Vitamin E

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. Vitamin E is a fat-soluble antioxidant protecting cell membranes from reactive oxygen species. 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. Vitamin E is a fat-soluble antioxidant protecting cell membranes from reactive oxygen species. 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. There is no clinical evidence that use of vitamin E skincare products are effective. 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. Vitamin E may have various roles as a vitamin. Many biological functions have been postulated, including a role as a fat-soluble antioxidant. In this role, vitamin E acts as a radical scavenger, delivering a hydrogen (H) atom to free radicals. At 323 kJ/mol, the O-H bond in tocopherols is about 10% weaker than in most other phenols. This weak bond allows the vitamin to donate a hydrogen atom to the peroxyl radical and other free radicals, minimizing their damaging effect. The thus-generated tocopheryl radical is recycled to tocopherol by a redox reaction with a hydrogen donor, such as vitamin C. As it is fat-soluble, vitamin E is incorporated into cell membranes, which are therefore protected from oxidative damage. Vitamin E affects gene expression and is an enzyme activity regulator, such as for protein kinase C (PKC) – which plays a role in smooth muscle growth – with vitamin E participating in deactivation of PKC to inhibit smooth muscle growth. Vitamin E deficiency is rare in humans, occurring as a consequence of abnormalities in dietary fat absorption or metabolism rather than from a diet low in vitamin E. One example of a genetic abnormality in metabolism is mutations of genes coding for alpha-tocopherol transfer protein (α-TTP). Humans with this genetic defect exhibit a progressive neurodegenerative disorder known as ataxia with vitamin E deficiency (AVED) despite consuming normal amounts of vitamin E. Large amounts of alpha-tocopherol as a dietary supplement are needed to compensate for the lack of α-TTP Vitamin E deficiency due to either malabsorption or metabolic anomaly can cause nerve problems due to poor conduction of electrical impulses along nerves due to changes in nerve membrane structure and function. In addition to ataxia, vitamin E deficiency can cause peripheral neuropathy, myopathies, retinopathy and impairment of immune responses. In the United States vitamin E supplement use by female health professionals was 16.1% in 1986, 46.2% in 1998, 44.3% in 2002, but decreased to 19.8% in 2006. Similarly, for male health professionals, rates for same years were 18.9%, 52.0%, 49.4% and 24.5%. The authors theorized that declining use in these populations may have been due to publications of studies that showed either no benefits or negative consequences from vitamin E supplements. Within the US military services, vitamin prescriptions written for active, reserve and retired military, and their dependents, were tracked over years 2007-2011. Vitamin E prescriptions decreased by 53% while vitamin C remained constant and vitamin D increased by 454%. A report on vitamin E sales volume in the US documented a 50% decrease between 2000 and 2006, with a potential reason being a meta-analysis that concluded high-dosage vitamin E was associated with an increase in all-cause mortality. The U.S. Food and Nutrition Board set a Tolerable upper intake level (UL) at 1,000 mg (1,500 IU) per day derived from animal models that demonstrated bleeding at high doses. The European Food Safety Authority reviewed the same safety question and set a UL at 300 mg/day. A meta-analysis of long-term clinical trials reported a non-significant 2% increase in all-cause mortality when alpha-tocopherol was the only supplement used. The same meta-analysis reported a statistically significant 3% increase for results when alpha-tocopherol was used by itself or in combination with other nutrients (vitamin A, vitamin C, beta-carotene, selenium). Another meta-analysis reported a non-significant 1% increase in all-cause mortality when alpha-tocopherol was the only supplement. Subset analysis reported no difference between natural (plant extracted) or synthetic alpha-tocopherol, or whether the amount used was less than or more than 400 IU/day. There are reports of vitamin E-induced allergic contact dermatitis from use of vitamin-E derivatives such as tocopheryl linoleate and tocopherol acetate in skin care products. Incidence is low despite widespread use.