Vitamin E Toxicity
Vitamin E is a group of compounds (including tocopherols and tocotrienols) that have similar biologic activities. The most biologically active is alpha-tocopherol, but beta-, gamma-, and delta-tocopherols, 4 tocotrienols, and several stereoisomers may also have important biologic activity. These compounds act as antioxidants, which prevent lipid peroxidation of polyunsaturated fatty acids in cellular membranes (see table Sources, Functions, and Effects of Vitamins). Dietary sources of vitamin E include vegetable oils and nuts.
Plasma tocopherol levels vary with total plasma lipid levels. Normally, the plasma alpha-tocopherol level is 5 to 20 mcg/mL (11.6 to 46.4 mcmol/L).
High-dose vitamin E supplements do not protect against cardiovascular disorders; whether supplements can protect against tardive dyskinesia is controversial. There is no convincing evidence that doses of up to 2000 units/day slow the progression of Alzheimer disease or decrease the risk of prostate cancer; one study suggested an increased risk of prostate cancer with vitamin E supplementation (1).
Although the amount of vitamin E in many fortified foods and supplements is given in units, current recommendations are to use mg.
(See also Overview of Vitamins.)
Many adults take relatively large amounts of vitamin E (alpha-tocopherol 400 to 800 mg/day) for months to years without any apparent harm. Occasionally, muscle weakness, fatigue, nausea, and diarrhea occur. The most significant risk is bleeding. However, bleeding is uncommon unless the dose is > 1000 mg/day or the patient takes oral coumarin or warfarin. Thus, the upper limit for adults aged ≥ 19 years is 1000 mg for any form of tocopherol.
Analyses of previous studies report that high supplemental vitamin E intake may increase the risk of hemorrhagic stroke and premature death.
1. Klein EA, Thompson IM Jr, Tangen CM, et al: Vitamin E and the risk of prostate cancer: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA 306(14):1549-56, 2011. doi: 10.1001/jama.2011.1437.