Background: It has been proposed that antioxidants may prevent cellular damage in the retina by reacting with free radicals produced in the process of light absorption.
Objectives: The objective of this review is to assess the effects of antioxidant vitamin and/or mineral supplementation on the progression of age-related macular degeneration.
Search strategy: The Cochrane Controlled Trials Register - CENTRAL/CCTR, which contains the Cochrane Eyes and Vision Group specialised register (Cochrane Library Issue 3 2001), MEDLINE (1966 to August 2001), EMBASE (1980 to September 2001), the Science Citation Index, and the reference lists of relevant articles were searched. Investigators of included studies were contacted for further information.
Selection criteria: Randomised trials comparing an antioxidant vitamin and/or mineral supplement (alone or in combination) to control in people with age-related macular degeneration are included in this review.
Data collection and analysis: The reviewer extracted data and assessed trial quality. Due to the variable methods of collecting and presenting outcome data, no statistical summary measure was calculated.
Main results: Seven trials, which randomised 4119 people with signs of age-related macular degeneration, are included in this review. One unpublished trial of zinc supplementation (170 participants) is awaiting assessment. The majority of people (88%) were randomised in one trial that found a modest beneficial effect of antioxidant and zinc supplementation on progression to advanced age-related macular degeneration (odds ratio 0.72, 99% confidence interval 0.52 to 0.98). People supplemented with antioxidants and zinc were less likely to lose 15 or more letters of visual acuity (equivalent to a doubling of the visual angle) (odds ratio 0.79, 99% confidence interval 0.60 to 1.04). This effect was seen more strongly in people with moderate to severe disease. There were few events in people with early signs of the disease. The trial evaluated many safety outcomes, of which hospitalisation for genitourinary problems was more common in people taking zinc and yellowing of skin was more common in people taking antioxidant micronutrients. The other six trials in this review were small and the results were inconsistent.
Reviewer's conclusions: The evidence as to the effectiveness of antioxidant vitamin and mineral supplementation in halting the progression of age-related macular degeneration is dominated by one large trial that showed modest benefit in people with moderate to severe signs of the disease. There is no evidence at present that people with early signs of the disease should take supplementation, however, current studies are underpowered to answer that question. Long term harm from supplementation cannot be ruled out, particularly in smokers. The generalisability of these findings to other populations with different nutritional statuses is not known. Further large well-conducted randomised controlled trials in other populations are required.