Plain language summary

Antioxidant vitamins and mineral supplements to slow down the progression of age-related macular degeneration

Age-related macular degeneration (AMD) is a condition affecting the central area of the retina (back of the eye). The retina can deteriorate with age and some people get lesions that can lead to loss of central vision. It has been suggested that progression of the disease may be slowed down in people who eat a diet rich in antioxidant vitamins (carotenoids, vitamins C and E) or minerals (selenium and zinc). The author identified nine randomised controlled trials; four trials based in the USA, four in Australia, Austria, Switzerland and the UK and one in China. The review of trials found that supplementation with antioxidants and zinc may be of modest benefit in people with AMD. Long-term harm from these supplements cannot be ruled out. Large well-conducted trials in a range of populations and with different nutritional status are required.

Here is the scientific abstract:

Abstract

Background

It has been proposed that antioxidants may prevent cellular damage in the retina by reacting with free radicals that are produced in the process of light absorption.

Objectives

The objective of this review was to assess the effects of antioxidant vitamin or mineral supplementation on the progression of age-related macular degeneration (AMD).

Search strategy

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library (2007, Issue 3); MEDLINE (1966 to August 2007); EMBASE (1980 to August 2007); NRR (2007, Issue 3); AMED (1985 to January 2006); PubMed (24 January 2006 covering last 60 days) and SIGLE (1980 to March 2005), reference lists of identified reports and the Science Citation Index. We contacted investigators and experts in the field for details of unpublished studies.

Selection criteria

We included randomised trials comparing antioxidant vitamin or mineral supplementation (alone or in combination) to a control intervention in people with AMD.

Data collection and analysis

The author extracted data and assessed trial quality. Where appropriate, data were pooled using a random-effects model unless three or fewer trials were available in which case a fixed-effects model was used.

Main results

Nine trials were included in this review. The majority of people were randomised in one trial (AREDS in the USA) that found a beneficial effect of antioxidant (beta-carotene, vitamin C and vitamin E) and zinc supplementation on progression to advanced AMD (adjusted odds ratio 0.68, 99% confidence interval 0.49 to 0.93). People taking supplements were less likely to lose 15 or more letters of visual acuity (adjusted odds ratio 0.77, 99% confidence interval 0.58 to 1.03). Hospitalisation for genito-urinary problems was more common in people taking zinc and yellowing of skin was more common in people taking antioxidants. The other trials were, in general, small and the results were inconsistent.

Authors’ conclusions

The evidence as to the effectiveness of antioxidant vitamin and mineral supplementation in halting the progression of AMD comes mainly from one large trial in the USA. The generalisability of these findings to other populations with different nutritional status is not known. Further large, well-conducted randomised controlled trials in other populations are required. Long-term harm from supplementation cannot be ruled out. Beta-carotene has been found to increase the risk of lung cancer in smokers; vitamin E has been associated with an increased risk of heart failure in people with vascular disease or diabetes.