The use of antioxidants to prevent disease is controversial. In a high-risk group like smokers, high doses of beta carotene increased the rate of lung cancer. In less high-risk groups, the use of vitamin E appears to reduce the risk of heart disease. In other diseases, such as Alzheimer's, the evidence on vitamin E supplementation is mixed. Since dietary sources contain a wider range of carotenoids and vitamin E tocopherols and tocotrienols from whole foods, ex post facto epidemiological studies can have differing conclusions than artificial experiments using isolated compounds. However, AstraZeneca's radical scavenging nitrone drug NXY-059 shows some efficacy in the treatment of stroke.
Oxidative stress (as formulated in Harman's free radical theory of aging) is also thought to contribute to the aging process. While there is good evidence to support this idea in model organisms such as ''Drosophila melanogaster'' and ''Caenorhabditis elegans'', recent evidence from Michael Ristow's laboratory suggests that oxidative stress may also promote life expectancy of Caenorhabditis elegans by inducing a secondary response to initially increased levels of reactive oxygen species. This process was previously named mitohormesis or mitochondrial hormesis on a purely hypothetical basis. The situation in mammals is even less clear. Recent epidemiological findings support the process of mitohormesis, and even suggest that antioxidants may increase disease prevalence in humans (although the results were influenced by studies on smokers).
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