Searching for the Antioxidant, Anti-Inflammatory, and Neuroprotective Potential of Natural Food and Nutritional Supplements for Ocular Health in the Mediterranean Population

Abstract

Adherence to a healthy diet offers a valuable intervention to compete against the increasing cases of ocular diseases worldwide, such as dry eye disorders, myopia progression, cataracts, glaucoma, diabetic retinopathy, or age macular degeneration. Certain amounts of micronutrients must be daily provided for proper functioning of the visual system, such as vitamins, carotenoids, trace metals and omega-3 fatty acids. Among natural foods, the following have to be considered for boosting eye/vision health: fish, meat, eggs, nuts, legumes, citrus fruits, nuts, leafy green vegetables, orange-colored fruits/vegetables, olives-olive oil, and dairy products. Nutritional supplements have received much attention as potential tools for managing chronic-degenerative ocular diseases. A systematic search of PubMed, Web of Science, hand-searched publications and historical archives were performed by the professionals involved in this study, to include peer-reviewed articles in which natural food, nutrient content, and its potential relationship with ocular health. Five ophthalmologists and two researchers collected the characteristics, quality and suitability of the above studies. Finally, 177 publications from 1983 to 2021 were enclosed, mainly related to natural food, Mediterranean diet (MedDiet) and nutraceutic supplementation. For the first time, original studies with broccoli and tigernut (chufa de Valencia) regarding the ocular surface dysfunction, macular degeneration, diabetic retinopathy and glaucoma were enclosed. These can add value to the diet, counteract nutritional defects, and help in the early stages, as well as in the course of ophthalmic pathologies. The main purpose of this review, enclosed in the Special Issue "Health Benefits and Nutritional Quality of Fruits, Nuts and Vegetables," is to identify directions for further research on the role of diet and nutrition in the eyes and vision, and the potential antioxidant, anti-inflammatory and neuroprotective effects of natural food (broccoli, saffron, tigernuts and walnuts), the Mediterranean Diet, and nutraceutic supplements that may supply a promising and highly affordable scenario for patients at risk of vision loss. This review work was designed and carried out by a multidisciplinary group involved in ophthalmology and ophthalmic research and especially in nutritional ophthalmology.

Keywords: Mediterranean diet; antioxidant/anti-inflammatory/neuroprotective properties; broccoli; eye diseases; natural food; nutritional supplements; saffron; tigernuts-chufa de Valencia; walnuts.

Figure 1

Comparative evaluation of the MPOD measured with the Visucam 500^®. (A) Retinography of the central retina of the right eye at baseline, (B) Distribution of the macular pigment and the peak at the foveal level of the right eye at baseline. (C) Retinography of the central retina of the right eye of the same participant at end-of-study. (D) Distribution of the macular pigment and the peak at the foveal levels of the righ eye of the same participant at end-of-study (E) Schematic representation of the retinal area where the pigment is placed (a). (F) Illustrative drawing of the Visucam 500 parameters: total pigment volume (b), maximum of the pigment density (c), mean of the pigment density (d) [81].

Figure 2

Immunohistochemistry of retinal whole-mount micrographs of mice eyes. The A,B retinas were labeled with anti-Iba-1 (microglia), showing the comparison of Iba-1 + microglia in the OHT untreated (A) and treated with saffron extract (B) eyes in the outer plexiform layer of the retina. It has been noted that in the OHT mice eyes treated with saffron extracts, less activation and fewer microglial cells were observed than in the untreated eyes. The C,D retinas were stained with anti Brn3a (RGCs). The C,D comparative micrographs showed the Brn3a + RGCs in the untreated (C) and treated with saffron extract (D) mice retinas. It was also detected a higher RGCs density in the treated versus the untreated rat retinas. RGC: retinal ganglion cells.

Figure 3

Clinical probes to qualitative and quantitative evaluating the tear film from baseline to the end of study in the participants randomly assigned to a daily intake of 30 g. of the fresh TN Chufa de Valencia. (A) Data from the FTBUT in both eyes. (B) Schirmer test determination in both eyes. F-BUT test: Fluorescein break up time test; RE: right eye LE: left eye. ^★ p < 0.05 statistically significant.

Figure 4

Parameters of the Macular Pigment Ocular Density. The volume is expressed in relative densitometry units (rdu). RE: right eye. LE: left eye. ^★ p value < 0.05.

Figure 5

Parameters of Oxidative Stress in Chufa de Valencia intake, determined by TAC and MDA/TBARS. TAC: Total antioxidant capacity; MDA/TBARS: Malondialdehyde/thiobarbituric acid reactive substances; ^★ p < 0.05.