Keeping an Eye on What You Eat: What's the Mediterranean Diet's Value in AMD?

The Mediterranean diet has been associated with a lower prevalence of age-related macular degeneration (AMD). However, a comprehensive prospective study involving a sufficiently large population to determine such a relationship had not been conducted to date. To address that gap, researchers from the EYE-RISK Consortium^[1] pooled data from two previously published prospective analyses: the Rotterdam Study I (RS-I)^[2] and the Antioxydants, Lipides Essentiels, Nutrition et Maladies Oculaires (Alienor) Study.^[3]

Eye examinations were performed every 5 years during a 21-year period (1990-2011) in RS-I, and during a 4-year period (2006-2012) in Alienor. Patients' compliance with the Mediterranean diet was evaluated using a 9-component score based on intake of vegetables, fruits, legumes, cereals, fish, meat, dairy products, and alcohol, and the monounsaturated-to-saturated fatty acids ratio. The components were then used to score and classify subjects as having low, medium, or high adherence to the Mediterranean diet.

The EYE-RISK analysis included 4996 participants (4446 from RS-I and 550 from Alienor) free of advanced AMD at baseline. Mean follow-up time was 9.9 years (range, 0.6-21.7 years) in RS-I and 4.1 years (range, 2.5-5.0 years) in Alienor. Of the patients included, 155 developed advanced AMD (117 from the RS-I and 38 from Alienor).

Analyzing the pooled results with an unadjusted model revealed that the incidence of advanced AMD was significantly lower in those with a high Mediterranean diet adherence score (hazard ratio [HR], 0.53; 95% confidence interval [CI], 0.33-0.84; P=.009 for trend). When adjusting for sex, total energy intake, AMD grade at baseline, education, body mass index, smoking, dietary supplement use, diabetes, hypercholesterolemia, and CFH Y402H/ARMS2 genes, the association was similar (HR, 0.59; 95% CI, 0.37-0.95; P=.04 for trend).

The Mediterranean diet was found to be more beneficial in the elderly population (85 years or older), but given that the prevalence of AMD increases with age, the association was considered similar in various age groups.

The authors concluded that following a diet of nutrient-rich foods including fruits, vegetables, legumes, and fish, and decreasing red/processed meat and salty food consumption, can possibly prevent advanced AMD.

Advantages and Limitations

EYE-RISK is rather comprehensive, given that it evaluated individual Mediterranean diet components and multidatabase pooled relationships in a large prospective population-based cohort. The resulting association between high adherence to the Mediterranean diet and reduced incidence of advanced AMD is similar to that reported by prior retrospective studies.

Although the comparable trend of results in the unadjusted and adjusted models suggests minimal confounding from such factors as sex and AMD grade at baseline, it is important to remember that EYE-RISK was not a randomized controlled study. Thus, it is difficult to make any conclusions on a causal or direct effect of the Mediterranean diet on the incidence of AMD.

In addition, recall bias and adherence are other factors to consider with the types of food frequency questionnaires used in RS-I and Alienor. Participants may not accurately recall the exact components and quantities of foods they consumed. Potential variability in the degree to which each participant consistently maintained their diet is another possible confounding detail.

Although this study is a step forward in determining the role of the Mediterranean diet in the progression of AMD to its advanced stages, it does not address prevention or disease reversal. Significant work on the role of diet in the multifactorial pathophysiology of AMD, as well as on the possible effect of dietary supplements, such as was done in the Age-Related Eye Disease Study (AREDS) trials, is still required.^[4,5]

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