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The safe upper intake level (UL) of vitamin E for adults is set at 1,000 mg daily. 1 The equivalent amounts are 1,500 IU of natural vitamin E and 1,100 IU of synthetic vitamin E. (For technical reasons, the conversion factor is a bit different than in the daily intake recommendations above.) For pregnant women under 19 years of age, the upper limit is 800 mg.
Vitamin E has a blood-thinning effect that could lead to problems in certain situations. In one study of 28,519 men, vitamin E supplementation at the low dose of about 50 IU synthetic vitamin E per day caused an increase in fatal hemorrhagic strokes, the kind of stroke caused by bleeding. 2 However, it reduced the risk of a more common type of stroke, 3 and the two effects essentially canceled out.
Based on its blood-thinning effects, there are concerns that vitamin E could cause problems if it is combined with medications that also thin the blood, such as warfarin (Coumadin), heparin, clopidogrel (Plavix), ticlopidine (Ticlid), pentoxifylline (Trental), and aspirin. Theoretically, the net result could be to thin the blood too much, causing bleeding problems. A study that evaluated vitamin E plus aspirin did in fact find an additive effect. 4 In contrast, the results of a study on vitamin E and Coumadin found no evidence of interaction, but it would still not be advisable to combine these treatments except under a physician's supervision. 5 There is also at least a remote possibility that vitamin E could also interact with supplements that possess a mild blood-thinning effect, such as garlic, policosanol, and ginkgo. Individuals with bleeding disorders such as hemophilia, and those about to undergo surgery or labor and delivery should also approach vitamin E with caution.
In addition, vitamin E might at least temporarily enhance the body's sensitivity to its own insulin in individuals with adult-onset diabetes. 6 This could lead to a risk of blood sugar levels falling too low. In addition, one study found that use of vitamin E can raise blood pressure in people with diabetes. 7 The bottom line: If you have diabetes, do not take high-dose vitamin E without first consulting your physician.
When all major vitamin E studies are statistically combined through a process called “meta-analysis,” some evidence appears suggesting that long-term usage of vitamin E at high doses might increase overall death rate, for reasons that are unclear. 8 The results of one large study involving 29,000 males indicate that vitamin E supplementation may increase risk of tuberculosis in heavy smokers. Curiously, however, this was only true in those participants who also consumed high levels of vitamin C (at least 90 mg/d) in their diet. Consuming high levels of vitamin C without supplemental vitamin E actually led to a reduction in tuberculosis risk. 9 Finally, considerable controversy exists regarding whether it is safe or appropriate to combine vitamin E with standard chemotherapy drugs. 10 The reasoning behind this concern is that some chemotherapy drugs may work in part by creating free radicals that destroy cancer cells. Antioxidants like vitamin E might interfere with this beneficial effect. However, there is no good evidence that antioxidants actually interfere with chemotherapy drugs, growing evidence that they do not, and some evidence of potential benefit under certain circumstances. 11 Nonetheless, in view of the high stakes involved, we strongly recommend that you do not take any supplements while undergoing cancer chemotherapy, except on the advice of a physician.
Interactions You Should Know About
- Seek medical advice before taking vitamin E if you are taking blood thinning drugs, such as:
- Warfarin (Coumadin) , heparin , clopidogrel (Plavix), ticlopidine (Ticlid), pentoxifylline (Trental), or aspirin
- Vitamin E may help protect you from lung-related side effects if you are taking amiodarone.
- Vitamin E may help reduce side effects if you are taking phenothiazine drugs.
- Seek medical advice before taking vitamin E if you are taking chemotherapy drugs.
- High-dose vitamin E might cause your blood sugar levels to fall too low, requiring an adjustment in medication dosage if you are taking oral hypoglycemic medications.
- Dietary reference intakes (DRIs) for vitamins C and E, selenium and carotenoids. National Academies website. Available at: http://www4.nationalacademies.org/IOM/IOMHome.nsf/Pages/Food+and+Nutrition+Board. Accessed January 16, 2001.
- Leppälä JM, Virtamo J, Fogelholm R, Huttunen JK, Albanes D, Taylor PR, Heinonen OP. Controlled trial of alpha-tocopherol and beta-carotene supplements on stroke incidence and mortality in male smokers. Arterioscler Thromb Vasc Biol. 20(1):230-5.
- Leppälä JM, Virtamo J, Fogelholm R, Albanes D, Taylor PR, Heinonen OP. Vitamin E and beta carotene supplementation in high risk for stroke: a subgroup analysis of the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study. Arch Neurol. 57(10):1503-9.
- Liede KE, Haukka JK, Saxén LM, Heinonen OP. Increased tendency towards gingival bleeding caused by joint effect of alpha-tocopherol supplementation and acetylsalicylic acid. Ann Med. 30(6):542-6.
- Kim JM, White RH. Effect of vitamin E on the anticoagulant response to warfarin. Am J Cardiol. 77(7):545-6.
- Paolisso G, D'Amore A, Giugliano D, Ceriello A, Varricchio M, D'Onofrio F. Pharmacologic doses of vitamin E improve insulin action in healthy subjects and non-insulin-dependent diabetic patients. Am J Clin Nutr. 57(5):650-6.
- Ward NC, Hodgson JM, Puddey IB, et al. Vitamin E increases blood pressure in type 2 diabetic subjects, independent of vascular function and oxidative stress. Asia Pac J Clin Nutr. 2005;14(suppl):S41.
- Miller ER 3rd, Pastor-Barriuso R, Dalal D, Riemersma RA, Appel LJ, Guallar E. Meta-analysis: high-dosage vitamin E supplementation may increase all-cause mortality. Ann Intern Med. 142(1):37-46.
- Hemilä H, Kaprio J. Vitamin E supplementation may transiently increase tuberculosis risk in males who smoke heavily and have high dietary vitamin C intake. Br J Nutr. 100(4):896-902.
- Labriola D, Livingston R. Possible interactions between dietary antioxidants and chemotherapy. Oncology. 1999;13:1003-1012.
- Weijl NI, Cleton FJ, Osanto S. Free radicals and antioxidants in chemotherapy-induced toxicity. Cancer Treat Rev. 23(4):209-40.
- Bairati I, Meyer F, Gélinas M, Fortin A, Nabid A, Brochet F, Mercier JP, Têtu B, Harel F, Mâsse B, Vigneault E, Vass S, del Vecchio P, Roy J. A randomized trial of antioxidant vitamins to prevent second primary cancers in head and neck cancer patients. J Natl Cancer Inst. 97(7):481-8.