Dietary antioxidants and primary prevention of age related macular degeneration: systematic review and meta-analysis

Age related macular degeneration (AMD) is the leading cause of severe visual loss in people aged over 50 in the developed world. Early AMD is characterised clinically by yellow deposits known as drusen and changes in pigmentation of the retina. Late AMD develops when there is an ingrowth of new blood vessels that bleed into the subretinal space (exudative or "wet" type) or when the macula atrophies (geographic atrophy or "dry" type). Both these conditions usually lead to severe loss of central vision. The pathogenesis of AMD is unclear older age, genetic markers, and cigarette smoking are the only risk factors consistently reported. Although new treatments have emerged, they are suitable only for the small proportion of people with "wet" AMD. No treatments are available for the "dry" form, and there is little to offer for the primary prevention of AMD in older people.

Dietary antioxidants have long been suggested as useful for preventing the development and progression of AMD. The retina, with its high oxygen content and constant exposure to light, is particularly susceptible to oxidative damage. A large randomised clinical trial, the age related eye disease study (AREDS), showed that patients with intermediate AMD treated with high dose antioxidant supplements (vitamins C and E, zinc, and  carotene) had a 28% reduction in the risk of progression to advanced AMD compared with placebo (odds ratio 0.72, 99% confidence interval 0.52 to 0.98). That study did not specifically examine whether antioxidant supplements were effective for the primary prevention of early AMD in people without signs of this condition.

Because oxidative damage could cause drusen to form, antioxidants may be beneficial in the earliest stage of AMD. Randomised control trials and observational studies have been conducted in well nourished Western populations, but evidence of the role of dietary antioxidants as a primary preventive measure for AMD remains unclear. Some studies, but not others, indicate that diets rich in antioxidants may protect against the development of signs of early AMD, and the common perception is that a diet rich in antioxidants can protect against AMD.

We performed a systematic review and meta-analysis of the role of a range of dietary antioxidants—vitamins A, C, and E; zinc; lutein and zeaxanthin;  carotene;  carotene;  cryptoxanthin; and lycopene—in the primary prevention of AMD. We considered only randomised clinical trials and prospective cohort studies for inclusion.