Eating at least two weekly servings of oily fish, rich in omega-3 polyunsaturated fatty acids (PUFAs), can help middle-aged and older people with type 2 diabetes reduce their risk for diabetic retinopathy, suggests a post hoc analysis of a major diet trial.

After adjusting for factors including age, sex, and intervention group, researchers from the PREDIMED trial found that participants who were 55 years or older and consumed at least 500 mg/day of omega-3 PUFAs showed a 48% reduced risk for incident diabetic retinopathy compared with those who consumed less than 500 mg/day (hazard ratio, 0.52; P = .001).

“Higher risk reductions were observed in participants with hypertension, those with diabetes of greater than 5 years’ duration, and those treated with insulin at baseline,” according to the report from Aleix Sala-Vila, DPharm, PhD, a researcher at CIBER-Fisiopatología de la Obesidad y Nutrición, Institut d’investigacions Biomèdiques August Pi i Sunyer, in Barcelona, Spain, and colleagues, published online August 18 in JAMA Ophthalmology.

Results align with findings from experimental models and with what researchers already know about how omega-3 cells affect diabetic retinopathy, according to the group.

“It is a fact that the amount of omega-3 in our body, and therefore in our retina, can be modulated by our diet,” Dr Sala-Vila told Medscape Medical News. “A sustained consumption of two weekly servings of fatty fish will increase the levels of omega-3 in cells. This would prevent or at least counteract inflammation in our body, a key player in the onset and progression of diabetic retinopathy. Our data reinforce a notion to date only explored in animals.”

Dr Sala-Vila said it is unclear whether supplements might have the same effect as eating fish and pointed to possible doubts raise by the ORIGIN trial (N Engl J Med. 2012;367:309-318). The trial showed no reduction of cardiovascular events over 6 years for participants initially at high cardiovascular risk who took 1000 mg/day of omega-3 PUFAs in a supplement.

Authors of the current study summarize its contribution to the literature: “Our findings support the view that regular consumption of oily fish might be beneficial to delay the onset or progression of vascular diseases in arterial beds other than the coronary and cerebrovascular ones.”

Study Based on PREDIMED Data

Data were analyzed from people with type 2 diabetes in PREDIMED, a nutrition intervention trial conducted in Spain that tested Mediterranean diets supplemented with extra virgin olive oil or nuts vs a low-fat control diet for primary cardiovascular prevention.
The current analysis is based on a PREDIMED subcohort of 3614 persons with type 2 diabetes at baseline; their aged ranged from 55 to 80 years. Full data were available for 3482 participants (48% men; average age, 67 years). Food intake was assessed at baseline and yearly for 6 years of follow-up using a 137-item food-frequency validated for the PREDIMED study. Then researchers interviewed participants on frequency of consumption of each food item in the past year and asked about usual portion sizes.

The main outcome was incident diabetic retinopathy requiring laser photocoagulation, vitrectomy, and/or antiangiogenic therapy. After a follow-up of an average 6 months, researchers found 69 new diabetic-retinopathy events.

Even More Benefit in United States?

In an accompanying editorial, Michael Larsen, MD, DMSc, department of ophthalmology, Rigshospitalet-Glostrup and University of Copenhagen in Glostrup, Denmark, notes that the study was conducted in Spain, primarily in large urban centers, where fish is a mealtime staple.

“Fish and nuts are already part of the food culture, available in every supermarket, cafeteria, and restaurant and in most households.” It is no surprise, he says, that 75% (2611 participants) met target omega-3 consumption levels at baseline.

He told Medscape Medical News that the potential for change in preventing diabetic retinopathy is greater in the United States, where consumption of fish and tree nuts (also high in omega-3 PUFAs) is much lower.

“If the results can be verified and if they extrapolate to the bottom stratum of the [omega-3] scale, where many of us roam, the implications for public health will be considerable,” he writes. “The potential value of a large-scale switch to a diet rich in [omega-3] fatty acids merits serious attention.”