Misplaced Pages

#802197

70-511: 1OIP , 1OIZ , 1R5L 7274 50500 ENSG00000137561 ENSMUSG00000073988 P49638 Q8BWP5 NM_000370 NM_015767 NM_001317723 NP_000361 NP_001304652 NP_056582 Alpha- tocopherol transfer protein (α-TTP) is a protein that in humans is encoded by the TTPA gene . This article on a gene on human chromosome 8 is a stub . You can help Misplaced Pages by expanding it . Tocopherol α-Tocopherol

140-435: A Tolerable upper intake level (UL) at 1,000 mg (1,500 IU) per day derived from animal models that demonstrated bleeding at high doses. The European Food Safety Authority reviewed the same safety question and set a UL at 300 mg/day. A meta-analysis of long-term clinical trials reported a non-significant 2% increase in all-cause mortality when α-tocopherol was the only supplement used. Another meta-analysis reported

210-441: A hydrogen atom to reduce free radicals and a hydrophobic side chain that allows for penetration into biological membranes . Both the tocopherols and tocotrienols occur in α (alpha), β (beta), γ (gamma), and δ (delta) forms, determined by the number and position of methyl groups on the chromanol ring. The tocotrienols have the same methyl structure at the ring and the same Greek letter-methyl-notation, but differ from

280-417: A cause and effect relationship has been established between the dietary intake of vitamin E and maintenance of normal cardiac function or of normal blood circulation. Antioxidant vitamins as dietary supplements have been proposed as having benefits if consumed during pregnancy. For the combination of vitamin E with vitamin C supplemented to pregnant women, a Cochrane review of 21 clinical trials concluded that

350-410: A conclusion that the anti-oxidant combination significantly slowed progression. However, because there was no group in the trial receiving only vitamin E, no conclusions could be drawn as to the contribution of the vitamin to the effect. Proponents of megavitamin therapy and orthomolecular medicine advocate natural tocopherols. Meanwhile, clinical trials have largely concentrated on use of either

420-415: A diet low in vitamin E. Vitamin E deficiency causes neurological problems due to poor nerve conduction. These include neuromuscular problems such as spinocerebellar ataxia and myopathies . Deficiency also may cause anemia , due to oxidative damage to red blood cells. Commercial vitamin E supplements may be classified into several distinct categories: Synthetic vitamin E derived from petroleum products

490-419: A different biological activity . In general, the unnatural l-isomers of tocotrienols lack almost all vitamin activity, and half of the possible 8 isomers of the tocopherols (those with 2S chirality at the ring-tail junction) also lack vitamin activity. Of the stereoisomers that retain activity, increasing methylation, especially full methylation to the alpha-form, increases vitamin activity. In tocopherols, this

560-501: A different spatial arrangement of atoms around the central atom. A molecule having multiple stereocenters will produce many possible stereoisomers. In compounds whose stereoisomerism is due to tetrahedral (sp ) stereogenic centers, the total number of hypothetically possible stereoisomers will not exceed 2 , where n is the number of tetrahedral stereocenters. However, this is an upper bound because molecules with symmetry frequently have fewer stereoisomers. The stereoisomers produced by

630-405: A disease, may be considered suggestive, but any conclusions also should rest on randomized clinical trials of sufficient size and duration to measure clinically significant results. One concern with correlations is that other nutrients and non-nutrient compounds (such as polyphenols) may be higher in the same diets that are higher in vitamin E. Another concern for the relevance of RCTs described below

700-533: A food composition database. The last major revision was Release 28, September 2015. In general, food sources with the highest concentrations of vitamin E are vegetable oils , followed by nuts and seeds . Adjusting for typical portion sizes, however, for many people in the United States the most important sources of vitamin E include fortified breakfast cereals . Vitamin E deficiency is rare, and in almost all instances caused by an underlying disease rather than

770-485: A location (point) within a molecule, rather than a particular atom, in which the interchanging of two groups creates a stereoisomer. A stereocenter can have either four different attachment groups, or three different attachment groups where one group is connected by a double bond. Since stereocenters can exist on achiral molecules, stereocenters can have either sp or sp hybridization . Stereoisomers are compounds that are identical in composition and connectivity but have

SECTION 10

#1732869376803

840-472: A mixture of toluene and 2,3,5-trimethyl-hydroquinone that reacts with isophytol to all-rac-α-tocopherol, using iron in the presence of hydrogen chloride gas as a catalyst. The reaction mixture obtained is filtered and extracted with aqueous caustic soda. Toluene is removed by evaporation and the residue (all rac-α-tocopherol) is purified by vacuum distillation." Specification for the ingredient is >97% pure. This synthetic dl-α-tocopherol has approximately 50% of

910-500: A non-significant 1% increase in all-cause mortality when α-tocopherol was the only supplement. Subset analysis reported no difference between natural (plant extracted) or synthetic α-tocopherol, or whether the amount used was less than or more than 400 IU/day. There are reports of vitamin E-induced allergic contact dermatitis from use of vitamin-E derivatives such as tocopheryl linoleate and tocopherol acetate in skin care products. Incidence

980-470: A process of reviewing and approving food and dietary supplement health claims in 1993. A Qualified Health Claim issued in 2012 allows product label claims that vitamin E may reduce risk of renal, bladder, and colorectal cancers, with a stipulation that the label must include a mandatory qualifier sentence: “FDA has concluded that there is very little scientific evidence for this claim.” The European Food Safety Authority (EFSA) reviews proposed health claims for

1050-498: A propeller-type structure, with two different enantiomers denoted Λ and Δ. As mentioned earlier, the requirement for an atom to be a chirality center is that the atom must be sp hybridized with four different attachments. Because of this, all chirality centers are stereocenters. However, only under some conditions is the reverse true. Recall that a point can be considered a sterocenter with a minimum of three attachment points; stereocenters can be either sp or sp hybridized, as long as

1120-472: A statistically significant reduction in risk. In male tobacco smokers, 50 mg/day reduced prostate cancer risk by 32%, but in a different trial, majority non-smokers, 400 IU/day increased risk by 17%. In women who consumed either placebo or 600 IU of natural-source vitamin E on alternate days for an average of 10.1 years there were no significant differences for breast cancer , lung cancer, or colon cancer. The U.S. Food and Drug Administration initiated

1190-439: A stereocenter if all three groups attached are different because the electron pair of the amine functions as a fourth group. However, nitrogen inversion , a form of pyramidal inversion , causes racemization which means that both epimers at that nitrogen are present under normal circumstances. Racemization by nitrogen inversion may be restricted (such as quaternary ammonium or phosphonium cations), or slow, which allows

1260-401: A stereoisomeric carbon only at the 2' ring-tail position). The four tocotrienols (in order of decreasing methylation: d-α-, d-β-, d-γ-, and d-δ-tocotrienol) 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 (the phytyl tail of tocopherols gives

1330-588: A synthetic, all-racemic d-α-tocopheryl acetate or synthetic dl-α-tocopheryl acetate. Tocopherol is described as functioning as an antioxidant. A dose-ranging trial was conducted in people with chronic oxidative stress attributed to elevated serum cholesterol. Plasma F2-isoprostane concentration was selected as a biomarker of free radical-mediated lipid peroxidation. Only the two highest doses - 1600 and 3200 IU/day - significantly lowered F2-isoprostane. Alzheimer's disease (AD) and vascular dementia are common causes of decline of brain functions that occur with age. AD

1400-467: Is 15 mg/day. The RDA is based on the α-tocopherol form because it is the most active form as originally tested. Vitamin E supplements are absorbed best when taken with meals. The U.S. Institute of Medicine has set an upper tolerable intake level (UL) for vitamin E at 1,000 mg (1,500 IU) per day. The European Food Safety Authority sets UL at 300 mg α-tocopherol equivalents /day. For dietary purposes, vitamin E activity of vitamin E isomers

1470-493: Is a chiral molecule. The eight stereoisomers of α-tocopherol differ in the arrangement of groups around these stereocenters. In the image of RRR -α-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 -α-tocopherol. These stereoisomers also may be named in an alternative older nomenclature, where

SECTION 20

#1732869376803

1540-442: Is a chronic neurodegenerative disease that worsens over time. The disease process is associated with plaques and tangles in the brain. Vascular dementia may be caused by ischemic or hemorrhagic infarcts affecting multiple brain areas, including the anterior cerebral artery territory, the parietal lobes , or the cingulate gyrus . Both types of dementia may be present. Vitamin E status (and that of other antioxidant nutrients)

1610-428: Is a type of stereocenter. A chirality center is defined as an atom holding a set of four different ligands (atoms or groups of atoms) in a spatial arrangement which is non-superposable on its mirror image. Chirality centers must be sp hybridized, meaning that a chirality center can only have single bonds . In organic chemistry , a chirality center usually refers to a carbon , phosphorus , or sulfur atom, though it

1680-447: Is also possible for other atoms to be chirality centers, especially in areas of organometallic and inorganic chemistry . The concept of a chirality center generalizes the concept of an asymmetric carbon atom (a carbon atom bonded to four different entities) to a broader definition of any atom with four different attachment groups in which an interchanging of any two attachment groups gives rise to an enantiomer . A carbon atom that

1750-423: Is attached to four different substituent groups is called an asymmetric carbon atom or chiral carbon . Chiral carbons are the most common type of chirality center. Chirality is not limited to carbon atoms, though carbon atoms are often centers of chirality due to their ubiquity in organic chemistry. Nitrogen and phosphorus atoms can also form bonds in a tetrahedral configuration. A nitrogen in an amine may be

1820-451: Is conjectured as having a possible impact on risk of Alzheimer's disease and vascular dementia. A review of dietary intake studies reported that higher consumption of vitamin E from foods lowered the risk of developing AD by 24%. A second review examined serum vitamin E levels and reported lower serum vitamin E in AD patients compared to healthy, age-matched people. In 2017 a consensus statement from

1890-463: Is due to the higher binding energy of the α-tocopherol form of the vitamin to the tocopherol binding protein. As a food additive , tocopherol is labeled with these E numbers : E306 (tocopherol), E307 (α-tocopherol), E308 (γ-tocopherol), and E309 (δ-tocopherol). All of these are approved in the US, EU, and Australia and New Zealand for use as antioxidants. α-Tocopherol is the form of vitamin E that

1960-589: Is expressed as α-tocopherol equivalents (a-TEs). One a-TE is defined by the biological activity of 1 mg (natural) d-α-tocopherol in the resorption-gestation test. According to listings by FAO and others β-tocopherol should be multiplied by 0.5, γ-tocopherol by 0.1, and α-tocotrienol by 0.3. The IU is converted to aTE by multiplying it with 0.67. These factors do not correlate with the antioxidant activity of vitamin E isomers, where tocotrienols show even much higher activity in vivo. The U.S. Department of Agriculture (USDA), Agricultural Research Services, maintains

2030-616: Is low despite widespread use. The amounts of α-tocopherol, other tocopherols and tocotrienols that are components of dietary vitamin E, when consumed from foods, do not appear to cause any interactions with drugs. Consumption of α-tocopherol as a dietary supplement in amounts in excess of 300 mg/day may lead to interactions with aspirin , warfarin , tamoxifen , and cyclosporine A in ways that alter function. For aspirin and warfarin, high amounts of vitamin E may potentiate anti-blood clotting action. One small trial demonstrated that vitamin E at 400 mg/day reduced blood concentration of

2100-485: Is manufactured as all- racemic α-tocopheryl acetate with a mixture of eight stereoisomers. In this mixture, one α-tocopherol molecule in eight molecules are in the form of RRR -α-tocopherol (12.5% of the total). 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) dl,dl,dl-tocopherol. The present largest manufacturers of this type are DSM and BASF . Natural α-tocopherol

2170-545: Is more precisely dl,dl,dl-α-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". Tocotrienols also belong to the vitamin E family. Tocotrienols have four natural 2' d-isomers (they have

Alpha-tocopherol transfer protein - Misplaced Pages Continue

2240-627: Is preferentially absorbed and accumulated in humans. 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 α-tocopherol. Although the mono-methylated form ddd-γ-tocopherol is the most prevalent form of vitamin E in oils, there is evidence that rats can methylate this form to the preferred α-tocopherol, since several generations of rats retained α-tocopherol tissue levels, even when those generations were fed only γ-tocopherol through their lives. There are three stereocenters in α-tocopherol, so this

2310-461: Is some supporting evidence from randomized clinical trials (RCTs). A meta-analysis on the effects of α-tocopherol supplementation in RCTs on aspects of cardiovascular health reported that when consumed without any other antioxidant nutrient, the relative risk of heart attack was reduced by 18%. The results were not consistent for all of the individual trials incorporated into the meta-analysis. For example,

2380-465: Is that while observational studies are comparing disease risk between low and high dietary intake of naturally occurring vitamin E from food (when worldwide, the adult median dietary intake is 6.2 mg/d for d-α-tocopherol; 10.2 mg/day when all of the tocopherol and tocotrienol isomers are included), the prospective RCTs often used 400 IU/day of synthetic dl-α-tocopherol as the test product, equivalent to 268 mg of α-tocopherol equivalents. In

2450-606: Is the RRR-α (or ddd-α) form. The synthetic dl,dl,dl-α ("dl-α") form is not so active as the natural ddd-α ("d-α") tocopherol form. This is mainly due to reduced vitamin activity of the four possible stereoisomers that 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). The three unnatural "2R" stereoisomers with natural R configuration at this 2' stereocenter, but S at one of

2520-505: Is the main source found in supplements and in the European diet, where the main dietary sources are olive and sunflower oils, while γ-tocopherol is the most common form in the American diet due to a higher intake of soybean and corn oil. Vitamin E exists in eight different forms, four tocopherols and four tocotrienols . All feature a chromane ring, with a hydroxyl group that can donate

2590-484: The European Union countries. As of March 2018, EFSA has not evaluated any vitamin E and cancer prevention claims. A meta-analysis from 2015 reported that for studies that reported serum tocopherol, higher serum concentration was associated with a 23% reduction in relative risk of age-related cataracts (ARC), with the effect due to differences in nuclear cataract rather than cortical or posterior subcapsular cataract -

2660-419: The peroxyl radical and other free radicals , minimizing their damaging effect. The thus generated tocopheryl radical is relatively unreactive, but reverts to tocopherol by a redox reaction with a hydrogen donor such as vitamin C . As they are fat-soluble, tocopherols are incorporated into cell membranes, which are thus protected from oxidative damage. The U.S. Recommended Dietary Allowance (RDA) for adults

2730-534: The British Association for Psychopharmacology included that until further information is available, vitamin E cannot be recommended for treatment or prevention of Alzheimer's disease. From reviews of observational studies, diets higher in vitamin E content were associated with a lower relative risk of kidney cancer , bladder cancer , and lung cancer When comparisons were made between the lowest and highest groups for dietary vitamin E consumption from food,

2800-515: The Physicians' Health Study II did not show any benefit after 400 IU every other day for eight years, for heart attack, stroke, coronary mortality, or all-cause mortality. The effects of vitamin E supplementation on incidence of stroke were summarized in 2011. There were no significant benefits for vitamin E versus placebo for risk of stroke, or for subset analysis for ischaemic stroke , haemorrhagic stroke , fatal stroke, or non-fatal stroke. In 2001

2870-515: The U.S. Food and Drug Administration rejected proposed health claims for vitamin E and cardiovascular health. The U.S. National Institutes of Health also reviewed the literature and concluded there was not sufficient evidence to support the idea that routine use of vitamin E supplements prevents cardiovascular disease or reduces its morbidity and mortality. In 2010 the European Food Safety Authority reviewed and rejected claims that

Alpha-tocopherol transfer protein - Misplaced Pages Continue

2940-495: The US, the popularity for vitamin E as a dietary supplement may have peaked around 2000. The Nurses' Health Study (NHS) and the Health Professionals Follow-up Study (HPFS) tracked dietary supplement use by people over the age of 40 during years 1986–2006. For women, user prevalence was 16.1% in 1986, 46.2% in 1998, 44.3% in 2002, but had decreased to 19.8% in 2006. Similarly, for men, prevalence for same years

3010-816: The USA contain at least 20% w/w other natural R, R,R- tocopherols, i.e. R, R,R-α-tocopherol content plus at least 25% R, R,R-β-, R, R,R-γ-, R, R,R-δ-tocopherols. Some brands may contain 20.0% w/w or more of the other tocopherols and measurable tocotrienols. Some mixed tocopherols with higher γ-tocopherol content are marketed as "High Gamma-Tocopherol". The label should report each component in milligrams, except R, R,R-α-tocopherol may still be reported in IU. Mixed tocopherols also may be found in other nutritional supplements. Observational studies that measure dietary intake and/or serum concentration, and experimental studies that ideally are randomized clinical trials (RCTs), are two means of examining

3080-527: The USA documented a 50% decrease between 2000 and 2006, with a significant cause attributed to a well-publicized meta-analysis that had concluded that high-dosage vitamin E increased all-cause mortality. A Cochrane review published in 2017 (updated in 2023) on antioxidant vitamin and mineral supplements for slowing the progression of age-related macular degeneration (AMD) identified only one vitamin E clinical trial. That trial compared 500 IU/day of α-tocopherol to placebo for four years and reported no effect on

3150-427: The analogous tocopherols by the presence of three double bonds in the hydrophobic side chain. The unsaturation of the tails gives tocotrienols only a single stereoisomeric carbon (and thus two possible isomers per structural formula, one of which occurs naturally), whereas tocopherols have three centers (and eight possible stereoisomers per structural formula, again, only one of which occurs naturally). Each form has

3220-555: The anti-breast cancer drug tamoxifen. In multiple clinical trials, vitamin E lowered blood concentration of the immuno-suppressant drug, cyclosporine A. The U.S. National Institutes of Health, Office of Dietary Supplements, raises a concern that co-administration of vitamin E could counter the mechanisms of anti-cancer radiation therapy and some types of chemotherapy, and so advises against its use in these patient populations. The references it cited reported instances of reduced treatment adverse effects, but also poorer cancer survival, raising

3290-400: The arrangement of atoms around a stereocenter. The Cahn-Ingold-Prelog (CIP) system uses R and S designations to define the configuration of atoms about any stereocenter. A designation of R denotes a clockwise direction of substituent priority around the stereocenter, while a designation of S denotes a counter-clockwise direction of substituent priority. A chirality center (chiral center)

3360-551: The average reductions in relative risk were in the range of 16-19%. For all of these reviews, the authors noted that the findings needed to be confirmed by prospective studies. From randomized clinical trials (RCTs) in which α-tocopherol was administered as a dietary supplement, results differed from the dietary intake reviews. A RCT of 400 IU/day of α-tocopherol did not reduce risk of bladder cancer. In male tobacco smokers, 50 mg/day had no impact on developing lung cancer. A review of RCTs for colorectal cancer reported lack of

3430-581: The consumption of foods high in vitamin E, and also higher serum concentration of α-tocopherol. In one of the largest observational studies, almost 90,000 healthy nurses were tracked for eight years. Compared to those in the lowest fifth for reported vitamin E consumption (from food and dietary supplements), those in the highest fifth were at a 34% lower risk of major coronary disease. Diet higher in vitamin E also may be higher in other, unidentified components that promote heart health, or people choosing such diets may be making other healthy lifestyle choices. There

3500-430: The data do not support vitamin E supplementation - majority of trials α-tocopherol at 400 IU/day plus vitamin C at 1000 mg/day - as being efficacious for reducing risk of stillbirth , neonatal death , preterm birth , preeclampsia , or any other maternal or infant outcomes, either in healthy women or those considered at risk for pregnancy complications. The review identified only three small trials in which vitamin E

3570-414: The effects or lack thereof of a proposed intervention on human health. Healthcare outcomes may be expected to be in accord between reviews of observational and experimental studies. If there is a lack of agreement, then factors other than design need to be considered. In observational studies on vitamin E, an inverse correlation between dietary intake and risk of a disease, or serum concentration and risk of

SECTION 50

#1732869376803

3640-401: The existence of chirality. Metal atoms with tetrahedral or octahedral geometries may also be chiral due to having different ligands. For the octahedral case, several chiralities are possible. Having three ligands of two types, the ligands may be lined up along the meridian, giving the mer -isomer, or forming a face—the fac isomer. Having three bidentate ligands of only one type gives

3710-466: The number of tetrahedral stereocenters; however, exceptions such as meso compounds can reduce the prediction to below the expected 2 . Chirality centers are a type of stereocenter with four different substituent groups; chirality centers are a specific subset of stereocenters because they can only have sp hybridization, meaning that they can only have single bonds . Stereocenters can exist on chiral or achiral molecules. They are defined as

3780-401: The number of stereoisomers to below the hypothetical 2 amount due to symmetry. Additionally, certain configurations may not exist due to steric reasons. Cyclic compounds with chiral centers may not exhibit chirality due to the presence of a two-fold rotation axis. Planar chirality may also provide for chirality without having an actual chiral center present. Configuration is defined as

3850-430: The other centers in the tail (i.e., RSR, RRS, RSS), appear to retain substantial RRR vitamin activity, because they are recognized by the alpha-tocopherol transfer protein , and thus maintained in the plasma, where the other four stereoisomers (SRR, SRS, SSR, and SSS) are not. Thus, the synthetic all-rac-α-tocopherol, in theory, would have approximately half the vitamin activity of RRR-α-tocopherol in humans. Experimentally,

3920-458: The possibility for 2 more stereoisomeric sites in these molecules that tocotrienols do not have). Tocotrienols has seen less research as compared to tocopherols. Tocopherols are radical scavengers, delivering an H atom to quench free radicals. At 323 kJ/mol, the O-H bond in tocopherols is approximately 10% weaker than in most other phenols . This weak bond allows the vitamin to donate a hydrogen atom to

3990-418: The possibility of tumor protection from the oxidative damage intended by the treatments. Naturally sourced d-α-tocopherol can be extracted and purified from seed oils, or γ-tocopherol can be extracted, purified, and methylated to create d-alpha-tocopherol. In contrast to α-tocopherol extracted from plants, which also is called d-α-tocopherol, industrial synthesis creates dl-α-tocopherol. "It is synthesized from

4060-554: The potency of d-α-tocopherol. Manufacturers of dietary supplements and fortified foods for humans or domesticated animals convert the phenol form of the vitamin to an ester using either acetic acid or succinic acid because the esters are more chemically stable, providing for a longer shelf-life. The ester forms are de-esterified in the gut and absorbed as free α-tocopherol. During feeding experiments with rats Herbert McLean Evans concluded in 1922 that besides vitamins B and C, an unknown vitamin existed. Although every other nutrition

4130-550: The presence of multiple stereocenters can be defined as enantiomers (non-superposable mirror images) and diastereomers (non-superposable, non-identical, non-mirror image molecules). Enantiomers and diastereomers are produced due to differing stereochemical configurations of molecules containing the same composition and connectivity (bonding); the molecules must have multiple (two or more) stereocenters to be classified as enantiomers or diastereomers. Enantiomers and diastereomers will produce individual stereoisomers that contribute to

4200-468: The progression of AMD in people already diagnosed with the condition. Another Cochrane review, same year, same authors, reviewed the literature on α-tocopherol preventing the development of AMD. This review identified four trials, duration 4–10 years, and reported no change to risk of developing AMD. A large clinical trial known as AREDS compared β-carotene (15 mg), vitamin C (500 mg), and α-tocopherol (400 IU) to placebo for up to ten years, with

4270-410: The ratio of activities of the 8 stereoisomer racemic mixture to the natural vitamin, is 1 to 1.36 in the rat pregnancy model (suggesting a measured activity ratio of 1/1.36 = 74% of natural, for the 8-isomer racemic mix). Although it is clear that mixtures of stereoisomers are not so active as the natural RRR -α-tocopherol form, in the ratios discussed above, specific information on any side effects of

SECTION 60

#1732869376803

4340-551: The seven synthetic vitamin E stereoisomers is not readily available. 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. α-Tocopheryl esters are de-esterified in the gut and then absorbed as the free tocopherol. Tocopheryl nicotinate , tocopheryl linolate , and tocopheryl palmitate esters are also used in cosmetics and some pharmaceuticals. "Mixed tocopherols" in

4410-506: The stereocenter, interchanging any two different groups creates a new stereoisomer . Stereocenters are also referred to as stereogenic centers . A stereocenter is geometrically defined as a point (location) in a molecule; a stereocenter is usually but not always a specific atom, often carbon. Stereocenters can exist on chiral or achiral molecules; stereocenters can contain single bonds or double bonds. The number of hypothetical stereoisomers can be predicted by using 2 , with n being

4480-418: The stereocenters are either in the d or l form. 1 IU of tocopherol is defined as ⅔ milligrams of RRR -α-tocopherol (formerly named d-α-tocopherol or sometimes ddd-α-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 -α-tocopheryl acetate . This mix of stereoisomers is often called dl-α-tocopheryl acetate, even though it

4550-432: The three major classifications of age-related cataracts. However, this article and a second meta-analysis reporting on clinical trials of α-tocopherol supplementation reported no statistically significant change to risk of ARC when compared to placebo. Research on the effects of vitamin E on cardiovascular disease has produced conflicting results. An inverse relation has been observed between coronary heart disease and

4620-419: The total number of possible stereoisomers. However, the stereoisomers produced may also give a meso compound , which is an achiral compound that is superposable on its mirror image; the presence of a meso compound will reduce the number of possible stereoisomers. Since a meso compound is superposable on its mirror image, the two "stereoisomers" are actually identical. Resultantly, a meso compound will reduce

4690-404: The vitamin was given its name by Evans from Greek words meaning "to bear young" with the addition of the -ol as an alcohol. The structure was determined shortly thereafter in 1938. Stereocenter In stereochemistry , a stereocenter of a molecule is an atom (center), axis or plane that is the focus of stereoisomerism ; that is, when having at least three different groups bound to

4760-615: Was 18.9%, 52.0%, 49.4%, and 24.5%. The authors theorized that declining use in these health science aware populations may have been due to publications of studies that showed either no benefits or negative consequences from vitamin E supplements. There is other evidence for declining use of vitamin E. Within the U.S. military services, vitamin prescriptions written for active, reserve and retired military, and their dependents, were tracked over years 2007–2011. Vitamin E prescriptions decreased by 53% while vitamin C remained constant and vitamin D increased by 454%. A report on vitamin E sales volume in

4830-414: 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 C 29 H 50 O 2 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,

4900-409: Was supplemented without co-supplementation with vitamin C. None of these trials reported any clinically meaningful information. Although there is widespread use of vitamin E as a topical medication , with claims for improved wound healing and reduced scar tissue, reviews have repeatedly concluded that there is insufficient evidence to support these claims. The U.S. Food and Nutrition Board set

#802197