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Warfarin Food Interactions

Warfarin is a medication that is used to make your blood thinner preventing the formation of clots. Some disease conditions such as atrial fibrillation, deep vein thrombosis and anti-phospholipid syndrome can make you more prone to get blood clots. Warfarin acts by inhibiting the synthesis of vitamin K dependent clotting factors namely II, VII, IX and X along with regulatory proteins C, S and Z.
Warfarin is a drug that has many interactions with food. Since dosing of warfarin has to be monitored closely to maintain a specific INR in your blood, you need to pay close attention to the components in your diet. Intake of food rich in vitamin K can reduce the efficacy of warfarin. Although small intakes won’t matter, sudden changes in the diet including vitamin K rich food can pose a problem. The main source of vitamin K is found in dark green vegetables such as kale, spinach, parseley, Brussels sprouts, chard, broccoli, escarole and cabbage. The United States Department of Agriculture revised the food pyramid in 2005 to include food rich in vitamin K such as green vegetables, dry beans and peas, starchy vegetables and other vegetables and included guidelines on the average requirements that should be taken according to age. Exceeding that amount will result in problems.  
Oils such as rapseed, soybean and olive are not only rich sources of vitamin K; it can also increase the absorption of vitamin K in food. However heating the oil for 20minutes can decrease the vitamin K content by 7%. Oil in processed and fast food is something that is often overlooked but poses a significant problem when consumed in large amounts. These include olestra tortilla chips, cheeto-type chips, potato chips, chicken sandwich and French fries. Although fruits are not great sources of vitamin K, there are reports about interactions with avocado when consumed daily.  
Action of warfarin can also be potentiated by some food sources leading to bleeding tendency.  Alcohol and grape fruit juice can decrease warfarin metabolism enhancing its action. Cranberry juice, garlic, ginger have antiplatelet effects which can increase bleeding risk when taking warfarin. Vitamin A in mango can inhibit enzymes metabolizing warfarin leading to increased INR. Papaya is also shown to increase bleeding risk with warfarin in unknown mechanisms.
Green tea has conflicting reports. It can decrease the effect of warfarin since it contains vitamin K and it can also increase the effects of warfarin by being an antiplatelet agent. There have been reports supporting the both effects therefore green tea also should be consumed with caution.


Nutescu, E., Shapiro, N., Ibrahim, S., & West, P. (2006). Warfarin and its interactions with foods, herbs and other dietary supplements. Expert Opinion On Drug Safety, 5(3), 433-451.
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