Vitamin E As Anti Oxidant
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Epidemiological studies have reported an inverse relationship between vitamin E status and coronary heart disease. This relationship has not, however, been confirmed by the majority of intervention studies, which have been carried out relatively late in the disease process. The protective effects of vitamin E may be more important earlier in life, before vascular changes have become established. This study investigated whether dietary vitamin E could prevent preclinical arterial changes in young adults relevant to the development of cardiovascular disease. 19
tocopherol) as protective factor in atherosclerosis in rhesus monkeys. A significant decrease in serum cholesterol and serum triglyceride levels was found in the group of animals which were reverted to stock diet along with vitamin E injections after 9 months of atherogenic diet feeding. Decreases in malonyldialdehyde levels and antioxidant enzyme activities were less significant in animals continued on an atherogenic diet feeding along with vitamin E as compared with animals fed a stock diet with vitamin E supplementation. The overall observations in this study suggest that antioxidant status and lipid peroxidation could be partly restored with vitamin E supplementation in experimental atherosclerosis. Damage to endothelial cells destroys their antithrombotic status and leads to fatal thrombosis. 39
Objectives: The purpose of this study was to conduct a systematic review of the scientific literature to identify and assess the evidence for the efficacy of the antioxidant supplements vitamin C, vitamin E, and coenzyme Q10 for the prevention and treatment of cardiovascular disease or modification of known risk factors for cardiovascular disease. The results may be used to develop a research agenda as well as to assist clinicians in advising patients who desire to take antioxidants to modify their risk of cardiovascular disease. 45
The meta-analysis of 67 randomized studies found that supplemental antioxidants do not reduce mortality and that some — including vitamin A, beta-carotene and vitamin E — could increase mortality. The review combined evidence from more than 200,000 people. 22
Previous studies on the effect of antioxidant vitamins, particularly beta-carotene, on lung function had used dietary intake to estimate antioxidant level and results were inconsistent. This investigation measured blood-serum levels of vitamin C, vitamin E, retinol (a form of vitamin A) and the carotenoids beta-crytoxanthin, lutein/zeaxanthin, beta-carotene and lycopene in 1,616 randomly selected residents of Western New York. 34
Although true vitamin E deficiency is rare, suboptimal intake of vitamin E is relatively common in the U.S. The National Health and Nutrition Examination Survey III (NHANES III) examined the dietary intake and blood levels of alpha-tocopherol in 16,295 multi-ethnic adults over the age of 18. Twenty seven % of white participants, 41% of African Americans, 28% of Mexican Americans and 32% of the other participants were found to have blood levels of alpha-tocopherol less than 20 micromoles/liter, a value chosen because the literature suggests an increased risk for cardiovascular disease below this level (11). 7
Vitamin E can protect against cancer. It has been noted that people with cancer often have lower levels of vitamin E. Plus, studies that observed groups of people over long periods of time suggest that diets rich in antioxidants, including vitamin E, may be connected to a reduced risk of certain types of cancer, such as colon cancer. Supplementation with vitamin E may therefore, reduce your risk of developing this condition. 1
Antioxidants such as vitamin E act to protect your cells against the effects of free radicals, which are potentially damaging by-products of energy metabolism. Free radicals can damage cells and may contribute to the development of cardiovascular disease and cancer. Studies are underway to determine whether vitamin E, through its ability to limit production of free radicals, might help prevent or delay the development of those chronic diseases. Vitamin E has also been shown to play a role in immune function, in DNA repair, and other metabolic processes [2-3]. 2
Eager to monitor vitamin E activity in humans, Dr. Al Tappel at the University of California, Davis, conducted an experiment with athletes. Because the byproducts of oxidative reactions can be measured in exhaled air, the athletes were given breathing monitors as they ran at maximum capacity on treadmills. After a two-week period, oxidation levels in the runners (taking as much as 750 mg of vitamin E per day due to extensive exertion) dropped by an astounding 50 percent. 38
Five large-scale clinical trials published in the 1990s reached differing conclusions about the effect of antioxidants on cancer. The studies examined the effect of beta-carotene and other antioxidants on cancer in different patient groups. However, beta-carotene appeared to have different effects depending upon the patient population. The conclusions of each study are summarized below. 12
A few studies suggest that vitamin E may be helpful in both the treatment (pain relief, increased joint mobility) and prevention (at least in men) of osteoarthritis. Studies comparing vitamin E with diclofenac, a non-steroidal anti-inflammatory drug (NSAID) used to treat osteoarthritis found both to be equally effective. Recent studies showed that you could significantly lower your risk of developing Alzheimer�s disease if you took a combination of vitamin C and E in high doses. There are several reasons why vitamin E might help treat Alzheimer’s disease. The fat-soluble vitamin readily enters the brain and exerts its antioxidative properties. 1
Oxidative stress is believed to contribute to the development of Alzheimer’s disease; therefore, again, it makes at least theoretical sense that antioxidants, like vitamin E, help prevent this condition. Studies have also suggested that vitamin E supplementation improves cognitive performance in healthy individuals and in those with dementia from causes other than Alzheimer’s (for example, multiple strokes). 1
Conclusions: For the combinations and conditions studied, the pooled analysis of smaller studies does not show evidence of an effect of vitamin E alone or in combination with other agents on all-cause mortality, cardiovascular mortality, fatal or nonfatal MI, or blood lipid levels. Results from a number of large clinical trials not included in the pooled analysis were substantially in agreement with this conclusion. Large studies of vitamin C in combination with other antioxidants for the prevention of cardiovascular disease reported no favorable outcomes. There is no convincing evidence either supporting or refuting the value of coenzyme Q10 in cardiovascular disease. 45
A more thorough discussion of the complex issues involved in analyzing the results of recent trials of vitamin E in heart disease can be found in the Fall/Winter 1999 issue of the Linus Pauling Institute Newsletter: Fish Oil, Vitamin E, Genes, Diet, and CHAOS. For a discussion of some of the limitations of the HOPE study see the article, Vitamin E: Hope or Hopeless, in the Spring/Summer 2000 issue of the Linus Pauling Institute Newsletter. 7
It’s a similar story with the world’s most popular antioxidant. Vitamin E shot to fame in the early 1990s, after two large studies involving more than 127,000 people in total found that those with a diet high in vitamin E were significantly less likely to develop cardiovascular disease. The first study followed 87,245 female nurses for eight years; it found that the top 20 per cent with respect to vitamin E consumption had a 41 per cent lower incidence of cardiovascular disease than the bottom 20 per cent (New England Journal of Medicine, vol 328, p 1444). The second study, involving 39,910 male health professionals, found a similar reduction in heart disease risk (New England Journal of Medicine, vol 328, p 1450). 40
References
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