In the news: Modified Med Diet Reduces Retinopathy Risk: Carotenoids Linked to Lower AMD

Modified Med Diet Reduces Retinopathy Risk

To date, no clinical trials have specifically evaluated the role of dietary patterns in the incidence of microvascular diabetes complications, according to the investigators of the PREvención con DIeta MEDiterránea or PREDIMED Study. These researchers hypothesized that a nutritional intervention based on the Mediterranean diet (MedDiet) would have a protective effect on diabetic retinopathy and nephropathy. The PREDIMED Study was a multicenter, randomized nutritional intervention trial conducted in a population at high risk for CVD.

This post hoc analysis (1) looked at a cohort of over 3,600 PREDIMED participants with type 2 diabetes who were free of microvascular complications at enrollment. Participants were randomly assigned to one of three dietary interventions: MedDiet supplemented with extra virgin olive oil, MedDiet with mixed nuts, or a low-fat control diet.

During a median follow-up of 6 years, 74 new cases of retinopathy and 168 of nephropathy were identified. The results showed that a MedDiet enhanced with extra virgin olive oil significantly decreased incident diabetic retinopathy by 44% compared to the low-fat control diet (adjusted Hazard Ratio = 0.56, 95% CI, 0.32–0.97).

A relative risk reduction, though non-significant, was also seen for the MedDiet plus nuts vs. the control diet. Unlike the results from some observational studies that found favorable effects of the MedDiet on kidney function, no effects on nephropathy were seen in this analysis.

Carotenoids and Advanced AMD Risk

While the primary analyses of the AREDS2 trial failed to prove a protective effect of lutein/zeaxanthin, a 26% reduction in risk was seen for participants at the bottom 20% of dietary intake of these carotenoids. Given the unlikely occurrence of another large-scale, randomized trial like AREDS2, data from large and long-running prospective cohort studies may be the best evidence we’ll have to evaluate the potentially protective role of lutein/zeaxanthin.

Harvard researchers recently examined associations between carotenoid intakes and AMD in two large, prospective cohorts with repeated dietary assessments who were followed for over two decades (24-26 years) (2). Data was analyzed from more than 63,000 females in the Nurses’ Health Study and 38,600 males in the Health Professionals Follow-Up Study.

The researchers computed predicted plasma carotenoid scores directly from food intake, assessed by repeated food frequency questionnaires.
Associations between predicted plasma carotenoid scores and AMD were determined.

About 2.5% of the participants developed either intermediate or advanced AMD (mostly wet AMD) during the follow-up. Comparing highest vs. lowest quintiles of predicted plasma lutein/zeaxanthin scores showed a risk reduction for advanced AMD of about 40% in both women and men (pooled relative risk comparing extreme quintiles = 0.59; 95%CI, 0.48-0.73; P for trend < .001).

Predicted plasma carotenoid scores for other carotenoids, including β-cryptoxanthin, α- and β-carotene, were associated with a 25% to 35% lower risk of advanced AMD when comparing top and bottom quintiles. No link between carotenoids and intermediate AMD was seen.

The authors point out that α-carotene and β-carotene are found in human RPE and choroid where they could protect against light-induced oxidative damage and locally produced free radicals. While very high dose supplemental β-carotene competitively reduced absorption of lutein/zeaxanthin in AREDS2, consuming a wide variety of fruits and vegetables – i.e. a carotenoid-rich diet – may be a sound public health strategy for reducing the risk of advanced AMD.

References

1. Diaz-Lopez A, et al. Mediterranean Diet, Retinopathy, Nephropathy, and Microvascular Diabetes Complications: A Post Hoc Analysis of a Randomized Trial. Diabetes Care; Published online before print Sept. 13, 2015.
2. Wu J, et al. Intakes of Lutein, Zeaxanthin, and Other Carotenoids and Age-Related Macular Degeneration during 2 Decades of Prospective Follow-up. JAMA Ophthalmol. Published online October 8, 2015.