Vitamin E is a group of eight fat soluble compounds that include four tocopherols and four tocotrienols. Vitamin E deficiency, which is rare and usually due to an underlying problem with digesting dietary fat rather than from a diet low in vitamin E, can cause nerve problems. The crucial function played by Vitamin E that makes it a vitamin is poorly understood, but may involve antioxidant functions in cell membranes. Other theories hold that vitamin E–specifically the RRR stereoisomer of alpha-tocopherol–act by controlling gene expression and cell signal transduction.
Worldwide, government organizations recommend adults consume in the range of 7 to 15 mg per day. As of 2016, consumption was below recommendations according to a worldwide summary of more than one hundred studies that reported a median dietary intake of 6.2 mg per day for alpha-tocopherol. Research with alpha-tocopherol as a dietary supplement, with daily amounts as high as 2000 mg per day, has had mixed results. Population studies suggested that people who consumed foods with more vitamin E, or who chose on their own to consume a vitamin E dietary supplement, had lower incidence of cardiovascular diseases, cancer, dementia, and other diseases, but placebo-controlled clinical trials could not always replicate these findings, and there were some indications that vitamin E supplementation actually was associated with a modest increase in all-cause mortality.As of 2017, vitamin E continues to be a topic of active clinical research.Although people commonly apply Vitamin E oil to their skin to try to improve wound healing and reduce scar tissue, reviews have repeatedly concluded that there is no good evidence that this is helpful.
Both the tocopherols and tocotrienols occur in α (alpha), β (beta), γ (gamma) and δ (delta) forms, as determined by the number and position of methyl groups on the chromanol ring. All eight of these vitamers feature a chromane double ring, with a hydroxyl group that can donate a hydrogen atom to reduce free radicals, and a hydrophobic side chain which allows for penetration into biological membranes. Of the many different forms of vitamin E, gamma-tocopherol (γ-tocopherol) is the most common form found in the North American diet, but alpha-tocopherol (α-tocopherol) is the most biologically active. Palm oil is a source of tocotrienols.
Vitamin E was discovered in 1922, isolated in 1935 and first synthesized in 1938. Because the vitamin activity was first identified as essential for fertilized eggs to result in live births (in rats), it was given the name "tocopherol" from Greek words meaning birth and to bear or carry.Alpha-tocopherol, either naturally extracted from plant oils or synthetic, is sold as a popular dietary supplement, either by itself or incorporated into a multivitamin product, and in oils or lotions for use on skin.