Age-related macular degeneration (AMD) is a degenerative disease of the macula and the leading cause of vision loss in people over the age of 55 in Westernized countries. It is a multifactorial disease to which genetic and non-genetic factors contribute. Fifty-two independent risk and protective single nucleotide polymorphisms associated with the disease have been identified, and non-genetic risk factors include age, smoking habits, poor diet, obesity and a sedentary lifestyle. Scientific evidence shows that the Mediterranean diet is protective against the disease and its progression.

AIBILI's AMD research group, led by Prof. Dr. Rufino Silva, has been studying how genetic and non-genetic factors can interact with each other to confer greater risk or protection for the disease. Thus, we evaluated whether the interaction between adherence to the Mediterranean diet and genetic risk for AMD can modulate the risk for the disease. The Coimbra Eye Study, promoted by AIBILI, is the only epidemiological study of AMD in Portugal and determined the prevalence, incidence and risk factors of AMD in 2 cohorts: Mira and Lousã. In this analysis, 161 cases and 451 controls were studied.

As the first author of this study on the interaction between environmental and genetic factors in AMD, it is worth noting the result of the great impact on knowledge of this disease: high adherence to the Mediterranean diet, when compared to low adherence, reduced the risk of the disease by 60%, adjusting for age, gender, physical exercise and smoking habits. In addition, the combined effect of having low adherence to the Mediterranean diet and high genetic risk for AMD significantly increased the risk for the disease by almost 5 times, compared to having high adherence to the Mediterranean diet and low genetic risk for AMD. People with a high genetic risk for AMD benefited most from adherence to the Mediterranean diet, with a statistically significant 60% reduction in the risk of disease, unlike the group of participants with a low genetic risk for AMD, in whom the Mediterranean diet reduced the risk of disease, but not significantly.

Statistical interaction models reflect whether the risk of the disease is different when two factors are considered in isolation or in association. The multiplicative model suggested that there was a positive interaction between the genetic risk for AMD and adherence to the Mediterranean diet, although it was not statistically significant: the risk for the disease was higher with the interaction between the two factors when compared to the product of the risk conferred by the factors alone. The additive model is more physiologically relevant, since risk factors in a biological context add to each other, not multiply. The statistically significant synergistic index, along with the other additive interaction metrics, also showed a positive interaction.

Genotyping patients with AMD is not recommended in clinical practice because it has no implication for patient follow-up. This research highlights the importance of continuing to analyze this data, since taking genetic risk into account could be beneficial in evaluating individual non-pharmacological strategies. In conclusion, a Mediterranean diet rich in vegetables, fruit, legumes and fish significantly reduces the risk of AMD, and this reduction is more relevant in people with a high genetic risk of the disease.