RDAs for vitamin E are provided in milligrams (mg) and are listed in Table 1. Naturally sourced vitamin E is called RRR-alpha-tocopherol (commonly labeled as d-alpha-tocopherol) the synthetically produced form is all rac-alpha-tocopherol (commonly labeled as dl-alpha-tocopherol). Acknowledging "great uncertainties" in these data, the FNB has called for research to identify other biomarkers for assessing vitamin E requirements. The FNB based these recommendations primarily on serum levels of the nutrient that provide adequate protection in a test measuring the survival of erythrocytes when exposed to hydrogen peroxide, a free radical. The FNB's vitamin E recommendations are for alpha-tocopherol alone, the only form maintained in plasma. Tolerable Upper Intake Level (UL): Maximum daily intake unlikely to cause adverse health effects.Estimated Average Requirement (EAR): Average daily level of intake estimated to meet the requirements of 50% of healthy individuals usually used to assess the nutrient intakes of groups of people and to plan nutritionally adequate diets for them can also be used to assess the nutrient intakes of individuals.Adequate Intake (AI): Intake at this level is assumed to ensure nutritional adequacy established when evidence is insufficient to develop an RDA.Recommended Dietary Allowance (RDA): Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals often used to plan nutritionally adequate diets for individuals.These values, which vary by age and gender, include: DRI is the general term for a set of reference values used to plan and assess nutrient intakes of healthy people. Intake recommendations for vitamin E and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine of The National Academies (formerly National Academy of Sciences). Vitamin E also increases the expression of two enzymes that suppress arachidonic acid metabolism, thereby increasing the release of prostacyclin from the endothelium, which, in turn, dilates blood vessels and inhibits platelet aggregation. Vitamin-E–replete endothelial cells lining the interior surface of blood vessels are better able to resist blood-cell components adhering to this surface. Alpha-tocopherol inhibits the activity of protein kinase C, an enzyme involved in cell proliferation and differentiation in smooth muscle cells, platelets, and monocytes. In addition to its activities as an antioxidant, vitamin E is involved in immune function and, as shown primarily by in vitro studies of cells, cell signaling, regulation of gene expression, and other metabolic processes. Scientists are investigating whether, by limiting free-radical production and possibly through other mechanisms, vitamin E might help prevent or delay the chronic diseases associated with free radicals. Vitamin E is a fat-soluble antioxidant that stops the production of ROS formed when fat undergoes oxidation. ROS are part of signaling mechanisms among cells. The body is also exposed to free radicals from environmental exposures, such as cigarette smoke, air pollution, and ultraviolet radiation from the sun. The body forms ROS endogenously when it converts food to energy, and antioxidants might protect cells from the damaging effects of ROS. Unshared electrons are highly energetic and react rapidly with oxygen to form reactive oxygen species (ROS). Free radicals damage cells and might contribute to the development of cardiovascular disease and cancer. Īntioxidants protect cells from the damaging effects of free radicals, which are molecules that contain an unshared electron. As a result, blood and cellular concentrations of other forms of vitamin E are lower than those of alpha-tocopherol and have been the subjects of less research. The liver preferentially resecretes only alpha-tocopherol via the hepatic alpha-tocopherol transfer protein the liver metabolizes and excretes the other vitamin E forms. Serum concentrations of vitamin E (alpha-tocopherol) depend on the liver, which takes up the nutrient after the various forms are absorbed from the small intestine. Alpha- (or α-) tocopherol is the only form that is recognized to meet human requirements. Naturally occurring vitamin E exists in eight chemical forms (alpha-, beta-, gamma-, and delta-tocopherol and alpha-, beta-, gamma-, and delta-tocotrienol) that have varying levels of biological activity. "Vitamin E" is the collective name for a group of fat-soluble compounds with distinctive antioxidant activities. Vitamin E is found naturally in some foods, added to others, and available as a dietary supplement. For a reader-friendly overview of Vitamin E, see our consumer fact sheet on Vitamin E. This is a fact sheet intended for health professionals.
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