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Vitamin E is a fat-soluble organic compound that the body needs to remain healthy. Humans cannot make vitamin E, so they must get it from foods in their diet. Vitamin E comes in eight forms. The most biologically active form in humans is alpha-toco-pherol. Most vitamin E in dietary supplements is synthetically manufactured alpha-tocopherol.
Vitamin E is one of the more poorly understood and controversial vitamins. Its exact functions are not completely clear. Vitamin E is an antioxidant. Antioxidants help protect the body against damage caused by free radicals. Free radicals are formed during normal metabolic processes. The quantity of free radicals in the body may also be increased by exposure to environmental toxins, ultraviolet light, and radiation. Free radicals have a strong tendency to react with and damage other compounds, especially those in DNA (genetic material) and certain fats (lipids) in cell membranes. Antioxidants prevent this damage by reacting with free radicals to neutralneutralize
(Illustration by GGS Information Services/Thomson Gale.)
them. The damage that free radicals cause to cells is believed to play a role in the development of certain diseases, especially cancer. Many of the health claims for vitamin E are based on its antioxidant properties.
Vitamin E is a collection of eight different, but closely related, compounds. These are alpha-, beta-, gamma-, and delta-tocopherol and alpha-, beta-, gamma-, and delta-tocotrienol. Each of these compounds has a different degree of activity in humans. Alpha-tocopherol is the most active form. Vitamin E in dietary supplements is usually a synthetic compound called alpha-tocopherol acetate. Synthetic alpha-tocopherol is sometimes labeled dl-alpha-tocopherol.
Normal vitamin E requirements
The IOM has not set RDA or UL values for vitamin E in children under one year old because of incomplete scientific information. Instead, it has set AI levels for this age group. Recently the UL level has become somewhat controversial and has been challenged by some researchers as being set too high. AI and UL levels are measured in both weight (milligrams or mg) and international units (IU). The IU measurement is the measurement used on dietary supplement labels. For the alpha-tocopherol form of vitamin E, 1 mg equals about 1.5 IU.
The following are the AIs, RDAs, and ULs for alpha-tocopherol for healthy individuals:
Sources of vitamin E
Vitamin E is found in limited amounts in a small number of foods. These include some oils, nuts, and green leafy vegetables. Vitamin E is also added to some breakfast cereals, which say“fortified with vitamin E” on the label. In addition, the Food and Drug Administration requires all foods containing olestra, a compound that reduces fat absorption, to be fortified with the fat-soluble vitamins A, D, E, and K.
The following list gives the approximate vitamin E (alpha-tocopherol) content for some common foods:
Vitamin E's role in health
Almost all healthy people living in the developed world get enough vitamin E through diet to prevent symptoms of vitamin E deficiency from developing. There is some debate, however, about the frequency with which deficiencies exist that do not produce obvious symptoms (subclinical deficiencies). Those at greatest risk for vitamin E deficiency include:
Controversy about vitamin E centers on its use as a dietary supplement to help prevent or treat disease. Many health claims are based on the antioxidant properties of vitamin E. Initially, it appeared that large doses of vitamin E could help prevent heart disease and some cancers. Then in 2004, researchers at the Johns Hopkins University School of Medicine re-analyzed the data (a meta-analysis) from 19 major clinical trials that included more than 136,000 individuals. They found that taking 400IU or more of vitamin E daily increased a person's risk of death by about 4%. However, some experts have questioned the validity of the Johns Hopkins analysis. The role of vitamin E is further complicated by the fact that it comes in many forms, and researchers are not completely clear on what, if any, roles the different forms play in maintaining human health. Clinical trials are currently underway to determine safety and effectiveness of vitamin E in a variety of situations. Individuals interested in participating in a clinical trial at no charge can find a list of open trials http://www.clinicaltrials.gov.
CARDIOVASCULAR DISEASE. Since the 1940s, researchers have suggested that vitamin E might protect against heart disease. This theory is based on its activity as an antioxidant. Because vitamin E oxidizes (neutralizes) LDL or“bad” cholesterol, researchers have suggested that large doses of vitamin E may slow or prevent the build-up of material on the wall of arteries and thus help prevent cardiovascular disease.
Results of studies testing this idea are mixed. Several large studies followed healthy people who took vitamin E and looked for a correlation between the amount of vitamin E in their diet and whether they were diagnosed with heart disease or died of a heart attack. Two studies found that people who got least 7 mg of alpha-tocopherol daily from food were about one-third less likely to die from heart disease than those people who consumed 5 mg of less of alpha-tocopherol. On the other hand, another large, well-designed study (the Heart Outcomes Prevention Evaluation) found no cardiovascular benefit to large doses of vitamin E. A well-controlled study (the CHAOS study) done in Great Britain found that when people who already had heart disease were given large doses (400 IU or 800 IU) of Vitamin E, the rate of non-fatal heart attacks dropped dramatically, but that the overall death rate from heart disease did not change.
The official position of the American Heart Association published in its“Diet and Lifestyle Recommendations Revision 2006” is that“Antioxidant supplements have not been shown to be helpful in preventing heart disease and are not recommended in these guidelines.” The recommendations specifically mention the possibility of“an increased risk of heart failure and the possibility of increased total mortality (death) from high dose vitamin E supplements.” More research needs to be done in this area.
CANCER. The antioxidant activities of vitamin E are also thought to help protect against the development of cancer by removing free radicals that damage cell membranes and DNA. Vitamin E is also believed to neutralize nitrosamines. Nitrosamines are known carcinogens found in tobacco and smoked meats. Much of the evidence for the action of vitamin E on cancer comes from animal studies. The results of human studies are inconclusive and often confusing. According to the American Cancer Society, there is some evidence that vitamin E may have a protective effect against coon, rectal, bladder, and prostate cancer, but not other cancers. There is no evidence that vitamin E slows the growth of cancer once it has already developed, and some conflicting evidence about whether it interferes with the effectiveness of chemotherapy and radiation therapy. Research on the relationship of vitamin E and cancer continues.
There is a great deal of debate about how much vitamin E is too much. The UL for healthy adults in the United States is 1,500 IU daily. However, some experts feel this is too high, especially since it is based on research done in the 1950s. They argue that UL should be lower since the Johns Hopkins study found that daily amounts over 400 IU increased the death rate and protective effects of larger doses of vitamin E are still unproven. In the United Kingdom, the recommended daily limit of vitamin E is 800 UI.
Large doses of vitamin E increase the chance of bleeding. People who are taking blood-thinning medications such as warfarin (Coumadin), heparin, and clopidogrel (Plavix) should discuss the use of vitamin E with their healthcare providers. Other people who should be wary of taking vitamin E as a dietary supplement are those who are vitamin K deficient, who have liver damage, and those with a history of bleeding ulcers. Vitamin E supplementation should be stopped about one month before surgery because of the increased risk of bleeding. Other possible, but uncommon, side effects of vitamin E supplementation include nausea, vomiting, diarrhea, damage to the retina, breast soreness, fatigue, emotional disturbances, and thyroid hormone disturbances.
Vitamin E may interact with the following:
No complications are expected when vitamin E is used in the recommended amounts. The complications resulting from insufficient or excess use are discussed above.
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Office of Dietary Supplements, National Institutes of Health. 6100 Executive Blvd., Room 3B01, MSC 7517, Bethesda, MD 20892-7517 Telephone: (301)435-2920. Fax: (301)480-1845. Website: <http://dietary-supplements.info.nih.gov/>
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Tish Davidson, A.M.