The adult safe upper intake level (UL) for 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 Lineline: 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.
One study appeared to find evidence that use of vitamin E plus beta-carotene may impair the effectiveness of radiation therapy for head and neck cancers. 12
