Vitamin E is a fat-soluble antioxidant that stops the production of reactive oxygen species formed when fat undergoes oxidation. Vitamin E is an antioxidant that protects body tissue from damage caused by unstable substances called free radicals. Free radicals can harm cells, tissues, and organs. They are believed to play a role in certain conditions associated with aging.
Vitamin E is found naturally in some foods, added to others, and available as a dietary supplement. "Vitamin E" is the collective name for a group of fat-soluble compounds with distinctive antioxidant activities 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. Alpha-tocopherol is the only form that is recognized to meet human requirements.
It has been claimed that A-tocopherol is the most important lipid-soluble antioxidant, and that it protects cell membranes from oxidation by reacting with lipid radicals produced in the lipid peroxidation chain reaction. This would remove the free radical intermediates and prevent the oxidation reaction from continuing. The oxidised A-tocopheroxyl radicals produced in this process may be recycled back to the active reduced form through reduction by other antioxidants, such as ascorbate, retinol or ubiquinol. However, the importance of the antioxidant properties of this molecule at the concentrations present in the body are not clear and it is possible that the reason why Vitamin E is required in the diet is unrelated to its ability to act as an antioxidant.. Other forms of Vitamin E have their own unique properties. For example, Y-tocopherol (also written as gamma-tocopherol) is a nucleophile that can react with electrophilic mutagens.
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. The liver preferentially resecretes only alpha-tocopherol via the hepatic alpha-tocopherol transfer protein; the liver metabolizes and excretes the other Vitamin E forms. 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. However, the roles and importance of all of the various forms of Vitamin E are presently unclear, and it has even been suggested that the most important function of Vitamin E is as a signaling molecule, and that it has no significant role in antioxidant metabolism.
Antioxidants protect cells from the damaging effects of free radicals, which are molecules that contain an unshared electron. Free radicals damage cells and might contribute to the development of cardiovascular disease and cancer. Unshared electrons are highly energetic and react rapidly with oxygen to form reactive oxygen species (ROS). The body forms ROS endogenously when it converts food to energy, and antioxidants might protect cells from the damaging effects of ROS. The body is also exposed to free radicals from environmental exposures, such as cigarette smoke, air pollution, and ultraviolet radiation from the sun. ROS are part of signaling mechanisms among cells. Vitamin E is a fat-soluble antioxidant that stops the production of ROS formed when fat undergoes oxidation. 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 also important in the formation of red blood cells and helps the body to use Vitamin K.
The ability of Vitamin E to prevent cancer, heart disease, dementia, liver disease, and stroke are still not known. At lower levels, Vitamin E may help protect the heart.
The best way to get enough essential Vitamins is to eat a balanced diet that contains a variety of foods.
The Food and Nutrition Board at the Institute of Medicine report the following dietary reference intakes for Vitamin E.
- Recommended Dietary Allowance (RDA): average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%-98%) healthy people.
- Adequate Intake (AI): established when evidence is insufficient to develop an RDA and is set at a level assumed to ensure nutritional adequacy.
- Tolerable Upper Intake Level (UL): maximum daily intake unlikely to cause adverse health effects.
- 0 to 6 months: 4 mg/day
- 7 to 12 months: 5 mg/day
- 1 to 3 years: 6 mg/day
- 4 to 8 years: 7 mg/day
- 9 to 13 years: 11 mg/day
Adolescents and Adults
The best way to get the daily requirement of essential Vitamins is to eat a balanced diet that contains a variety of foods. Specific recommendations depend on age, gender, and other factors (such as pregnancy). Women who are pregnant or producing breast milk (lactating) need higher amounts. Ask your health care provider which amount is best for you.
Numerous foods provide Vitamin E. Nuts, seeds, and vegetable oils are among the best sources of alpha-tocopherol, and significant amounts are available in green leafy vegetables and fortified cereals. Vitamin E is found in the following foods:
Spinach and other green leafy vegetables
Vegetable oils, corn, sunflower, soybean, cottonseed.
Vitamin E deficiency is rare and overt deficiency symptoms have not been found in healthy people who obtain little Vitamin E from their diets. Premature babies of very low birth weight (<1,500 grams) might be deficient in Vitamin E. Vitamin E supplementation in these infants might reduce the risk of some complications, such as those affecting the retina, but they can also increase the risk of infections.
Because the digestive tract requires fat to absorb Vitamin E, people with fat-malabsorption disorders are more likely to become deficient than people without such disorders. Deficiency symptoms include peripheral neuropathy, ataxia, skeletal myopathy, retinopathy, and impairment of the immune response. People with Crohn's disease, cystic fibrosis, or an inability to secrete bile from the liver into the digestive tract, for example, often pass greasy stools or have chronic diarrhea; as a result, they sometimes require water-soluble forms of Vitamin E, such as tocopheryl polyethylene glycol-1000 succinate.
In November, 2004, the American Heart Association stated that high amounts of Vitamin E can be harmful. Taking 400 IU per day, or higher, may increase the risk of death.
Taking smaller amounts, such as those found in a typical multi-Vitamins, was not harmful.
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