Age-related macular degeneration and cataracts are leading causes of vision loss among aging individuals worldwide. Observational studies have found that lens opacity, an early sign of cataract formation, was lessened in subjects who took vitamin E supplements regularly.109 Under conditions of oxidative stress, which has been conclusively demonstrated to exist in smokers, vitamin E supplementation may not be sufficient to delay cataract formation.110 The Age Related Eye Disease Study (AREDS) was designed to test the efficacy of long-term dietary supplementation in preventing age-related macular degeneration (AMD). Results of the AREDS provided some evidence that antioxidants, vitamins and minerals, may be effective in preventing or treating AMD. This study focused on the effects of a combination of antioxidant vitamins A, C, and E and zinc on the development of cataracts and AMD. The results showed some protective effect of antioxidant supplements in preventing the progression of moderately advanced cases of dry macular degeneration or in preventing vision loss in individuals with unilateral wet macular degeneration.111 The overall findings of the AREDS study regarding antioxidant supplementation were published in the AREDS report No. 8.112 In contrast to the AREDS findings, another randomized trial of 1,193 subjects reported that after four years of supplementation, 500 IU per day of vitamin E had little benefit in reducing the risk of development or progression of AMD.113 The suggestion has been offered by AREDS investigators that, as in the AREDS study, too few of the subjects in this study progressed to advanced AMD. Indeed, at present this study may validate the AREDS finding that antioxidant vitamins, at the tested dose, appear to be of little benefit in the early stages of AMD. But there is the possibility they may be helpful in preventing the advanced stages that develop with inclusion of inflammatory processes.
Although it was noted that mortality in AREDS was half that observed in the general population, AREDS was not able to unequivocally prove the safety of high-dose antioxidant supplementation. This may be due to the fact that the typical volunteer for this study was healthy and mobile. The dose of vitamin C (500 mg) used in the formulation was approximately five times what the general population receives from diet alone. The 400-IU dose of vitamin E was approximately thirteen times the RDA while the dose of zinc, as zinc oxide, was approximately five times the RDA. These levels of zinc and vitamins C and E can usually be obtained only by supplementation.
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