallon of green tea daily for about one week.
For a good review of the green tea issue see Heck AM, et al. Potential Interactions Between Alternative Therapies and Warfarin. Am J Health-Syst Pharm. 2000;57:1221-30.
I had one patient who had been consistently having INRs in the 2.5 to 3.0 range. One day she decided that she was hungry for some cole slaw. She went to the store and purchased a large bag of cole slaw mix and dressing. She consumed the entire mixture over about 24 hours. Two days later, her INR was 1.6. Whe I asked her if she were going to continue to eat that amount of cabbage, she replied that she was not. She just wanted some cole slaw and since she lived alone, there was nobody to share it with. When she returned to her normal eating habits, the INR went back into the same range. Had I decided to raise her warfarin dose, her INR would have been too high.
I was able to find a case of a man who ate between one and two pounds of carrots daily as an alternative to smoking. Carrots are medium in their vitamin K content. But he ate so many that it became a major source for him. When he went on a trip which involved an airline flight, he stopped eating the carrots. A few days later his INR was 4.7, and he went to an emergency department for a bloody nose. When he returned home, he resumed his carrot intake and his INR was again well maintained on warfarin 12.5 mg per day. Reference: Beanland DR. Monitoring Warfarin Therapy (letter). Am Fam Phys 1999;60:764.
If you would like information about vitamin K in foods call 1-800 COUMADIN OR 1-888 WARFARIN.
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Last updated April 5, 2007