Vitamin E and Health
Many claims have been made about vitamin E’s potential to promote health and prevent and treat disease. The mechanisms by which vitamin E might provide this protection include its function as an antioxidant and its roles in anti-inflammatory processes, inhibition of platelet aggregation, and immune enhancement.
A primary barrier to characterizing the roles of vitamin E in health is the lack of validated biomarkers for vitamin E intake and status to help relate intakes to valid predictors of clinical outcomes . This section focuses on four diseases and disorders in which vitamin E might be involved: heart disease, cancer, eye disorders, and cognitive decline.
Coronary heart disease
Evidence that vitamin E could help prevent or delay coronary heart disease (CHD) comes from several sources. In vitro studies have found that the nutrient inhibits oxidation of low-density lipoprotein (LDL) cholesterol, thought to be a crucial initiating step for atherosclerosis . Vitamin E might also help prevent the formation of blood clots that could lead to a heart attack or venous thromboembolism .
Several observational studies have associated lower rates of heart disease with higher vitamin E intakes. One study of approximately 90,000 nurses found that the incidence of heart disease was 30% to 40% lower in those with the highest intakes of vitamin E, primarily from supplements . Among a group of 5,133 Finnish men and women followed for a mean of 14 years, higher vitamin E intakes from food were associated with decreased mortality from CHD .
However, randomized clinical trials cast doubt on the efficacy of vitamin E supplements to prevent CHD . For example, the Heart Outcomes Prevention Evaluation (HOPE) study, which followed almost 10,000 patients at high risk of heart attack or stroke for 4.5 years , found that participants taking 400 IU/day of natural vitamin E experienced no fewer cardiovascular events or hospitalizations for heart failure or chest pain than participants taking a placebo. In the HOPE-TOO followup study, almost 4,000 of the original participants continued to take vitamin E or placebo for an additional 2.5 years . HOPE-TOO found that vitamin E provided no significant protection against heart attacks, strokes, unstable angina, or deaths from cardiovascular disease or other causes after 7 years of treatment. Participants taking vitamin E, however, were 13% more likely to experience, and 21% more likely to be hospitalized for, heart failure, a statistically significant but unexpected finding not reported in other large studies.
The HOPE and HOPE-TOO trials provide compelling evidence that moderately high doses of vitamin E supplements do not reduce the risk of serious cardiovascular events among men and women >50 years of age with established heart disease or diabetes . These findings are supported by evidence from the Women’s Angiographic Vitamin and Estrogen study, in which 423 postmenopausal women with some degree of coronary stenosis took supplements with 400 IU vitamin E (type not specified) and 500 mg vitamin C twice a day or placebo for >4 years . Not only did the supplements provide no cardiovascular benefits, but all-cause mortality was significantly higher in the women taking the supplements.
The latest published clinical trial of vitamin E’s effects on the heart and blood vessels of women included almost 40,000 healthy women ≥45 years of age who were randomly assigned to receive either 600 IU of natural vitamin E on alternate days or placebo and who were followed for an average of 10 years . The investigators found no significant differences in rates of overall cardiovascular events (combined nonfatal heart attacks, strokes, and cardiovascular deaths) or all-cause mortality between the groups. However, the study did find two positive and significant results for women taking vitamin E: they had a 24% reduction in cardiovascular death rates, and those ≥65 years of age had a 26% decrease in nonfatal heart attack and a 49% decrease in cardiovascular death rates.
The most recent published clinical trial of vitamin E and men’s cardiovascular health included almost 15,000 healthy physicians ≥50 years of age who were randomly assigned to receive 400 IU synthetic alpha-tocopherol every other day, 500 mg vitamin C daily, both vitamins, or placebo . During a mean followup period of 8 years, intake of vitamin E (and/or vitamin C) had no effect on the incidence of major cardiovascular events, myocardial infarction, stroke, or cardiovascular morality. Furthermore, use of vitamin E was associated with a significantly increased risk of hemorrhagic stroke.
In general, clinical trials have not provided evidence that routine use of vitamin E supplements prevents cardiovascular disease or reduces its morbidity and mortality. However, participants in these studies have been largely middle-aged or elderly individuals with demonstrated heart disease or risk factors for heart disease. Some researchers have suggested that understanding the potential utility of vitamin E in preventing CHD might require longer studies in younger participants taking higher doses of the supplement . Further research is needed to determine whether supplemental vitamin E has any protective value for younger, healthier people at no obvious risk of CHD.
Antioxidant nutrients like vitamin E protect cell constituents from the damaging effects of free radicals that, if unchecked, might contribute to cancer development . Vitamin E might also block the formation of carcinogenic nitrosamines formed in the stomach from nitrites in foods and protect against cancer by enhancing immune function . Human trials and surveys that attempted to associate vitamin E intake with cancer incidence have generally been inconclusive.
Some research links higher intakes of vitamin E with a decreased incidence of breast and prostate cancers , but the evidence is inconsistent. For example, an examination of the impact of dietary factors, including vitamin E, on the incidence of postmenopausal breast cancer in >18,000 women found no benefit from the vitamin . Similarly, a prospective cohort study of >29,000 men found no association between dietary or supplemental vitamin E intake and prostate cancer risk, with one exception: among current smokers and men who had quit, vitamin E intakes of more than 400 IU/day were associated with a statistically significant 71% reduction in the risk of advanced prostate cancer . A large randomized clinical trial began in 2001 to determine whether 7-12 years of daily supplementation with synthetic vitamin E (400 IU), with or without selenium (200 mcg), reduces the number of new prostate cancers in healthy men. The trial was discontinued in October 2008 when an analysis found that the supplements, taken alone or together for an average of 5 years, did not prevent prostate cancer . Study staff members will continue to monitor participants’ health for an additional 3 years.
One study of women in Iowa provides evidence that higher intakes of vitamin E from foods and supplements could decrease the risk of colon cancer, especially in women <65 years of age . The overall relative risk for the highest quintile of intake (>35.7 IU/day) compared to the lowest quintile (<5.7 IU/day) was 0.32. However, prospective cohort studies of 87,998 women in the Nurses' Health Study and 47,344 men in the Health Professionals Follow-up Study failed to replicate these results . The American Cancer Society conducted an epidemiologic study examining the association between use of vitamin C and vitamin E supplements and bladder cancer mortality. Of the almost one million adults followed between 1982 and 1998, adults who took supplemental vitamin E for 10 years or longer had a reduced risk of death from bladder cancer ; vitamin C supplementation provided no protection. Both the recently published HOPE-TOO Trial and Women's Health Study evaluated whether vitamin E supplements might protect people from cancer. HOPE-TOO, which followed men and women ≥55 years of age with heart disease or diabetes for 7 years, found no significant differences in the number of new cancers or cancer deaths between the groups taking 400 IU/day vitamin E or a placebo . In the Women's Health Study, in which healthy women ≥45 years of age received either 600 IU vitamin E every other day or a placebo for 10 years, the supplement did not reduce the risk of developing any form of cancer . The inconsistent and limited evidence precludes any recommendations about using vitamin E supplements to prevent cancer. Eye disorders Age-related macular degeneration (AMD) and cataracts are among the most common causes of significant vision loss in older people. Their etiologies are usually unknown, but the cumulative effects of oxidative stress have been postulated to play a role. If so, nutrients with antioxidant functions, such as vitamin E, could be used to prevent or treat these conditions. Prospective cohort studies have found that people with relatively high dietary intakes of vitamin E (e.g., 30 IU/day) have an approximately 20% lower risk of developing AMD than people with low intakes (e.g., <15 IU/day) [34,35]. However, two randomized controlled trials in which participants took supplements of vitamin E (500 IU/day d-alpha-tocopherol in one study  and 111 IU/day dl-alpha-tocopheryl acetate combined with 20 mg/day beta-carotene in the other ) or a placebo failed to show a protective effect for vitamin E on AMD. The Age-Related Eye Disease Study (AREDS), a large randomized clinical trial, revealed that participants with early-stage AMD could slow the progression of their disease by taking a daily supplement of vitamin E (400 IU dl-alpha-tocopheryl acetate), vitamin C (500 mg), beta-carotene (15 mg), zinc (80 mg), and copper (2 mg) for an average of 6.3 years compared to participants taking a placebo . Several observational studies have revealed a potential relationship between vitamin E supplements and the risk of cataract formation. One prospective cohort study found that lens clarity was superior in participants who took vitamin E supplements and those with higher blood levels of the vitamin . In another study, long-term use of vitamin E supplements was associated with slower progression of age-related lens opacification . However, in the randomized AREDS study, the use of the vitamin E-containing supplement package had no apparent effect on the development or progression of cataracts over 7 years . Overall, the available evidence is inconsistent with respect to whether vitamin E supplements, taken alone or in combination with other antioxidants, can reduce the risk of developing AMD or cataracts. However, the formulation of vitamin E, other antioxidants, zinc, and copper used in AREDS holds promise for slowing the progression of AMD in people with early-stage disease. Additional information about the dietary supplements used in AREDS is available at http://www.nei.nih.gov/amd. AREDS 2, a followup study, will determine whether a modified combination of dietary supplements can further slow the progression of vision loss from AMD; further information is available at http://www.nei.nih.gov/areds2. Cognitive decline The brain has a high oxygen consumption rate and abundant polyunsaturated fatty acids in the neuronal cell membranes. Researchers hypothesize that if cumulative free-radical damage to neurons over time contributes to cognitive decline and neurodegenerative diseases, such as Alzheimer's disease, then ingestion of sufficient or supplemental antioxidants (such as vitamin E) might provide some protection . This hypothesis was supported by the results of a clinical trial in 341 patients with Alzheimer's disease of moderate severity who were randomly assigned to receive a placebo, vitamin E (2,000 IU/day dl-alpha-tocopherol), a monoamine oxidase inhibitor (selegiline), or vitamin E and selegiline . Over 2 years, treatment with vitamin E and selegiline, separately or together, significantly delayed functional deterioration and the need for institutionalization compared to placebo. However, participants taking vitamin E experienced significantly more falls. Vitamin E consumption from foods or supplements was associated with less cognitive decline over 3 years in a prospective cohort study of elderly, free-living individuals aged 65-102 years . However, a clinical trial in primarily healthy older women who were randomly assigned to receive 600 IU d-alpha-tocopherol every other day or a placebo for ≤4 years found that the supplements provided no apparent cognitive benefits . Another trial in which 769 men and women with mild cognitive impairment were randomly assigned to receive 2,000 IU/day vitamin E (type not specified), a cholinesterase inhibitor (donepezil), or placebo found no significant differences in the progression rate of Alzheimer’s disease between the vitamin E and placebo groups  In summary, most research results do not support the use of vitamin E supplements by healthy or mildly impaired individuals to maintain cognitive performance or slow its decline with normal aging . More research is needed to identify the role of vitamin E, if any, in the management of cognitive impairment . Health Risks from Excessive Vitamin E Research has not found any adverse effects from consuming vitamin E in food . However, high doses of alpha-tocopherol supplements can cause hemorrhage and interrupt blood coagulation in animals, and in vitro data suggest that high doses inhibit platelet aggregation. Two clinical trials have found an increased risk of hemorrhagic stroke in participants taking alpha-tocopherol; one trial included Finnish male smokers who consumed 50 mg/day for an average of 6 years  and the other trial involved a large group of male physicians in the United States who consumed 400 IU every other day for 8 years . Because the majority of physicians in the latter study were also taking aspirin, this finding could indicate that vitamin E has a tendency to cause bleeding. The FNB has established ULs for vitamin E based on the potential for hemorrhagic effects (see Table 3). The ULs apply to all forms of supplemental alpha-tocopherol, including the eight stereoisomers present in synthetic vitamin E. Doses of up to 1,000 mg/day (1,500 IU/day of the natural form or 1,100 IU/day of the synthetic form) in adults appear to be safe, although the data are limited and based on small groups of people taking at least 2,000 IU for a few weeks or months. Long-term intakes above the UL increase the risk of adverse health effects . Vitamin E ULs for infants have not been established. Table 3: Tolerable Upper Intake Levels (ULs) for Vitamin E  Age Male Female Pregnancy Lactation 1-3 years 200 mg (300 IU) 200 mg (300 IU) 4-8 years 300 mg (450 IU) 300 mg (450 IU) 9-13 years 600 mg (900 IU) 600 mg (900 IU) 14-18 years 800 mg (1,200 IU) 800 mg (1,200 IU) 800 mg (1,200 IU) 800 mg (1,200 IU) 19+ years 1,000 mg (1,500 IU) 1,000 mg (1,500 IU) 1,000 mg (1,500 IU) 1,000 mg (1,500 IU) Two meta-analyses of randomized trials have raised questions about the safety of large doses of vitamin E, including doses lower than the UL. These meta-analyses linked supplementation to small but statistically significant increases in all-cause mortality. One analysis found an increased risk of death at doses of ≥400 IU/day, although the risk began to increase at 150 IU . In the other analysis of studies of antioxidant supplements for disease prevention, the highest quality trials revealed that vitamin E, administered singly (dose range 10 IU-5,000 IU/day; mean 569 IU) or combined with up to four other antioxidants, significantly increased mortality risk . The implications of these analyses for the potential adverse effects of high-dose vitamin E supplements are unclear [51-54]. Participants in the studies included in these analyses were typically middle-aged or older and had chronic diseases or related risk factors. These participants often consumed other supplements in addition to vitamin E. Some of the studies analyzed took place in developing countries in which nutritional deficiencies are common. A review of the subset of studies in which vitamin E supplements were given to healthy individuals for the primary prevention of chronic disease found no convincing evidence that the supplements increased mortality . ============================================================================================================================================================================ Aye apareción en el Blog Natudelia una entrada sobre la Vitamina E....... como no han publicado mi respuesta, pongo esto aquí.... Lo ha puesto porque es un ejemplo muy bueno ( en mi opinión) de lo que es la diferencia entre lo que podriamos llamar - sentido común- y ciencia...... Todo el mundo "sabe" que el poceso de envejecimiento, enfermar, se debe a la oxidación, a los radicales libres..... por tanto los antiidanes son lo "mejor" para la salud........ Pues no necesariamente...... lo de los radicales libres y la oxidación es solo una teoria, no sabemos si es cierto o no. Que los antioxidanes tengan un efecto beneficoso para la salud es todavia menos cierto y como se ve en los estudios que se mencionan arriba, los antioxidantes, particularmente la vitamina E, y tambien la vitamina C son peligrosos para la salud en las dosis que frecuentemente encontramos en los suplementos...... Lo puesto arriba es copiado del National Institutes of Health.