Age-related macular degeneration can lead to distortion or complete loss of sight. About a third of people over 75 years of age have early signs, and one in twelve have late stage disease. No effective treatment has been found that will restore vision and, in the absence of cure, prevention clearly is the best option. The authors of a recently updated Cochrane review investigated the evidence for one type of prevention: antioxidant vitamins and minerals.

Observational studies have found conflicting results for the relationship between these vitamins and minerals in a person’s diet and their risk of developing age-related macular degeneration. The Cochrane reviewers set out to discover if the use of these vitamins and minerals as supplements had any effect on the incidence of age-related macular degeneration. They looked for randomised trials of vitamins C and E, carotenoids, zinc and selenium in which the supplementation was to last at least one year. A separate review provides knowledge on the use of these supplements to slow the progression of age-related macular degeneration in people who already have the disease.

The authors of the Cochrane review did not limit their searching to studies targeting age-related macular degeneration. They searched for all trials comparing these supplements with control in healthy populations, hoping that some of these might have collected data on age-related macular degeneration. When they worked on this review initially, they also searched for randomised trials in which the supplements had been tested for people with diseases other than age-related macular degeneration. They no longer do this, abandoning it as inefficient having failed to find any trials suitable for this review.

The authors searched a mixture of databases and identified more than 3000 records, within which were about 200 potentially relevant articles. After working through these, the authors had seven randomised trials of the supplements in healthy people. However, three of these trials did not measure age-related macular degeneration, a fourth has not responded to the Cochrane reviewers and a fifth is ongoing. This left two trials that could be included, both of which had studied carotenoids. There was one other trial that had tested Vitamin E specifically for age-related macular degeneration.

In total, more than 23,000 people had been randomised into the three trials. Just under 800 of them developed age-related macular degeneration. But, despite such large numbers, there was no significant difference between the incidence in the supplementation or the control group. The authors conclude that there is no evidence that healthy people should take antioxidant vitamin and mineral supplements to prevent age-related macular degeneration. They eagerly anticipate the outcome of ongoing research in which thousands more people have been randomised; the findings of which will be included in future updates of this review.

This Cochrane review is available in full at www.mrw.interscience.wiley.com/cochrane/clsysrev/articles/CD000253/frame.html

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March 24 2008