Warfarin Institute of America
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VITAMIN E INTERACTIONS WITH WARFARIN
There is conflicting information about the effect of vitamin E on warfarin. Since vitamin E is an antioxidant, it may inhibit the oxidation of vitamin K. This is one of the steps necessary for your body to have its natural clotting factors. If this is the case, taking vitamin E could lead to bleeding with warfarin because there would two agents decreasing clotting factors.
Corrigan reported on a person who developed bruising and blood in the urine while taking warfarin and 1200 IU of vitamin E daily. The same researches found that neither 100 IU or 400 IU of vitamin E daily had any effect on warfarin.
Yet another study tried 800 IU and 1200 IU of vitamin E on warfarin patients and found no effect. However, the study was small and lasted only one month.
In her review article on this subject, Heck recommends that, "patients receiving warfarin who are beginning vitamin E therapy, particularly doses greater than 400 units/day, should have INR measurements conducted one to two weeks after starting vitamin E. This should be followed by INR monitoring every two to four weeks during the first two months of combination therapy."
The following was written by one of my students
Vitamin E is used therapeutically due to reports it may help prevent atherosclerosis and coronary artery disease (CAD). (1,7) It may also interfere with vitamin K dependent clotting factors, increasing risk of bleeding, particularly in patients on warfarin therapy. (2) Vitamin E may interfere with the oxidation of reduced vitamin K. (3) A case report and two studies are available in the literature. Their conclusions are somewhat conflicting. Therefore close monitoring is advised in patients concurrently taking warfarin and vitamin E.
Case report:
Vitamin E plus warfarin resulted in a hemorrhagic state due to reduction in factors II, VII, IX, and X. Coagulopathy subsided upon discontinuation of vitamin E. (4)
Vitamin E can exacerbate the blood coagulation defect of vitamin K deficiency caused by malabsorption or anticoagulant therapy (5)
Studies:
Double blind,4 week study of 25 patients. (1) None of the patients required warfarin dose adjustments on doses of vitamin E up to 1200 U/day X 1 month. Conclusion: moderate to large doses of vitamin E can be used safely in patients on warfarin.
Double blind, 4 week study in 200 healthy college student volunteers (6) Given 600 IU vitamin E daily. No effect found on prothrombin time.
References:
Kim JM, White RH. Effect of vitamin E on the anticoagulatn response to warfarin. Am J Cardiology 1996; 77: 545-6.
http://www.micromedex.com Complementary and Alternative Medicine AltMedDex, as seen on March 1, 2001.
Corrigan JJ, Ulfers LL. Effect of vitamin E on prothrombin levels in warfarin-induced vitamin K deficieny. Am J Clin Nutr 1981; 34: 1701-5.
Corrigan JJ, Marcus FI. Coagulopathy associated with vitamin E ingestion. JAMA 1974; 230:1300-1.
Kappus H, Diplock AT. Tolerance and safety of vitamin E: a toxicological position report. Free Radical Biology & Medicine 1992; 13: 55-74.
Tsai NC, Kelley JJ, Peng B, Cook N. Study on the effects of megavitamin E supplementation in man. Am J Clin Nutr 1978; 31: 831-7.
Tribble DL, Frank E. Dietary antioxidants, cancer, and atherosclerotic heart disease. WJM 1994; 161: 605-12.
Harris JE. Interactions of dietary factors with oral anticoagulants: review and applications. J Am Dietetic Assoc 1995; 95: 580-5.
Heck et al. Potential interactions between alternative therapies and warfarin. Am J Health-Syst Pharm. 2000;57:1221-1230.
© 2001 Patricia Chuong
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Last updated November 27, 2004