Dietary vitamin and carotenoid intake and risk of age-related cataract

Background: Existing studies suggest that dietary vitamins and carotenoids might be associated with a reduced risk of age-related cataract (ARC), although a quantitative summary of these associations is lacking. Objectives: The aim of this study was to conduct a meta-analysis of randomized controlled trials (RCTs) and cohort studies of dietary vitamin and carotenoid intake and ARC risk. Methods: The MEDLINE, EMBASE, ISI Web of Science, and Cochrane Library databases were searched from inception to June 2018. The adjusted RRs and corresponding 95% CIs for the associations of interest in each study were extracted to calculate pooled estimates. Dose-response relations were assessed with the use of generalized least-squares trend estimation. Results: We included 8 RCTs and 12 cohort studies in the meta-analysis. Most vitamins and carotenoids were significantly associated with reduced risk of ARC in the cohort studies, including vitamin A (RR: 0.81; 95% CI: 0.71, 0.92; P = 0.001), vitamin C (RR: 0.80; 95% CI: 0.72, 0.88; P < 0.001), vitamin E (RR: 0.90; 95% CI: 0.80, 1.00; P = 0.049), beta-carotene (RR: 0.90; 95% CI: 0.83, 0.99; P = 0.023), and lutein or zeaxanthin (RR: 0.81; 95% CI: 0.75, 0.89; P < 0.001). In RCTs, vitamin E (RR: 0.97; 95% CI: 0.91, 1.03; P = 0.262) or beta-carotene (RR: 0.99; 95% CI: 0.92, 1.07; P = 0.820) intervention did not reduce the risk of ARC significantly compared with the placebo group. Further dose-response analysis indicated that in cohort studies the risk of ARC significantly decreased by 26% for every 10-mg/d increase in lutein or zeaxanthin intake (RR: 0.74; 95% CI: 0.67, 0.80; P < 0.001), by 18% for each 500mg/d increase in vitamin C intake (RR: 0.82; 95% CI: 0.74, 0.91; P < 0.001), by 8% for each 5-mg/d increase in beta-carotene intake (RR: 0.92; 95% CI: 0.88, 0.96; P < 0.001), and by 6% for every 5 mg/d increase in vitamin A intake (RR: 0.94; 95% CI: 0.90, 0.98; P < 0.001). Conclusions: Higher consumption of certain vitamins and carotenoids was associated with a significant decreased risk of ARC in cohort studies, but evidence from RCTs is less clear.