Tocopherol

From Wikipedia, the free encyclopedia

For the use of the slang term Vitamin E to refer to recreational drugs, see Methylenedioxymethamphetamine (MDMA)
α-Tocopherol [1]
α-Tocopherol
Chemical name (2R)-2,5,7,8-Tetramethyl-2-[(4R,8R)-4,8,12
-trimethyltridecyl]-3,4-dihydro-2H-chromen-6-ol
Chemical formula C29H50O2
Molecular mass 430.69 g/mol
CAS number [59-02-9]
Density 0.950 g/cm3
Melting point 2.5-3.5 °C
Boiling point 200-220 °C at 0.1 mmHg
SMILES CC(C)CCC[C@@H](C)CCC[C@@H](C)CCC
[C@]1(C)CCc2c(C)c(O)c(C)c(C)c2O1
Disclaimer and references

Tocopherol, or vitamin E, is a fat-soluble vitamin in eight forms that is an important antioxidant. Vitamin E is often used in skin creams and lotions because it is claimed by the manufacturers to play a role in encouraging skin healing and reducing scarring after injuries such as burns.

Natural vitamin E exists in eight different forms or isomers, four tocopherols and four tocotrienols. All isomers have a chromanol ring, with a hydroxyl group which can donate a hydrogen atom to reduce free radicals and a hydrophobic side chain which allows for penetration into biological membranes. There is an alpha, beta, gamma and delta form of both the tocopherols and tocotrienols, determined by the number of methyl groups on the chromanol ring. Each form has its own biological activity, the measure of potency or functional use in the body.

Contents

[edit] Sources of vitamin E

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, and wheat germ are also good sources. Other sources of vitamin E are whole grains, fish, peanut butter, 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 actual content of Vitamin E for rich sources is stated in the following list:[2]

[edit] Forms of vitamin E

Alpha-tocopherol is traditionally recognized as the most active form of vitamin E in humans, and is a powerful biological antioxidant. The measurement of "vitamin E" activity in international units (IU) was based on fertility enhancement by the prevention of spontaneous abortions in pregnant rats relative to alpha tocopherol. It increases naturally to about 150% of normal in the maternal circulation during human pregnancies. 1 IU of vitamin E is defined as the biological equivalent of 0.667 milligrams of RRR-alpha-tocopherol (formerly named d-alpha-tocopherol, or of 1 milligram of all-rac-alpha-tocopheryl acetate (commercially called dl-alpha-tocopheryl acetate, the original d,l- synthetic molecular mix, properly named 2-ambo-alpha-tocopherol, is no longer manufactured). The other R,R,R tocopherol vitamers are slowly being recognized as research begins to elucidate their additional roles in the human body. Many naturopathic and orthomolecular medicine advocates suggest that vitamin E supplements contain at least 20% by weight of the other natural vitamin E isomers. Commercially available blends of natural vitamin E include "mixed tocopherols" and "high gamma tocopherol" formulas. Also selenium, Coenzyme Q10, and ample vitamin C have been shown to be needed for effective antioxidant recycling of tocopherols.

Tocotrienols, with four d- isomers, 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. Tocopherols have a saturated phytyl tail.

Antioxidants such as vitamin E act to protect 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. Vitamin C and other anti-oxidants recycle vitamin E end-products back into effective suppressors of free radicals. Studies are underway to determine whether vitamin E might help prevent or delay the development of those chronic diseases.

Commercial vitamin E supplements can be classified into several distinct categories: fully synthetic vitamin E, "d,l-alpha-tocopherol", the most inexpensive, most commonly sold supplement form usually as the acetate ester; semisynthetic "natural source" vitamin E esters, the "natural source" forms used in tablets and multiple vitamins; highly fractionated natural d-alpha tocopherol; less fractionated "natural mixed tocopherols"; high gamma-tocopherol fraction supplements; and tocotrienol supplements.

Synthetic vitamin E is now manufactured as all-racemic alpha tocopheryl acetate with three chiral centers, with only one alpha tocopherol molecule (moiety) in 8 molecules as actual R,R,R-alpha tocopherol. Synthetic all-rac vitamin E is usually marked as d,l-tocopherol or d,l-tocopheryl acetate, with 50% d-alpha tocopherol moiety and 50% l-alpha-tocopherol moiety, as synthesized by an earlier process with only one chiral center. The synthetic form is not as active as the natural alpha tocopherol form. The 1950's thalidomide disaster with numerous severe birth defects is a common example of d- vs l- epimer forms type problem with synthesized racemic mixtures. Information on any side effects of the synthetic vitamin E epimers is not readily available. Naturopathic and orthomolecular medicine advocates have long considered the synthetic vitamin E forms to be with little or no merit for cancer, circulatory and heart diseases.

Semisynthetic "natural source" vitamin E, manufacturers convert the common natural beta, gamma and delta tocopherol isomers into esters using acetic or succinic acid and add methyl groups to yield d-alpha tocopheryl esters such as d-alpha tocopheryl acetate or d-alpha tocopheryl succinate. These tocopheryl esters are more stable and are easy to use in tablets and multiple vitamin pills. Because only alpha tocopherols were officially counted as "vitamin E" in supplements, refiners and manufacturers faced enormous economic pressure to esterify and methylate the other natural tocopherol isomers, d-beta-, d-gamma- and d-delta-tocopherol into d-alpha tocopheryl acetate or succinate. However these alpha tocopheryl esters have been shown to be variably and less efficiently absorbed in humans than in the original normative tests using rats.[3] Tocopheryl nicotinate and tocopheryl linolate esters are used in cosmetics and some pharmaceuticals. In the healthy human body, the semisynthetic forms are easily de-esterified over several days, primarily in the liver, but not for common problems in premature babies, aged or ill patients.

"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 premium 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.

[edit] 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. This is approximately 15 IU/day. Specifically, The natural form of alpha-tocopherol: RRR-alpha-tocopherol maintain 1.5 IU/mg.

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. (Iuliano 2001) 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.[4]

[edit] Factors in vitamin E deficiency

There are three specific situations when a vitamin E deficiency is likely to occur. It is seen in persons who cannot absorb dietary fat, has been found in premature, very low birth weight infants (birth weights less than 1500 grams, or 3.5 pounds), and is seen in individuals with rare disorders of fat metabolism. A vitamin E deficiency is usually characterized by neurological problems due to poor nerve conduction.

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, liver disease or pancreatic insufficiency may not absorb fat and should discuss the need for supplemental vitamin E with their physician (3). People who cannot absorb fat often pass greasy stools or have chronic diarrhea.

Very low birth weight infants may be deficient in vitamin E. These infants are usually under the care of a neonatologist, a pediatrician specializing in the care of newborns, who evaluates and treats the exact nutritional needs of premature infants.

Abetalipoproteinemia is a rare inherited disorder of fat metabolism that results in poor absorption of dietary fat and vitamin E. The vitamin E deficiency associated with this disease causes problems such as poor transmission of nerve impulses, muscle weakness, and degeneration of the retina that can cause blindness. Individuals with abetalipoproteinemia may be prescribed special vitamin E supplements by a physician to treat this disorder.

Also, in adults, erythrocyte membrane fragility results as the erythrocytes are oxidized.

[edit] Current issues and controversies about vitamin E

Conventional medical studies on "vitamin E", as of 2006 and as below, use either a synthetic all-racemic ("d,l-") alpha tocopheryl ester (acetate or succinate) or a semi-synthetic d-alpha tocopheryl ester (acetate or succinate). Proponents of megavitamin, orthomolecular and naturally based therapies have advocated, for the last two thirds of a century, and have used the natural tocopherols, often mixed tocopherols with an additional 25% - 200% w/w d-beta-, d-gamma-,[5][6] and d-delta-tocopherol. Based on various clinical, experimental, patent, and individual data, natural health proponents have long held[7][8] that the other poorly studied tocopherols, especially the abundant d-gamma-tocopherol,[9] in combination with other antioxidants such as selenium, coQ10, vitamin C, vitamin K2, mixed carotenoids, and lipoic acid, provide unique biochemical benefits.[10] The methodology, interpretation and reporting of conventional vitamin E studies have even become contentious within conventional medicine circles.[11]

[edit] Vitamin E and heart disease

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 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.[12] Indeed, vitamin E supplementation may increase the risk for heart failure.[13]

Orthomolecular and naturopathetic medicine use much different types of vitamin E, the natural mixed tocopherols, and other supportive cofactors such as, selenium, vitamin C, carnitine, lysine, and co-Q10 for various cardiovascular diseases.[14][15] See also Orthomolecular_medicine:Vitamin E controversy.

[edit] 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. To date, human trials and surveys that have tried to associate vitamin E with incidence of cancer remain generally inconclusive.

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.[16] 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.

Recent studies also show that vitamin E acts as an effective free radical scavenger and can lower the incidence of lung cancer in smokers. The effects are opposite to that of the clinical trials based on administering carotenoid to male smokers, that resulted in increased risk of lung cancer. Hence vitamin E is an effective antagonist to the oxidative stress that is imposed by high carotenoids in certain patients.

[edit] Vitamin E and cataracts

A cataract is a condition of clouding of the tissue of the lens of the eye. 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. It is important to note that the term "cataract" may be used in common parlance for an opacity involving any tissue of the eye, for example a corneal scar. Thus a character in theater or on television who is blind from cataracts might have white instead of clear corneas, covering over the iris and pupil. Since the lens is behind the pupil, real cataracts are difficult to see without special instrumentation, so people with cataracts have rather normally appearing eyes.

[edit] Vitamin E and Age Related Macular Degeneration (AMD)

AMD is the leading cause of visual impairment and blindness in the United States and the developed world among people 65 years and older. Roughly 30% of the human population 75 years or older has some degree of AMD. As the average life span of humans continues to increase, particularly in the developed countries, the incidence of AMD is expected to nearly double within the next 25 years. What is particularly devastating about advanced forms of this condition is that it involves loss of central vision - affecting abilities to read and see faces. A randomized, placebo-controlled Age-Related Eye Disease Study (AREDS) trial sponsored by the National Eye Institutes showed that people at high risk of developing advanced stages of AMD lowered their risk by about 25 percent when treated for 5 years with a high-dose combination of vitamin C, vitamin E, beta-carotene, and zinc. Studies on vitamin E alone have been contradictory at best, with some showing no association between levels of vitamin E intake and progression of AMD.

[edit] Vitamin E and Alzheimer's disease

Alzheimer's disease is a wasting disease of the brain. An observational trial conducted by The Johns Hopkins University Bloomberg School of Public Health found that when vitamin E is taken daily in large doses (400-1000IU) in combination with vitamin C (500-1000mg) the onset of Alzheimer's was reduced between 64 and 78%.[17]

[edit] Vitamin E and Parkinson's disease

In May 2005, The Lancet Neurology published a study suggesting that vitamin E may help protect against Parkinson's disease. Individuals with moderate to high intakes of dietary vitamin E were found to have a lower risk of Parkinson's. No conclusion was drawn about whether supplemental vitamin E has the same effect, however.[18]

[edit] Health issues of vitamin E supplementation

The overall wisdom of synthetic and semisynthetic vitamin E supplementation has been increasingly questioned in recent years. A controversial[10] 2005 meta analysis of vitamin E esters supplementation questioned the benefit of high dosage alpha tocopheryl esters.[19] This meta analysis found that "high dose" vitamin E esters(>400 units/day) were associated with an all cause mortality risk difference of 39 per 10,000 persons, including some trials using synthetic beta-carotene and other cofounders to supply the mortality. Further, the Miller group claimed a significant relationship between dose and all-cause mortality, with increased risk with doses exceed 150 units per day.

However, "toxicity symptoms have not been reported even at intakes of 800 IU per kilogram of body weight daily for 5 months" according to the Food and Nutrition Board (Rosenberg, et al), an amount that corresponds to 60,000 IU per day for a 75 kg adult.

[edit] Use during pregnancy

Recent studies into the use of both Vitamin C and the single isomer vitamin E esters as possible help in preventing oxidative stress leading to pre-eclampsia has failed to show significant benefits,[20] but did increase the rate of babies born with a low birthweight in one study.[21] However, earlier work that suggested vitamin K (similar structures to natural E isomers) and C together have 91% benefit in nausea and vomiting remains unaddressed.[22]

[edit] See Also

[edit] Notes

  1. ^ Merck Index, 11th Edition, 9931.
  2. ^ J. Bauernfeind in: L. J. Machlin (ed.): Vitamin E – A Comprehensive Treatise, Marcel Dekker, New York 1980, p. 99
  3. ^ Horwitt MK, et al, Serum concentrations of a-tocopherol after ingestion of various vitamin E preparations, Am J Clin Nutr 1984;40: 240-245. The rat-fetal-resorption test currently is used to assess the biological activity of vitamin E compounds. Previous studies in humans, however, suggest that rat assays underestimate the potency of free tocopherol relative to the acetate ester form and of RRR-a-tocopheryl acetate relative to all-rac-a-tocopheryl acetate. Therefore, we studied...20 adult human subjects. Measurements...of 800 IU of the various preparations...at 24 h...mean increase in concentration of a-tocopherols (mg/g lipid) in 24 h was 71.2% after RRR-a-tocopherol, 63.3% after RRR-a-tocopher[yl] acetate plus apple pectin, 60.9% after RRR-a-tocopher[yl] acetate, 31.6% after all-rac-a-tocopher[yl] acetate, and 41.2% after RRR-a-tocopher[yl] succinate. Animal assay data do not correlate with data from studies of absorption and retention in serum of a-tocopherols ingested by humans.
  4. ^ Vitamin E Fact sheet
  5. ^ Jiang Q et al.Gamma tocopherol, the major form of vitamin E in the US diet, deserves more attention. Am J Clin Nutr 2001; 74: 714-22.
  6. ^ JM Gaziano, Vitamin E and Cardiovascular Disease: Observational Studies, Ann. N.Y. Acad. Sci. 1031: 280–291 (2004) "
  7. ^ Bailey H (1964) Vitamin E: Your Key to a Healthy Heart, Chilton Books, ASIN B000GS9VPQ Bailey describes mixed tocopherols use for CVD back to the 1940s
  8. ^ Walker M, New/Old Findings on Unique Vitamin E, Townsend Letter for Doctors and Patients, No. 111, 1992, p. 826
  9. ^ MacWilliam L,What Makes Gamma Tocopherol Superior to Alpha Tocopherol, LE Magazine, Report, April 2006
  10. ^ a b M. Houston, “Meta-Analysis, Metaphysics and Mythology” JANA Vol. 8 No. 1, 2005 original
  11. ^ Carter, T. Responses and Comments: High-Dosage Vitamin E Supplementation and All-Cause Mortality, Ann Intern Med. 2005 Jul 19;143(2):155; responses 150-160
  12. ^ Vivekananthan D, Penn M, Sapp S, Hsu A, Topol E (2003). "Use of antioxidant vitamins for the prevention of cardiovascular disease: meta-analysis of randomised trials.". Lancet 361 (9374): 2017-23. PMID 12814711.
  13. ^ Lonn E, Bosch J, Yusuf S, Sheridan P, Pogue J, Arnold J, Ross C, Arnold A, Sleight P, Probstfield J, Dagenais G (2005). "Effects of long-term vitamin E supplementation on cardiovascular events and cancer: a randomized controlled trial.". JAMA 293 (11): 1338-47. PMID 15769967.
  14. ^ Saul A. Shute Vitamin E Treatment Protocol. DoctorYourSelf.com
  15. ^ Saul A. Congestive Heart Failure. DoctorYourSelf.com, 2003.
  16. ^ [1]
  17. ^ Johns Hopkins press release
  18. ^ BBC News
  19. ^ Miller E, Pastor-Barriuso R, Dalal D, Riemersma R, Appel L, Guallar E (2005). "Meta-analysis: high-dosage vitamin E supplementation may increase all-cause mortality.". Ann Intern Med 142 (1): 37-46. PMID 15537682.
  20. ^ Rumbold A, Crowther C, Haslam R, Dekker G, Robinson J (2006). "Vitamins C and E and the risks of preeclampsia and perinatal complications.". N Engl J Med 354 (17): 1796-806. PMID 16641396.
  21. ^ Poston L, Briley A, Seed P, Kelly F, Shennan A (2006). "Vitamin C and vitamin E in pregnant women at risk for pre-eclampsia (VIP trial): randomised placebo-controlled trial.". Lancet 367 (9517): 1145-54. PMID 16616557.
  22. ^ Pizzorno JE, Murray MT (November 2005) Textbook of Natural Medicine, 3rd edition, Churchill Livingstone, ISBN 0-443-07300-7, pg 1942 Vitamin K and C, when used together, have shown considerable clinical efficacy, with 91% of patients in one study showing complete remission of nausea and vomiting within 72 hours. Both vitamins alone show little effect.

[edit] References

  • Institute of Medicine, Food and Nutrition board. Dietary Reference Intakes: Vitamin C, Vitamin E, Selenium, and Carotenoids. National Academy Press, Washington, DC, 2000.
  • U.S. Department of Agriculture, Agricultural Research Service, 1999. USDA Nutrient Database for Standard Reference, Release 13. Nutrient Data Laboratory Home Page, http://www.nal.usda.gov/fnic/foodcomp
  • Dietary Guidelines Advisory Committee, Agricultural Research Service, www.softecare.com United States Department of Agriculture (USDA). Report of the Dietary Guidelines Advisory Committee on the Dietary Guidelines for Americans, 2000. http://www.ars.usda.gov/dgac
  • Rosenberg H and Feldzamen AN. The book of vitamin therapy. New York: Berkley Publishing Corp, 1974.
  • L. Iuliano; F. Micheletta; M. Maranghi; G. Frati; U. Diczfalusy; F. Violi (2001). "Bioavailability of Vitamin E as Function of Food Intake in Healthy Subjects". Arteriosclerosis, Thrombosis, and Vascular Biology 21: e34–e37. PMID 11597949.
  • The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. The Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group, N Engl J Med, 330 (15): 1029-35

[edit] External links


Vitamins
Retinol (A) | B vitamins (Thiamine (B1), Riboflavin (B2), Niacin (B3), Pantothenic acid (B5), Pyridoxine (B6), Biotin (B7), Folic acid (B9), Cyanocobalamin (B12)) | Choline | Ascorbic acid (C) | Ergocalciferol and Cholecalciferol (D) | Tocopherol (E) | Naphthoquinone (K)
Retrieved from "http://en.wikipedia.org../../../t/o/c/Tocopherol.html"