Although a high intake of beta-carotene containing foods has been associated with the prevention of cataracts, the role of supplementation is uncertain. An assessment of dietary beta-carotene intake in a subgroup of 472 non-diabetic women, aged 53-73 years, who participated in the Nurses' Health Study found that the odds of posterior subcapsular cataracts was 72% lower in those with the highest intakes of beta-carotene who had never smoked, whereas beta-carotene intake and cataract risk were not associated in current or past smokers (Taylor et al 2002). This finding is contrasted with findings from intervention studies that have found that beta-carotene may help prevent cataracts in smokers (Christen et al 2003, 2004). Two years of beta-carotene treatment was found to have no large beneficial or harmful effect on the development of cataract in a randomised, double-masked, placebo-controlled trial of 39,876 female health professionals aged 45 years or older who participated in the Women's Health Study, although a subgroup analysis suggests a possible beneficial effect in smokers (Christen et al 2004). Similarly, a randomised, double-masked, placebo-controlled trial of 22,071 male physicians aged 40-84 years found that supplementation with 50 mg of beta-carotene on alternate days for 12 years did not reduce the overall incidence of cataracts or cataract extraction; however, in a subgroup of smokers the risk of cataract was reduced by approximately 25% (Christen et al 2003).

In two randomised, double-masked trials involving 5390 nutritionally deprived subjects in Linxian, China, supplementation with selenium, alpha-tocopherol and beta-carotene for 5-6 years was found to significantly reduce the prevalence of nuclear but not cortical cataracts in older subjects (Sperduto et al 1993). This is contrasted with the finding that 500 mg of vitamin C, 400 IU of vitamin E and 15 mg of beta-carotene had no apparent effect on the 7-year risk of development or progression of age-related lens opacities or visual acuity loss in a relatively well-nourished older adult cohort of 4629 people aged from 55 to 80 years who participated in the Age-Related Eye Disease Study (AREDS) (Kassoff et al 2001).

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