Experimental animal studies have suggested that dietary long-chain omega-3 polyunsaturated fatty acids, which are present in oily fish (such as salmon, mackerel, and sardines), may protect against diabetic retinopathy, a major cause of vision loss; however, clinical evidence is lacking. Spanish researchers undertook a prospective study of the association between intake of these dietary fats and incident diabetic retinopathy requiring laser photocoagulation, vitrectomy, and/or antiangiogenic therapy in adults ages 55 and older with type 2 diabetes enrolled in the randomized clinical Prevencion con Dieta Mediterranea study.

A total of 3,482 participants were assigned to one of three interventions: a Mediterranean diet supplemented with extra-virgin olive oil, a Mediterranean diet supplemented with nuts (walnuts, hazelnuts, and almonds), or a control diet with advice on how to reduce all dietary fat. Participants received instruction on how to follow the Mediterranean diet (of which fish is an important component), and adherence was monitored regularly. Questionnaires assessed dietary intake at baseline and annually.

The target amount of dietary intake of long-chain omega-3 polyunsaturated fatty acids was 500 mg/day-as recommended by the International Society for the Study of Fatty Acids and Lipids for primary cardiovascular prevention-which can be achieved by eating two servings of oily fish a week. A total of 75% of participants met the target recommendation for intake of these fatty acids at baseline.

During a mean six years of follow-up, 69 new diabetic retinopathy events were documented. The results showed that, after adjustment for intervention-group and lifestyle variables, participants who reported consuming at least 500 mg/day of long-chain omega-3 polyunsaturated fatty acids at baseline (regardless of which intervention group they were assigned to) had a 46% lower risk of incident "sight-threatening" diabetic retinopathy than those who did not consume the recommended amount.

Higher risk reductions were seen in participants with hypertension and in those who had diabetes for more than five years-confirming the benefits of dietary long-chain omega-3 polyunsaturated fatty acids in these critical groups. The association between meeting the recommended intake of long-chain omega-3 polyunsaturated fatty acids and decreased risk of severe retinopathy was slightly stronger when the yearly updated fatty acid intake was considered.

REFERENCE