Opacification of the ocular lens, or cataract, occurs when lens proteins (crystallins) precipitate. This may result from an accumulation of modified (e.g., glycated) or oxidatively damaged lens proteins. The whole lens contains high amounts of vitamin E with a gradient found from the (outer) epithelium and cortex decreasing to lower amounts in the (inner) nucleus (22). A protective effect of vitamin E on cataractogene-sis was found in several animal studies in which vitamin E successfully delayed the progression of chemically induced cataracts (23-26).
Numerous epidemiologic studies have examined the associations between dietary vitamin E intake, supplement use, and blood vitamin E levels in relation to risk of different forms of cataract. As reviewed extensively by Taylor and Hobbs (27), most recent studies, whether retrospective or prospective, found an inverse association between vitamin E intake and risk of cataract, primarily on cortical rather than nuclear cataract. A recently published retrospective trial, the Nutrition and Vision Project, compared long-term nutrient intake and risk of early cataract among 478 participants of the Nurses' Health Study cohort (age 53-73 y). Intake and blood levels of vitamin E and C were inversely correlated with nuclear cataract; however, only the inverse correlation between blood vitamin E levels and risk of disease remained significant after adjustment for other nutrients (28).
A prospective study, the Longitudinal Study of Cataract (n = 764 participants), reported a 31% lower risk of newly diagnosed nuclear cataract by regular intake of multivitamins, and an ~50% risk reduction with regular use of vitamin E supplements or with higher blood vitamin E levels (29). In the prospective Beaver Dam Eye Study cohort (n = 1354 participants), no association between vitamin E intake and risk of cataract was observed, but blood vitamin E levels were inversely correlated with nuclear cataract (30), and a lower risk of cataract among long-term users of multivitamins or any dietary supplement containing vitamin C or E was observed (31).
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