[Antioxidant micronutrients and cataract. Review and comparison of the AREDS and REACT cataract studies]

Age-related cataract remains the major cause of preventable blindness throughout the world. It has long been realized that one of the important etiological factors for this disease is oxidative and in particular photooxidative damage to the lens. Therefore, the antioxidant micronutrients, vitamins C and E and the carotenoids, in particular beta-carotene, have been discussed as factors that could reduce the risk for this disease. The present article reviews what is known about the transport of these substances to the lens, their accumulation, and their concentrations in the lens. Furthermore, the available epidemiological literature is briefly mentioned, but more emphasis has been placed on a description and discussion of major clinical intervention studies. Finally, the design and results of two of those trials using antioxidant micronutrients, the Age-Related Eye Disease Study (AREDS) and the Roche European American Cataract Trial (REACT), are compared. The AREDS trial did show a positive effect only for age-related macular degeneration but not for cataract, while the REACT trial demonstrated a small but statistically significant deceleration of cataract progression. The techniques for following the course of a cataract in the REACT study were more sensitive to subtle changes than those used in the AREDS study, and this may have been one important factor accounting for the differences. The authors' detailed comparison of these studies, however, suggests that even more important may have been the fact that in the REACT study intervention started earlier in the disease process,with higher doses of vitamins C and E and beta-carotene and consequently with larger plasma concentrations of these antioxidant micronutrients. The REACT trial results support the early complementation of a diversified diet with supplements containing vitamins C and E and beta-carotene as well as other carotenoids. The authors also believe that it is reasonable to include these micronutrients in the therapeutic armamentarium of general ophthalmological practice.