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vitamin E

 
Dictionary: vitamin E
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n.
Any of several fat-soluble vitamins consisting of tocopherols, especially alpha-tocopherol, that are found chiefly in plant leaves, wheat germ oil, and milk and that act as antioxidants in the body.


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Sci-Tech Encyclopedia: Vitamin E
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A group of compounds, α, β, γ, and δ tocopherols, that have a chromanol ring and phytyl side chain and are widely distributed in nature, especially in edible vegetable oils (wheat germ, sunflower, cottonseed, safflower, canola, soybean, and corn oil). Unprocessed grains, nuts, and vegetables are other sources. When used as supplements, there are two vitamin E products available: natural source RRR α-tocopherol and synthetic all-rac-α-tocopherol. The latter is a mixture of eight different stereoisomers, of which only one is RRR α-tocopherol. See also Vitamin.

The terms “vitamin E” and “α-tocopherol” are frequently used interchangeably in human nutrition, but it is imperative to distinguish between supplements of RRR α-tocopherol and of synthetic α-tocopherol because their biological activity is different. Since the major function of vitamin E is to serve as a chain-breaking antioxidant, protecting cell membranes against free-radical damage, the most potent form of the vitamin should be used as a supplement. Although gastrointestinal absorption of all forms of vitamin E is equivalent, the subsequent physiological steps are sharply in favor of the RRR form. This action is mediated by a cellular liver transfer protein that is specific for the RRR form of α-tocopherol. It maintains the plasma level by selectively choosing the RRR form and recycling it into plasma lipoproteins for distribution of the vitamin to every tissue and organ in the body.

When deficiencies of the vitamin occur in humans as a consequence of acquired malabsorption or genetic abnormalities of lipoproteins or of the transfer protein, the major symptoms that develop are in the nervous system. Ataxia (lack of muscular coordination) and other neurologic symptoms result in severe incoordination and subsequent musculoskeletal changes.

The recommended daily allowance for vitamin E is 15 milligrams, which is present in the usual Western diet.

Food and Nutrition: vitamin E
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Generic descriptor for a group of fat-soluble compounds essential for reproduction in animals. Essential for human beings (not for reproduction, so far as is known) but rarely, if ever, deficient in the diet. Two main groups of compounds have vitamin E activity: the tocopherols and the tocotrienols; there are 4 isomers of each: α-, β-, γ, and δ-tocopherols and α-, β-, γ, and δ-tocotrienols, with differing vitamin potencies.

Vitamin E functions primarily as an antioxidant in cell membranes, protecting unsaturated fatty acids from oxidative damage.

The vitamin E content of foods is expressed as mg α-tocopherol equivalent (based on the different potency of the different vitamers). Vegetables, seeds, and most vegetable oils are good sources. In the UK and the EU an adequate intake is 0.4 mg/g dietary polyunsaturated fatty acid intake; the US/Canadian RDA is 15 mg/day. The obsolete international unit of vitamin E activity was equal to 1 mg of synthetic α-tocopherol; on this basis natural-source α-tocopherol is 1.49 iu/mg.

Food and Fitness: vitamin E
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anti-sterility factor; fertility vitamin

A group of related compounds called tocopherols which maintain the integrity of cell membranes. Vitamin E is an antioxidant and mutually protects vitamins A and C. Some coaches claim that it increases muscular development and function; this claim is hotly disputed, but there is considerable support for the suggestion that vitamin E reduces the oxygen requirements of muscles and so enhances performance. It has been suggested that physical endurance at high altitudes may be increased, and oxygen debt reduced, by taking 1200 IU of vitamin E per day. Such high doses can be toxic and should be taken only under medical supervision. Vitamin E is widely available in the diet. The richest sources include wheatgerm oil, sunflower oil, and roasted peanuts. Natural sources of Vitamin E are almost twice as potent as synthetic vitamin E. Natural and synthetic forms can be identified by subtle differences in the names of their main components: natural forms are known as ‘d-alpha tocopherol’ and the synthetic ones as ‘dl-alpha tocopherol’. Vitamin E deficiencies are rare, but when they do occur they may lead to destruction of red blood cells and anaemia. Deficiencies impair the reproductive ability of rats and causes muscle wasting in pigs, but vitamin E has no effect on human fertility or libido. There is a growing body of good evidence that vitamin E supplements may offer some protection against atherosclerosis and heart disease. It has also been suggested that supplements may reduce the risk of miscarriages, but this suggestion is disputed.

Dental Dictionary: vitamin E
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n

(tocopherol, tocotrienol antisterility factor), the tocopherol and tocotrienols have varying degrees of vitamin E activity but α-tocopherol is the most active. These fat-soluble compounds are found in eggs, muscle meats, liver, fish, chicken, oatmeal, and the oils of corn, soya, and cottonseed. In rats, the lack of vitamin E leads to fetus resorption in the female and atrophy of spermatogenic tissue with permanent sterility in the male. Vitamin E deficiency in humans is correlated with increased hemolysis of erythrocytes. The tocopherols prevent peroxidation of unsaturated fatty acids, and vitamin E requirements appear to be directly related to the dietary intake of unsaturated fatty acids. Although animals develop symptoms of muscular dystrophy on deficient diets, the vitamin has no effect on the human disease.

Drug Info: Vitamin E
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Brand names: Aquasol E®



Vitamin E tablets or capsules

What are vitamin E tablets or capsules?

ALPHA TOCOPHEROL (Vitamin E) helps protect the cells of your body from damaging chemical reactions, and it is important for the proper functioning of nerves and muscles. Vitamin E is a naturally occurring vitamin that is found in many foods such as cereal grains, fruits, green leafy vegetables, vegetable oils, and wheat germ oil. Vitamin E deficiency is rare because it is stored in body fat. Generic vitamin E tablets and capsules are available.

What should I tell my health care provider before I take this medicine?

They need to know if you have any of the following conditions:
• anemia
• blood clotting problems
• an unusual or allergic reaction to vitamin E, other medicines, foods, dyes, or preservatives

How should I take this medicine?

Take vitamin E tablets or capsules by mouth. Follow the directions on the prescription label. Swallow the tablets or capsules with a drink of water. Swallow capsules whole; do not crush or chew. Some tablets are chewable, read the directions carefully. Take exactly as directed. Do not take more than the recommended daily allowance.

Contact your pediatrician or health care professional regarding the use of this medicine in children. Special care may be needed.

What if I miss a dose?

If you miss a dose, forget it and take the next dose as usual. Do not take double or extra doses. There is no cause for concern if you miss a dose.

What drug(s) may interact with vitamin E?

• mineral oil
• orlistat
• porfimer PDT
• warfarin

Tell your prescriber or health care professional about all other medicines you are taking, including non-prescription medicines, nutritional supplements, or herbal products. Also tell your prescriber or health care professional if you are a frequent user of drinks with caffeine or alcohol, if you smoke, or if you use illegal drugs. These may affect the way your medicine works. Check with your health care professional before stopping or starting any of your medicines.

What should I watch for while taking vitamin E?

Visit your prescriber or health care professional for regular checks on your progress. Taking vitamin E supplements should not be a substitute for a balanced and varied diet. A good diet usually has enough vitamin E for your daily needs. Some foods that contain vitamin E include: cereal grains, fruits, green leafy vegetables, vegetable oils, and wheat germ oil.

What side effects may I notice from taking vitamin E?

The recommended daily allowance of vitamin E does not usually cause any side effects.
Side effects related to overdose include:
• blurred vision
• diarrhea
• dizziness
• headache
• nausea, vomiting
• stomach cramps
• unusual bleeding
• unusual tiredness or weakness

Where can I keep my medicine?

Keep out of the reach of children in a container that small children cannot open.

Store at room temperature between 15 and 30 degrees C (59 and 86 degrees F). Protect from light. Keep container tightly closed. Throw away any unused medicine after the expiration date.

Last updated: 7/1/2002

Important Disclaimer: The drug information provided here is for educational purposes only. It is intended to supplement, not substitute for, the diagnosis, treatment and advice of a medical professional. This drug information does not cover all possible uses, precautions, side effects and interactions. It should not be construed to indicate that this or any drug is safe for you. Consult your medical professional for guidance before using any prescription or over the counter drugs.

Alternative Medicine Encyclopedia: Vitamin E
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Description

Vitamin E is an antioxidant responsible for proper functioning of the immune system and for maintaining healthy eyes and skin. It is actually a group of fat soluble compounds known as tocopherols (i.e., alpha tocopherol and gamma tocopherol). Gamma tocopherol accounts for approximately 75% of dietary vitamin E. Vitamin E rich foods include nuts, cereals, beans, eggs, cold-pressed oils, and assorted fruits and vegetables. Because vitamin E is a fat soluble vitamin, it requires the presence of fat for proper absorption. Daily dietary intake of the recommended daily allowance (RDA) of vitamin E is recommended for optimum health.

Vitamin E is absorbed by the gastrointestinal system and stored in tissues and organs throughout the body. Certain health conditions may cause vitamin E depletion, including liver disease, celiac disease, and cystic fibrosis. Patients with end-stage renal disease (kidney failure) who are undergoing chronic dialysis treatment may be at risk for vitamin E deficiency. These patients frequently receive intravenous infusions of iron supplements, which can act against vitamin E.

Vitamin E deficiency can cause fatigue, concentration problems, weakened immune system, anemia, and low thyroid levels. It may also cause vision problems and irritability. Low serum (or blood) levels of vitamin E have also been linked to major depression.

General Use

Vitamin E is necessary for optimal immune system functioning, healthy eyes, and cell protection throughout the body. It has also been linked to the prevention of a number of diseases. The therapeutic benefits of vitamin E include:

  • Cancer prevention and treatment. Vitamin E is a known antioxidant, and has been associated with a reduced risk of gastrointestinal, cervical, prostate, lung, and possibly breast cancer. In addition to its role as a cancer preventive, vitamin E is being studied as a cancer treatment. It has been shown to inhibit the growth of prostate tumors and to induce apoptosis (cell self-destruction) in cancer cells. Vitamin E is also being investigated as an adjunctive treatment for cancer patients undergoing radiation therapy; it is thought that high doses of dietary antioxidants may increase the efficacy of the radiation treatment while protecting healthy cells against damage.
  • Immune system protection. Various studies have shown that vitamin E supplementation, particularly in elderly patients, boosts immune system function. Older patients have demonstrated improved immune response, increased resistance to infections, and higher antibody production. Vitamin E has also been used with some success to slow disease progression in HIV-positive patients.
  • Eye disease prevention. Clinical studies on vitamin E have shown that supplementation significantly reduces the risk for cataracts and for macular degeneration, particularly among women.
  • Memory loss prevention. Vitamin E deficiency has been linked to poor performance on memory tests in some elderly individuals.
  • Alzheimer's disease (AD) treatment. In a study performed at Columbia University, researchers found that Alzheimer's patients who took daily supplements of vitamin E maintained normal functioning longer than patients who took a placebo. In 2002, a group of Dutch epidemiologists reported on a much larger populationbased study conducted in the Netherlands between 1990 and 1993, with follow-up examinations in 1994 and 1999. The study confirmed the findings of the Columbia researchers, that high dietary intake of vitamin E lowers the risk of developing AD.
  • Liver disease treatment. Vitamin E may protect the liver against disease.
  • Diabetes treatment. Vitamin E may help diabetic patients process insulin more effectively. It has also been found to be effective in the treatment of diabetic neuropathy, a family of nerve disorders caused by diabetes. Vitamin E appears to reduce the symptoms of diabetic neuropathy and to improve the speed of transmission of nerve impulses.
  • Pain relief. Vitamin E acts as both an anti-inflammatory and analgesic (or pain reliever). Studies have indicated it may be useful for treatment of arthritis pain in some individuals.
  • Parkinson's disease prevention. High doses of vitamin E intake was associated with a lowered risk of developing Parkinson's disease in one 1997 Dutch study.
  • Tardive dyskinesia treatment. Individuals who take neuroleptic drugs for schizophrenia or other disorders may suffer from a side effect known as tardive dyskinesia, in which they experience involuntary muscle contractions or twitches. Vitamin E supplementation may lessen or eliminate this side effect in some individuals.
  • Porphyria treatment. Vitamin E has been found to be beneficial in treating patients with porphyria, a group of disorders characterized by abnormalities in the metabolism of blood pigments, by lowering the level of excretion of these blood pigments in the urine.

Other benefits of vitamin E are less clear cut, and have been called into question with conflicting study results or because of a lack of controlled studies to support them. These include:

  • Heart disease prevention. A number of epidemiological studies have indicated that vitamin E may prevent heart disease by lowering total blood cholesterol levels and preventing oxidation of LDL cholesterol. However, a large, controlled study known as the Heart Outcomes Prevention Evaluation (HOPE) published in early 2000 indicates that vitamin E does not have any preventative effects against heart disease. The study followed 9,500 individuals who were considered to be at a high risk for heart disease. Half the individuals were randomly chosen to receive vitamin E supplementation, and the other half of the study population received a placebo. After five years, there was no measurable difference in heart attacks and heart disease between the two patient populations. Still, vitamin E may still hold some hope for heart disease prevention. It is possible that a longer-term study beyond the five years of the HOPE study may demonstrate some heart protective benefits of vitamin E consumption. It is also possible that while the high-risk patient population that was used for the HOPE study did not benefit from vitamin E, an average-risk patient population might still benefit from supplementation. It is also possible that vitamin E needs the presence of another vitamin or nutrient substance to protect against heart disease. Further large, controlled, and long-term clinical studies are necessary to answer these questions.
  • Skin care. Vitamin E is thought to increase an individual's tolerance to UV rays when taken as a supplement in conjunction with vitamin C. Vitamin E has also been touted as a treatment to promote faster healing of flesh wounds. While its anti-inflammatory and analgesic properties may have some benefits in reducing swelling and relieving discomfort in a wound, some dermatologists dispute the claims of faster healing, and there are no large controlled studies to support this claim.
  • Hot flashes. In a small study conducted at the Mayo Clinic, researchers found that breast cancer survivors who suffered from hot flashes experienced a decrease in hot flashes after taking vitamin E supplementation.
  • Muscle maintenance and repair. Recent research has demonstrated that the antioxidative properties of vitamin E may prevent damage to tissues caused by heavy endurance exercises. In addition, vitamin E supplementation given prior to surgical procedures on muscle and joint tissues has been shown to limit reperfusion injury (muscle damage that occurs when blood flow is stopped, and then started again to tissues or organs).
  • Fertility. Vitamin E has been shown to improve sperm function in animal studies, and may have a similar effect in human males. Further studies are needed to establish the efficacy of vitamin E as a treatment for male infertility; as of 2002, its role in such treatment is still controversial.

Preparations

The U.S. recommended dietary allowance (RDA) of the alpha-tocopherol formulation of vitamin E is as follows:

  • men: 10 mg or 15 IU
  • women: 8 mg or 12 IU
  • pregnant women: 10 mg or 15 IU
  • lactating women: 12 mg or 18 IU

In April 2000, the National Academy of Sciences recommended changing the RDA for vitamin E to 22 international units (IUs), with an upper limit (UL), or maximum daily dose, of 1500 IUs. Daily values for the vitamin as recommended by the U.S. Food and Drug Administration, the values listed on food and beverage labeling, remain at 30 IUs for both men and women age four and older.

Many nuts, vegetable-based oils, fruits, and vegetables contain vitamin E. Foods rich in vitamin E include wheat germ oil (26.2 mg/tbsp), wheat germ cereal (19.5 mg/cup), peanuts (6.32 mg/half cup), soybeans (3.19 mg/cup), corn oil (2.87/tbsp), avocado (2.69 mg), and olive oil (1.68 mg/tbsp.). Grapes, peaches, broccoli, Brussels sprouts, eggs, tomatoes, and blackberries are also good sources of vitamin E. Fresh, raw foods contain the highest levels of the vitamin. Both heat and light can reduce vitamin and mineral potency in fresh foods, so overcooking and improper storage should be avoided. Sliced and chopped foods have more of their surface exposed to light, therefore keeping vegetables and fruits whole may also help to maintain full vitamin potency.

For individuals considered at risk for vitamin E deficiency, or those with an inadequate dietary intake, vitamin E supplements are available in a variety of different forms, including pills, capsules, powders, and liquids for oral ingestion. For topical use, vitamin E is available in ointments, creams, lotions, and oils. Vitamin E is also available commercially as one ingredient of a multivitamin formula.

The recommended daily dosage of vitamin E varies by individual need and by the amount of polyunsaturated fats an individual consumes. The more polyunsaturated fats in the diet, the higher the recommended dose of vitamin E, because vitamin E helps to prevent the oxidizing effects of these fats. Because vitamin E is fat soluble, supplements should always be taken with food.

Supplements are also available in either natural or synthetic formulations. Natural forms are extracted from wheat germ oil and other vitamin E food sources, and synthetic forms are extracted from petroleum oils. Natural formulas can be identified by a d prefix on the name of the vitamin (i.e., d-alpha-tocopherol).

Precautions

Overdoses of vitamin E (over 536 mg) can cause nausea, diarrhea, headache, abdominal pain, bleeding, high blood pressure, fatigue, and weakened immune system function.

Patients with rheumatic heart disease, iron deficiency anemia, hypertension, or thyroid dysfunction should consult their healthcare provider before starting vitamin E supplementation, as vitamin E may have a negative impact on these conditions.

Side Effects

Vitamin E is well-tolerated, and side effects are rare. However, in some individuals who are vitamin K deficient, vitamin E may increase the risk for hemorrhage or bleeding. In some cases, side effects may be decreased or eliminated by adjusting the dosage of vitamin E and vitamin K.

Although the reasons are not yet clear, high intake of vitamin E has been associated with a statistically significant increased risk of breast cancer in men.

Vitamin E ointments, oils, or creams may trigger an allergic reaction known as contact dermatitis. Individuals who are considering using topical vitamin E preparations for the first time, or who are switching the type of vitamin E product they use, should perform a skin patch test to check for skin sensitivity to the substance. A small, dime sized drop of the product should be applied to a small patch of skin inside the elbow or wrist. The skin patch should be monitored for 24 hours to ensure no excessive redness, irritation, or rash occurs. If a reaction does occur, it may be in response to other ingredients in the topical preparation, and the test can be repeated with a different vitamin E formulation. Individuals who experience a severe reaction to a skin patch test of vitamin E are advised not to use the product topically. A dermatologist or other healthcare professional may be able to recommend a suitable alternative.

Interactions

Individuals who take anticoagulant (blood thinning) or anticonvulsant medications should consult their healthcare provider before starting vitamin E supplementation. Vitamin E can alter the efficacy of these drugs.

It is important for persons taking supplemental vitamin E to tell their surgeon if they are scheduled for an operation. Vitamin E may interact with some of the medications given prior to or during surgery; it has also been shown to increase bleeding time if the patient is taking such other herbal preparations as feverfew or gingko biloba.

Non-heme, inorganic iron supplements destroy vitamin E, so individuals taking iron supplements should space out their doses (e.g., iron in the morning and vitamin E in the evening).

Large doses of vitamin A can decrease the absorption of vitamin E, so dosage adjustments may be necessary in individuals supplementing with both vitamins.

Alcohol and mineral oil can also reduce vitamin E absorption, and these substances should be avoided if possible in vitamin E deficient individuals.

Resources

Books

Reavley, Nocola. The New Encyclopedia of Vitamins, Minerals, Supplements, and Herbs. New York: M. Evans & Company, 1998.

Periodicals

Bolle, P., M. G. Evandri, and L. Saso. "The Controversial Efficacy of Vitamin E for Human Male Infertility." Contraception 65 (April 2002): 313-315.

Bonner, L. T., and E. R. Peskind. "Pharmacologic Treatments of Dementia." Medical Clinics of North America 86 (May 2002): 657-674.

Collins, S. C., and R. G. Dufresne Jr. "Dietary Supplements in the Setting of Mohs Surgery." Dermatologic Surgery 28 (June 2002): 447-452.

Engelhart, M. J., M. I. Geerlings, A. Ruitenberg, et al. "Dietary Intake of Antioxidants and Risk of Alzheimer's Disease." Journal of the American Medical Association 287 (June 26, 2002): 3261-3263.

Johnson, K. C., S. Pan, and Y. Mao. "Risk Factors for Male Breast Cancer in Canada, 1994-1998." European Journal of Cancer Prevention 11 (June 2002): 253-263.

Pinelli, A., S. Trivulzio, L. Tomasoni, et al. "High-Dose Vitamin E Lowers Urine Porphyrin Levels in Patients Affected by Porphyria Cutanea Tarda." Pharmacological Research 45 (April 2002): 355-359.

Prasad, K. N., W. C. Cole, B. Kumar, and K. Che Prasad. "Pros and Cons of Antioxidant Use During Radiation Therapy." Cancer Treatment Review 28 (April 2002): 79-91.

Sytze Van Dam, P. "Oxidative Stress and Diabetic Neuropathy: Pathophysiological Mechanisms and Treatment Perspectives." Diabetes/Metabolism Research and Reviews 18 (May-June 2002): 176-184.

"Vitamin E: E for Exaggerated?" Harvard Health Letter 25, no. 5 (March 2000):6(3p).

Yu, A., P. Somasundar, A. Balsubramaniam, et al. "Vitamin E and the Y4 Agonist BA-129 Decrease Prostate Cancer Growth and Production of Vascular Endothelial Growth Factor." Journal of Surgical Research 105 (June 1, 2002): 65-68.

Organizations

American Dietetic Association. 216 West Jackson Blvd., Chicago, IL 60606. (312) 899-0040. .

United States Department of Agriculture. Center for Nutrition Policy and Promotion. 1120 20th Street NW, Suite 200, North Lobby, Washington, D.C. 20036. (202) 418-2312. .

United States Food and Drug Administration (FDA). 5600 Fishers Lane, Rockville, MD 20857. (888) 463-6332. .

[Article by: Paula Ford-Martin; Rebecca J. Frey, PhD]

Britannica Concise Encyclopedia: vitamin E
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Fat-soluble organic compound found principally in certain plant oils and leaves of green vegetables. Vitamin E acts as an antioxidant in body tissues and may prolong life by slowing oxidative destruction of membranes. Certain rodents require it for normal reproduction. Besides uses in foods and in nutritional research and supplements, it is used to retard rancidity in fats, especially vegetable oils.

For more information on vitamin E, visit Britannica.com.

Sports Science and Medicine: vitamin E
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anti-sterility factor; fertility vitamin

A group of related compounds called tocopherols, believed to maintain the integrity of cell membranes. Vitamin E is an antioxidant and mutually protects vitamins A and C. It also acts as an anti-blood-clotting agent and has been used in the USA to treat some heart diseases. Some coaches claim that it increases muscular development and function; this claim is hotly disputed, but there is considerable support for the suggestion that vitamin E reduces the oxygen requirements of muscles and so enhances performance. Vitamin E is widely available in the diet. The richest sources include wheatgerm oil, sunflower oil, and roasted peanuts. Natural sources of vitamin E are almost twice as effective as synthetic vitamin F. Natural and synthetic forms can be identified by subtle differences in the names of their main components: natural forms are known as ‘d-alpha tocopherol’ and the synthetic ones as ‘dl-alpha tocopherol’. Deficiencies are rare, but when they do occur they may lead to destruction of red blood cells and anaemia. Deficiencies impair the reproductive ability of rats and cause muscle wasting in pigs. There is no strong evidence that vitamin E supplementation can help infertile human females, but large doses have been used to prevent miscarriages.

Veterinary Dictionary: vitamin E
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Α-tocopherol, one of the three tocopherols found in wheat germ. Acts as an antioxidant in the prevention of enzootic muscle dystrophy, mulberry heart disease, hepatosis dietetica and exudative diathesis and yellow fat disease, and deficiency of the vitamin is a major cause of these diseases.

  • v. E-responsive dermatosis — goats on selenium-deficient diets develop alopecia and seborrhea which responds to vitamin E supplementation; similar skin changes occurred in calves fed a milk substitute deficient in vitamin E.
Wikipedia: Tocopherol
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Tocopherols (or TCP) are a class of chemical compounds of which many have vitamin E activity. It is a series of organic compounds consisting of various methylated phenols. Because the vitamin activity was first identified in 1936 from a dietary fertility factor in rats, it was given the name "tocopherol" from the Greek words “τόκος” [birth], and “φέρειν”, [to bear or carry] meaning in sum "to carry a pregnancy," with the ending "-ol" signifying its status as a chemical alcohol.

Tocotrienols, which are related compounds, may also have vitamin E activity. All of these various derivatives with vitamin activity may correctly be referred to as "vitamin E." Tocopherols and tocotrienols are fat-soluble antioxidants but also seem to have many other functions in the body.

The compound α-tocopherol, a common form of tocopherol added to food products, is denoted by the E number E307.

Contents

Forms

Vitamin E exists in eight different forms, four tocopherols and four tocotrienols. All feature a chromanol 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. Both the tocopherols and tocotrienols occur in alpha, beta, gamma and delta forms, determined by the number of methyl groups on the chromanol ring. The tocotrienols differ from the analogous tocopherols by the presence of three double bonds in the hydrophobic side chain. Each form has slightly different biological activity.[1]

VitE.png

As a food additive, tocopherol is labeled with these E numbers: E307 (α-tocopherol), E308 (γ-tocopherol), and E309 (δ-tocopherol).

Alpha-tocopherol

Main article: alpha-Tocopherol

Alpha-tocopherol is the form of vitamin E that is preferentially absorbed and accumulated in humans.[2] The measurement of "vitamin E" activity in international units (IU) was based on fertility enhancement by the prevention of miscarriages in pregnant rats relative to alpha-tocopherol.

There are three stereocenters in alpha-tocopherol, so this is a chiral molecule.[3] The eight stereoisomers of alpha-tocopherol differ in the arrangement of groups around these stereocenters. In the image of RRR-alpha-tocopherol below, all three stereocenters are in the R form. However, if the middle of the three stereocenters were changed (so the hydrogen was now pointing down and the methyl group pointing up), this would become the structure of RSR-alpha-tocopherol. RSR-alpha-tocopherol and RRR-alpha-tocopherol are mirror-images of each other. These stereoisomers can also be named in an alternative older nomenclature, where the stereocenters are either in the d or l form.[4]

RRR stereoisomer of alpha-tocopherol, bonds around the stereocenters are shown as dashed lines (pointing down) or wedges (pointing up).

1 IU of tocopherol is defined as ⅔ milligrams of RRR-alpha-tocopherol (formerly named d-alpha-tocopherol or sometimes ddd-alpha-tocopherol). 1 IU is also defined as 1 milligram of an equal mix of the eight stereoisomers, which is a racemic mixture called all-rac-alpha-tocopheryl acetate. This mix of stereoisomers is often called dl-alpha-tocopheryl acetate, even though it is more precisely dl,dl,dl-alpha-tocopheryl acetate). However, 1 IU of this racemic mixture is not now considered equivalent to 1 IU of natural (RRR) α-tocopherol, and the Institute of Medicine and the USDA now convert IU's of the racemic mixture to milligrams of equivalent RRR using 1 IU racemic mixture = 0.45 "milligrams α-tocopherol".[5]

Tocotrienols

Tocotrienols, with four d- isomers, although less commonly known, also belong to the vitamin E family. The four tocotrienols have structures corresponding to the four tocopherols, except with an unsaturated bond in each of the three isoprene units that form the hydrocarbon tail, whereas Tocopherols have a saturated phytyl tail. Tocotrienol has been subject to fewer clinical studies and seen less research as compared to tocopherol. However, there is growing interest in the health effects of these compounds.[6]

History

During feeding experiments with rats Herbert McLean Evans concluded in 1922 that besides vitamins B and C, an unknown vitamin existed.[7] Although every other nutrition was present, the rats were not fertile. This condition could be changed by additional feeding with wheat germ. It took several years until 1936 when the substance was isolated from wheat germ and the formula C29H50O2 was determined. Evans also found that the compound reacted like an alcohol and concluded that one of the oxygen atoms was part of an OH (hydroxyl) group. As noted in the introduction, the vitamin was given its name by Evans from Greek words meaning "to bear young" with the addition of the -ol as an alcohol.[8] The structure was determined shortly thereafter in 1938.[9]

Recommended amounts

The U.S. Dietary Reference Intake (DRI) Recommended Daily Amount (RDA) for a 25-year old male for Vitamin E is 15 mg/day. The DRI for vitamin E is based on the alpha-tocopherol form because it is the most active form as originally tested. Results of two national surveys, the National Health and Nutrition Examination Survey (NHANES III 1988-91) and the Continuing Survey of Food Intakes of Individuals (1994 CSFII) indicated that the dietary intakes of most Americans do not provide the recommended amounts of vitamin E. However, a 2000 Institute of Medicine (IOM) report on vitamin E states that intake estimates of vitamin E may be low because energy and fat intake is often underreported in national surveys and because the kind and amount of fat added during cooking is often not known. The IOM states that most North American adults get enough vitamin E from their normal diets to meet current recommendations. However, they do caution individuals who consume low fat diets because vegetable oils are such a good dietary source of vitamin E. "Low-fat diets can substantially decrease vitamin E intakes if food choices are not carefully made to enhance alpha-tocopherol intakes". Vitamin E supplements are absorbed best when taken with meals.[10]

Because vitamin E can act as an anticoagulant and may increase the risk of bleeding problems, many agencies have set an upper tolerable intake level (UL) for vitamin E at 1,000 mg (1,500 IU) per day.[11]

Sources

In foods, the most abundant sources of vitamin E are vegetable oils such as palm oil, sunflower, corn, soybean, and olive oil. Nuts, sunflower seeds, seabuckthorn berries, kiwifruit, and wheat germ are also good sources. Other sources of vitamin E are whole grains, fish, peanut butter, goats milk, and green leafy vegetables. Fortified breakfast cereals are also an important source of vitamin E in the United States. Although originally extracted from wheat germ oil, most natural vitamin E supplements are now derived from vegetable oils, usually soybean oil.

The content of Vitamin E for rich sources follows:[12]

Deficiency

Main article: Vitamin E deficiency

Vitamin E deficiency causes neurological problems due to poor nerve conduction. These include neuromuscular problems such as spinocerebellar ataxia and myopathies.[4] Deficiency can also cause anemia, due to oxidative damage to red blood cells.

Supplements

Commercial vitamin E supplements can be classified into several distinct categories:

  • Fully synthetic vitamin E, "dl-alpha-tocopherol", the most inexpensive, most commonly sold supplement form usually as the acetate ester;
  • Semi-synthetic "natural source" vitamin E esters, the "natural source" forms used in tablets and multiple vitamins. These are highly fractionated d-alpha tocopherol or its esters, often made by synthetic methylation of gamma and beta d,d,d tocopherol vitamers extracted from plant oils.
  • Less fractionated "natural mixed tocopherols" and high d-gamma-tocopherol fraction supplements

Synthetic all-racemic

Synthetic vitamin E derived from petroleum products is manufactured as all-racemic alpha tocopheryl acetate with a mixture of eight stereoisomers. In this mixture, one alpha-tocopherol molecule in eight molecules are in the form of RRR-alpha-tocopherol (12.5% of the total).[13]

The 8-isomer all-rac vitamin E is always marked on labels simply as dl-tocopherol or dl-tocopheryl acetate, even though it is (if fully written out) actually dl,dl,dl-tocopherol. The present largest manufacturers of this type are DSM and BASF.

(An earlier semisynthetic vitamin E actually contained 50% d,d,d-alpha tocopherol moiety and 50% l,d,d-alpha-tocopherol moiety, as synthesized by an earlier process which started with a plant sterol intermediate with the correct chirality in the tail, and thus resulted in a racemic mixture at only one chiral center. This form, known as 2-ambo tocopherol, is no longer made.)

Natural alpha-tocopherol is the RRR-alpha (or ddd-alpha) form. The synthetic dl,dl,dl-alpha ("dl-alpha") form is not as active as the natural ddd-alpha ("d-alpha") tocopherol form. This is mainly due to reduced vitamin activity of the 4 possible stereoisomers which are represented by the l or S enantiomer at the first stereocenter (an S or l configuration between the chromanol ring and the tail, i.e., the SRR, SRS, SSR, and SSS stereoisomers).[3] Unnatural 2R stereoisomers with natural R configuration at this stereocenter, but S at the other centers in the tail (RSR, RRS), appear to retain substantial RRR vitamin activity because they are recognized by the alpha-tocopherol transport protein, and thus maintained in the plasma, where the other four stereoisomers are not. Thus, the synthetic all-rac-α-tocopherol probably has only about half the vitamin activity of RRR-alpha-tocopherol in humans, even though the ratio of activities of the 8 stereoisomer racemic mixture to the natural vitamin is 1 to 1.36 in the rat pregnancy model.[14]

Although it is clear that mixtures of stereoisomers are not as active as the natural RRR-alpha-tocopherol form, in the ratios discussed above, specific information on any side effects of the seven synthetic vitamin E stereoisomers is not readily available.

Esters

Manufacturers also commonly convert the phenol form of the vitamins (with a free hydroxyl group) to esters, using acetic or succinic acid. These tocopheryl esters are more stable and are easy to use in vitamin supplements. Alpha tocopheryl esters are de-esterified in the gut and then absorbed as the free tocopherol.[15][16] Tocopheryl nicotinate and tocopheryl linolate esters are also used in cosmetics and some pharmaceuticals.

Alpha tocopheryl acetate, an acetate ester of alpha-tocopherol.

An initial study in humans saw large variability between different people's absorption of all these forms of vitamin E, with no statistically-significant differences seen between tocopheryl esters and the free tocopherol.[17] Later studies saw no difference between the rate of absorption of these forms of vitamin E and found that tocopheryl esters and free tocopherol had the same bioavailability.[18][19] The esterase activity responsible for releasing the free tocopherol may be reduced in children with cystic fibrosis.[20]

Mixed tocopherols

"Mixed tocopherols" in the US contain at least 20% w/w other natural R, R,R- tocopherols, i.e. R, R,R-alpha-tocopherol content plus at least 25% R, R,R-beta-, R, R,R-gamma-, R, R,R-delta-tocopherols.

Some brands may contain 200% w/w or more of the other tocopherols and measurable tocotrienols. Some mixed tocopherols with higher gamma-tocopherol content are marketed as "High Gamma-Tocopherol." The label should report each component in milligrams, except R, R,R-alpha-tocopherol may still be reported in IU. Mixed tocopherols can also be found in other nutritional supplements.

Other uses

Age-related macular degeneration (AMD)

Age-related macular degeneration (AMD) is the leading cause of visual impairment and blindness in the United States and the developed world among people 65 years and older. It has been shown that vitamin E alone does not attenuate the development or progression of AMD.[21]

However, studies focusing on efficacy of Vitamin E combined with other antioxidants, like zinc and vitamin C, indicate a protective effect against the onset and progression of AMD.[22][23][24]

Alternative medicine

A variety of schools of alternative medicine advocate high intake of dietary or supplementary vitamin E. A review of a number of randomized controlled trials in the scientific literature by the Cochrane Collaboration published in JAMA in 2007 also found an increase in mortality, of 4% (Relative Risk 1.04, 95% confidence interval 1.01-1.07).[25] Excessive intake of vitamin E may increase risk of bleeding. A 2005 meta-analysis found that high-dosage vitamin E supplements may increase all-cause mortality.[26] "High dose" vitamin E esters (>400 units/day) were also associated with an increased risk in all-cause mortality of 39 per 10,000 persons, and a statistically significant relation existed between dose and mortality, with increased risk at doses exceeding 150 units per day. The Miller study was criticised in the Journal of the American Nutraceutical Association.[27]

Proponents of megavitamin, orthomolecular, and naturally based therapies have for the last two thirds of a century advocated and used the natural tocopherols, often mixed tocopherols with an additional 25% - 200% w/w d-beta-, d-gamma-, and d-delta-tocopherol.[28][29] Studies on vitamin E have largely concentrated on use of either a synthetic all-racemic ("d, l-") alpha tocopheryl ester (acetate or succinate) or a semi-synthetic d-alpha tocopheryl ester (acetate or succinate).

Alzheimer's disease

Alzheimer's disease is a wasting disease of the brain. As oxidative stress may be involved in the pathogenesis of Alzheimer's, tocopherols have been tested as both a means of prevention and treatment. The results of these studies have been mixed, with some research suggesting that high levels of vitamin E in the diet may reduce the risk of Alzheimer's, while other studies found no such link.[30] Studies on progression have also been contradictory, with the Alzheimer’s Disease Cooperative Study suggesting that vitamin E supplementation might be beneficial, but a later trial finding no clinical benefit.[31] Due to this contradictory and confusing evidence, vitamin E or tocopherol supplements are not currently recommended for treating or preventing Alzheimer's disease.[32]

Cancer

As of 2009, human trials and surveys that have investigated potential association of vitamin E intake with incidence of cancer remain generally inconclusive. 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.

Some evidence associates higher intake of vitamin E with a decreased incidence of prostate cancer (see ATBC study) and breast cancer. Some studies correlate additional cofactors, such as specific vitamin E isomers, e.g. gamma-tocopherol, and other nutrients, e.g. selenium, with dramatic risk reductions in prostate cancer.[33] 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 the effect on lung cancer in smokers also showed no benefit.[34]

Recent studies have found that increased intake of vitamin E, especially among smokers may be responsible for an increase in the incidence of lung cancer, with one study finding an increase in the incidence of lung cancer by 7% for each 100 IU of vitamin E taken daily.[35][36][37][38]

Cataracts

Antioxidants are being studied to determine whether they can help prevent or delay age-related growth of cataracts, a clouding of the tissue of the lens of the eye. 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 controlled trial of high doses of vitamins C and E and beta carotene found no effect on the risk of developing cataracts.[39] Similarly, a trial using vitamin E alone found that vitamin E supplementation produced no change in the risk of developing cataracts or the rate of progression of existing cataracts.[40]

Glaucoma

A 2007 study published in the European Journal of Ophthalmology found that, along with other treatments for glaucoma, adding alpha-tocopherol appeared to help protect the retina from glaucomatous damage. Groups receiving 300 mg and 600 mg per day of alpha-tocopherol, delivered orally, showed statistically significant decreases in the resistivity index in the posterior ciliary arteries and in the pulsatility index in the ophthalmic arteries, after six and twelve months of therapy. Alpha-tocopherol-treated patients also had significantly lower differences in mean visual field deviations."[41]

Heart disease

Preliminary research has led to a widely held belief that vitamin E may help prevent or delay coronary heart disease, but larger controlled studies have not shown any benefit.[42] Many researchers advance the belief that oxidative modification of LDL-cholesterol (sometimes called "bad" cholesterol) promotes blockages in coronary arteries that may lead to atherosclerosis and heart attacks.[citation needed] 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.

Despite these promising observations, randomized clinical trials have consistently shown lack of benefit to 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.

Furthermore, meta analysis of several trials of antioxidants, including vitamin E, have not shown any benefit to vitamin E supplementation for preventing coronary heart disease.[43] One study suggested that Vitamin E (as alpha-tocopherol only) supplementation may increase the risk for heart failure.[44] Supplementing alpha-tocopherol without gamma-tocopherol is known to lead to reduced serum gamma- and delta-tocopherol concentrations.[45]

On September 10, 2007, the American Heart Association (in its journal Circulation) stated that women taking regular doses of vitamin E or Tocopherol were 21% less likely to suffer a blood clot. Dr. Robert Glynn of Harvard Medical School said (it was an interesting finding but not yet proven and) further research must confirm the link in the prevention of venous thromboembolism, and patients must not stop taking prescribed blood thinners.[46]

Parkinson's disease

In May 2005, The Lancet Neurology published a study suggesting that vitamin E may help protect against Parkinson's disease.[47] Individuals with moderate to high intakes of dietary vitamin E were found to have a lower risk of Parkinson's. No conclusion could be made whether supplemental vitamin E has the same effect.[48] Other trials have tested whether giving vitamin E supplements reduces the risk of Parkinson's disease, or if they can slow the progression of the disease. In a 1998 study, vitamin E supplements had no effect on the rate of progression.[49]

Pregnancy

Recent studies into the use of both vitamin C and the single isomer vitamin E esters as possible aids in preventing oxidative stress leading to pre-eclampsia has failed to show significant benefits,[50] but did increase the rate of babies born with a low birthweight in one study.[51]

Preservative

Tocopherols are sometimes used as a food preservative to prevent oils from going rancid.[citation needed]

Topical use

Vitamin E is widely used as an inexpensive antioxidant in cosmetics and foods. Vitamin E containing products are commonly used in the belief that vitamin E is good for the skin; many cosmetics include it, often labeled as tocopherol acetate, tocopheryl linoleate or tocopheryl nicotinate. Some individuals experience allergic reactions to some tocopheryl esters or develop a rash and hives that may spread over the entire body from the use of topical products with alpha tocopheryl esters.[52]

Vitamin E is often claimed by manufacturers of skin creams and lotions to play a role in encouraging skin healing and reducing scarring after injuries such as burns on the basis of limited research,[53] but the weak evidence of a benefit of silicon gel sheeting with or without added Vitamin E is limited by the poor quality of the research.[54] One study found that it did not improve or worsen the cosmetic appearance in 90% of patients, with a third developing contact dermatitis.[55]

See also

References

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External links

v • d • e
Vitamins (A11)
Fat soluble
Tocopherol (Alpha, Beta, Gamma, Delta) · Tocotrienol · Tocofersolan
Water soluble

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