A Randomized, Placebo-Controlled, Clinical Trial of High-Dose Supplementation With Vitamins C and E and Beta Carotene for Age-Related Cataract and Vision Loss

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Abstract
THE FACT that oxidative damage of lens proteins is a prominent feature of cataract development1,2 has led to speculation that micronutrients with antioxidant capabilities, such as vitamin C (ascorbic acid), vitamin E, and the carotenoids, may retard cataract development.3 However, retrospective, cross-sectional, and prospective epidemiological studies of cataract and intake or blood levels of antioxidant nutrients have not produced consistent results.4-27 Most studies with published findings have noted protective associations for various nutrients, but there is no consensus about the specific nutrient(s) that may be involved or the specific type of cataract(s) that might be affected. A major concern in interpreting the results of observational epidemiological studies of micronutrient intake and cataract risk is the possibility of unadjusted confounding. A high degree of correlation between intake levels of various nutrients makes it difficult to identify which of many candidate nutrients might "explain" any observed associations. Confounding could also result if persons with better nutritional status are different from others in unrecognized ways that affect the risk of cataract.