Vitamin E - Alpha Tocopherol

Introducing Vitamin E - The Excellent Antioxidant

Vitamin E is a fat-soluble vitamin that exists in eight different forms - four tocopherols, alpha, beta, gamma and delta, and four tocotrienols (also alpha, beta, gamma, and delta). Each form has its own biological activity, the measure of potency or functional use in the body. Alpha Tocopherol is the only form of vitamin E that is actively maintained in the human body and is therefore, the form of vitamin E found in the largest quantities in the blood and tissue. Because a-tocopherol is the form of vitamin E that appears to have the greatest nutritional significance, therefore it is the element which people use to identify vitamin E. Alpha-tocopherol is a powerful biological antioxidant. Antioxidants such as vitamin E act to protect your cells against the effects of free radicals, which are potentially damaging by-products of the body's metabolism. Free radicals can cause cell damage that may contribute to the development of cardiovascular disease and cancer. Studies are underway to determine whether vitamin E might help prevent or delay the development of those chronic diseases.

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Why Vitamin E?

Alpha-tocopherol (a-tocopherol): The main function of a-tocopherol in humans appears to be that of an antioxidant. Free radicals are formed primarily in the body during normal metabolism and also upon exposure to environmental factors such as cigarette smoke or pollutants. Fats, which are an integral part of all cell membranes, are vulnerable to destruction through oxidation by free radicals. The fat-soluble vitamin, a-tocopherol, is uniquely suited to intercepting free radicals and preventing a chain reaction of lipid destruction. Aside from maintaining the integrity of cell membranes throughout the body, a-tocopherol also protects the fats in low density lipoproteins (LDLs) from oxidation. Lipoproteins are particles composed of lipids and proteins, which are able to transport fats through the blood stream. LDL transport cholesterol from the liver to the tissues of the body. Oxidized LDLs have been implicated in the development of cardiovascular diseases (See Disease Prevention). When a molecule of a-tocopherol neutralizes a free radical, it is altered in such a way that its antioxidant capacity is lost. However, other antioxidants, such as vitamin C, are capable of regenerating the antioxidant capacity of a-tocopherol.

Several other functions of a-tocopherol have been identified, which likely are not related to its antioxidant capacity. a-Tocopherol is known to inhibit the activity of protein kinase C, an important cell signaling molecule, as well as to affect the expression and activity of immune and inflammatory cells. Additionally, a-tocopherol has been shown to inhibit platelet aggregation and to enhance vasodilation.

Gamma-tocopherol (g-tocopherol): The function of g-tocopherol in humans is presently unclear. Although the most common form of vitamin E in the American diet is g-tocopherol (see Food Sources), blood levels of g-tocopherol are generally ten times lower than those of a-tocopherol. This phenomenon appears due to the action of the a-tocopherol transfer protein (a-TTP) in the liver, which preferentially incorporates a-tocopherol into lipoproteins that are circulated in the blood and ultimately delivers a-tocopherol to different tissues in the body. See the Linus Pauling Institute Newsletter for more information about a-TTP and vitamin E adequacy. Because g-tocopherol is initially absorbed in the same manner as a-tocopherol, small amounts are detectable in blood and tissue. Products of the metabolism of tocopherols, known as metabolites, can be detected in the urine. More g-tocopherol metabolites are excreted in the urine than a-tocopherol metabolites, suggesting less g-tocopherol is needed for use by the body. Limited research in the test tube and in animals indicates that g-tocopherol or its metabolites may play a role in the protection of the body from damage by free radicals, but these effects have not been convincingly demonstrated in humans. Recently, concern has been raised regarding the fact that taking a-tocopherol supplements lowers g-tocopherol levels in the blood. However, no adverse effects of moderate a-tocopherol supplementation have been demonstrated, while many benefits have been documented (see Disease Prevention and Disease Treatment). In one recent prospective study, increased plasma g-tocopherol levels were associated with a significantly reduced risk of developing prostate cancer, while significant protective associations for increased levels of plasma a-tocopherol and toenail selenium were found only when g-tocopherol levels were also high. These limited findings, in addition to the fact that taking a-tocopherol supplements lower g-tocopherol levels in the blood, have led some scientists to call for additional research on the effects of dietary and supplemental g-tocopherol on health.

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Food High in Vitamin E and Who are likely to be Deficient

Food high in vitamin E include the following categories:
Almonds, Avocados, Brazil Nuts, Corn, Fortified Cereals, Hazelnuts, Safflower Nuts, Soybean Oil, Spinach, Sunflower Seeds and Walnuts.

Due to vitamin E is a fat-soluble vitamin, therefore, people who can not absorb dietary fat are always deficient in alpha tocopherol. Individuals who cannot absorb fat may require a vitamin E supplement because some dietary fat is needed for the absorption of vitamin E from the gastrointestinal tract. Anyone diagnosed with cystic fibrosis, individuals who have had part or all of their stomach removed, and individuals with malabsorptive problems such as Crohn’s disease may not absorb fat and should seriously consider to purchase some vitamin E supplements.

Besides people with low fat absorbtion ability, the following people should also consider getting some extra vitamin E to avoid deficiency and gain a better health:
- People more than 55 years of age
- Very low birth weight infants
- Those who have a chronic wasting illness
- Those who abuse alcohol or other drugs
- People with inadequate caloric or nutritional dietary intake or increased nutritional requirements
- Those with liver, gallbladder or pancreatic disease
- People with recent burns or injuries
- People under excess stress for long periods
- Anyone who has recently undergone surgery
- People with cystic fibrosis
- People with celiac disease
- People with hyperthyroidism
- Anyone at risk for myocardial infarction

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Vitamin E Deficiency Symptoms

Vitamin E deficiency has been observed in individuals with severe malnutrition, genetic defects affecting the a-tocopherol transfer protein, and fat malabsorption syndromes. For example, children with cystic fibrosis or cholestatic liver disease, who have an impaired capacity to absorb dietary fat and therefore fat-soluble vitamins, may develop symptomatic vitamin E deficiency. Severe vitamin E deficiency results mainly in neurological symptoms such as impaired balance and coordination, and muscle weakness. The developing nervous system appears to be especially vulnerable to vitamin E deficiency because children with severe vitamin E deficiency from birth, who are not treated with vitamin E, develop neurological symptoms rapidly. In contrast, individuals who develop malabsorption of vitamin E in adulthood may not develop neurological symptoms for 10-20 years. It should be noted that symptomatic vitamin E deficiency in healthy individuals who consume diets low in vitamin E has never been reported.

Although true vitamin E deficiency is rare, suboptimal intake of vitamin E is relatively common in the U.S. The National Health and Nutrition Examination Survey III (NHANES III) examined the dietary intake and blood levels of a-tocopherol in 16,295 multi-ethnic adults over the age of 18. Twenty seven % of white participants, 41 % of African Americans, 28% of Mexican Americans and 32% of the other participants were found to have blood levels of a-tocopherol less than 20 mmol/liter, a value chosen because the literature suggests an increased risk for cardiovascular disease below this level.

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Recent Studies on Vitamin E and Your Health

Vitamin E and Heart Disease and Stroke
Preliminary research has led to a widely held belief that vitamin E may help prevent or delay coronary heart disease. Researchers are fairly certain that oxidative modification of LDL-cholesterol (sometimes called "bad" cholesterol) promotes blockages in coronary arteries that may lead to atherosclerosis and heart attacks. Vitamin E may help prevent or delay coronary heart disease by limiting the oxidation of LDL-cholesterol. Vitamin E also may help prevent the formation of blood clots, which could lead to a heart attack. Observational studies have associated lower rates of heart disease with higher vitamin E intake. A study of approximately 90,000 nurses suggested that the incidence of heart disease was 30% to 40% lower among nurses with the highest intake of vitamin E from diet and supplements. The range of intakes from both diet and supplements in this group was 21.6 to 1,000 IU (32 to 1,500 mg), with the median intake being 208 IU (139 mg). A 1994 review of 5,133 Finnish men and women aged 30 - 69 years suggested that increased dietary intake of vitamin E was associated with decreased mortality (death) from heart disease. But even though these observations are promising, randomized clinical trials raise questions about the role of vitamin E supplements in heart disease. The Heart Outcomes Prevention Evaluation (HOPE) Study followed almost 10,000 patients for 4.5 years who were at high risk for heart attack or stroke. In this intervention study the subjects who received 265 mg (400) IU of vitamin E daily did not experience significantly fewer cardiovascular events or hospitalizations for heart failure or chest pain when compared to those who received a sugar pill. The researchers suggested that it is unlikely that the vitamin E supplement provided any protection against cardiovascular disease in the HOPE study. This study is continuing, to determine whether a longer duration of intervention with vitamin E supplements will provide any protection against cardiovascular disease.

Vitamin E and Cancer
Antioxidants such as vitamin E help protect against the damaging effects of free radicals, which may contribute to the development of chronic diseases such as cancer. Vitamin E also may block the formation of nitrosamines, which are carcinogens formed in the stomach from nitrites consumed in the diet. It also may protect against the development of cancers by enhancing immune function. Unfortunately, human trials and surveys that tried to associate vitamin E with incidence of cancer have been generally inconclusive.

Some evidence associates higher intake of vitamin E with a decreased incidence of prostate cancer and breast cancer. However, an examination of the effect of dietary factors, including vitamin E, on incidence of postmenopausal breast cancer in over 18,000 women from New York State did not associate a greater vitamin E intake with a reduced risk of developing breast cancer.

A study of women in Iowa provided evidence that an increased dietary intake of vitamin E may decrease the risk of colon cancer, especially in women under 65 years of age. On the other hand, vitamin E intake was not statistically associated with risk of colon cancer in almost 2,000 adults with cancer who were compared to controls without cancer. At this time there is limited evidence to recommend vitamin E supplements for the prevention of cancer.

Vitamin E and Cataracts
Cataracts are growths on the lens of the eye that cloud vision. They increase the risk of disability and blindness in aging adults. Antioxidants are being studied to determine whether they can help prevent or delay cataract growth. Observational studies have found that lens clarity, which is used to diagnose cataracts, was better in regular users of vitamin E supplements and in persons with higher blood levels of vitamin E. A study of middle aged male smokers, however, did not demonstrate any effect from vitamin E supplements on the incidence of cataract formation. The effects of smoking, a major risk factor for developing cataracts, may have overridden any potential benefit from the vitamin E, but the conflicting results also indicate a need for further studies before researchers can confidently recommend extra vitamin E for the prevention of cataracts.

Vitamin E and Immune Function
a-Tocopherol has been shown to enhance specific aspects of the immune response that appear to decline as people age. For example, 200 mg of synthetic a-tocopherol (equivalent to 100 mg of RRR-a-tocopherol) daily for several months increased the formation of antibodies in response to hepatitis B vaccine and tetanus vaccine in elderly adults. Whether a-tocopherol associated enhancements in the immune response actually translate to increased resistance to infections such as the flu (influenza virus) in older adults remains to be determined.

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Editors' summary on Vitamin E

Vitamin E is a fat-soluble vitamin. It is an essential vitamin that function as an antioxidant. Previous research has shown that vitamin E can help prevent cardiovascular disease and increase immune response as well as many other benefits.

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