Antioxidants can cancel out the cell-damaging effects of free radicals, and people who eat fruits and vegetables rich in polyphenols and anthocyanins have a lower risk of cancer, heart disease and some neurological diseases This observation suggested that these compounds might prevent conditions such as macular degeneration suppressed immunity due to poor nutrition and neurodegeneration, which are caused by oxidative stress However, despite the clear role of oxidative stress in cardiovascular disease, controlled studies using antioxidant vitamins have observed no reduction in either the risk of developing heart disease, or the rate of progression of existing disease This suggests that other substances in fruit and vegetables (possibly flavonoids) at least partially explain the better cardiovascular health of those who consume more fruit and vegetables
It is thought that oxidation of low density lipoprotein in the blood contributes to heart disease, and initial observational studies found that people taking Vitamin E supplements had a lower risk of developing heart disease.Consequently, at least seven large clinical trials were conducted to test the effects of antioxidant supplement with Vitamin E, in doses ranging from 50 to 600 mg per day. However, none of these trials found a statistically significant effect of Vitamin E on overall number of deaths or on deaths due to heart disease It is not clear if the doses used in these trials or in most dietary supplements are capable of producing any significant decrease in oxidative stress
While several trials have investigated supplements with high doses of antioxidants, the "Supplémentation en Vitamines et Mineraux Antioxydants" (SU.VI.MAX) study tested the effect of supplementation with doses comparable to those in a healthy diet Over 12,500 French men and women took either low-dose antioxidants (120 mg of ascorbic acid, 30 mg of vitamin E, 6 mg of beta carotene, 100 μg of selenium, and 20 mg of zinc) or placebo pills for an average of 7.5 years. The investigators found there was no statistically significant effect of the antioxidants on overall survival, cancer, or heart disease. However, a subgroup analysis showed a 31% reduction in the risk of cancer in men, but not women.
Many nutraceutical and health food companies now sell formulations of antioxidants as dietary supplements and these are widely used in industrialized countries These supplements may include specific antioxidant chemicals, like resveratrol (from grape seeds), combinations of antioxidants, like the "ACES" products that contain beta carotene (provitamin A), vitamin C, vitamin E and Selenium, or herbs that contain antioxidants - such as green tea and jiaogulan. Although some levels of antioxidant vitamins and minerals in the diet are required for good health, there is considerable doubt as to whether antioxidant supplementation is beneficial, and if so, which antioxidant(s) are beneficial and in what amounts.]
It has been suggested that moderate levels of oxidative stress may increase life expectancy of in the worm Caenorhabditis elegans, by inducing a protective response to increased levels of reactive oxygen species However, the suggestion that increased life expectancy comes from increased oxidative stress conflicts with results seen in the yeast Saccharomyces cerevisiae and the situation in mammals is even less clear.
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