Submitted to: Investigative Ophthalmology and Visual Science
Publication Type: Review article
Publication Acceptance Date: 5/7/2013
Publication Date: 6/12/2013
Citation: Vishwanathan, R., Chung, M., Johnson, E.J. 2013. A systematic review on zinc for the prevention and treatment of age-related macular degeneration. Investigative Ophthalmology and Visual Science. 54(6):3985-3998. Interpretive Summary:
Technical Abstract: Zinc is a potential candidate for the prevention and treatment of age-related macular degeneration (AMD) due to its high concentration in the retina and role as a cofactor for antioxidant enzymes. The objective of this work was to conduct a systematic review of studies that investigated dietary intake of zinc from foods and/or supplements and risk of AMD. Medline® was searched from inception to 2nd week in February 2012. Data extraction and quality appraisal were done on all studies that met the pre-defined eligibility criteria. Meta-analysis was performed when studies reported sufficient data for the analyses. Ten studies were included: 4 were double-blinded, placebo-controlled randomized controlled trials (RCTs) and 6 were cohort studies. Of the 4 RCTs, the Age-related Eye Disease Study was the largest RCT and the results showed that zinc supplementation (80 mg/d) significantly reduced the risk of progression to advanced AMD. The other 3 RCTs reported changes in visual acuity scores as a primary endpoint. Pooled meta-analysis of these 3 RCTs showed that zinc supplementation (50 to 200 mg/d) improved visual acuity score (WMD = 3.00, 95%CI -0.04 to 6.04). Subgroup analysis found that the effects of zinc supplementation were more pronounced in subjects diagnosed with early AMD (WMD = 4.88, 95%CI 3.46 to 6.29), but were not significant in those with advanced AMD (reported in 1 RCT). Results from 6 cohort studies showed inconsistent associations between dietary zinc intake from foods and supplements and risks of early and late AMD. Treatment with zinc supplements can be effective in improving visual acuity in early AMD patients, but the role of zinc in the prevention of AMD is inconclusive due to inconsistent findings across cohort studies. Future research needs to focus on optimizing the type and dose of zinc supplements in patients with early AMD, and evaluating the effects of zinc supplementations with a longer follow up time and clinically meaningful AMD outcomes.