Relatively large amounts of vitamin E usually cause no harm, but occasionally muscle weakness, fatigue, nausea, and diarrhea occur. The most significant risk is bleeding, mainly with doses > 1000 mg a day.
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 cancer or cardiovascular disorders, and the US Preventive Services Task Force recommends against taking vitamin E for such reasons (1); whether supplements can protect against tardive dyskinesia is controversial. There is no convincing evidence that doses of natural vitamin E up to 2000 international units/day (1340 mg alpha-tocopherol/day) slow the progression of Alzheimer disease or decrease the risk of cancer; one study suggested an increased risk of prostate cancer with vitamin E supplementation (2). It is uncertain whether vitamin E supplementation affects stroke risk (3).
Although the amount of vitamin E in many fortified foods and supplements is given in units, current recommendations are to use milligrams alpha-tocopherol.
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.
Vitamin E toxicity is treated by stopping the vitamin or reducing intake to less than the upper limit of 1000 mg per day.
(See also Overview of Vitamins.)
Довідкові матеріали
1. Moyer VA; U.S. Preventive Services Task Force. Vitamin, mineral, and multivitamin supplements for the primary prevention of cardiovascular disease and cancer: U.S. Preventive services Task Force recommendation statement. Ann Intern Med. 2014;160(8):558-564. doi:10.7326/M14-0198
2. 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
3. Loh HC, Lim R, Lee KW, et al. Effects of vitamin E on stroke: a systematic review with meta-analysis and trial sequential analysis. Stroke Vasc Neurol. 2021;6(1):109-120. doi:10.1136/svn-2020-000519
