By Vincent Sackey
School of Medical Sciences
University of Cape Coast
As stated by the New International Version of the Holy Bible, “The eye is the lamp of the body. If your eyes are healthy, your whole body will be full of light.” (Matthew 6:22)
Researchers have proved that nutrition has an essential role in the preservation and maintenance of vision. There is biological plausibility for a relationship between certain nutrients and certain eye diseases. This write-up considers eye diseases and conditions, and the beneficial nutrients to prevent or manage acquired cases. It is important to understand that nutrition can have a strong impact on eye diseases such as cataract, age-related macular degeneration (AMD), and retinitis pigmentosa (RP), which, together, account for approximately 60% of blindness worldwide. High dietary intake of vitamins C and E, starting early in life, may prevent the incidence of age-related nuclear cataracts, as well as AMD. Lutein and zeaxanthin intake may protect against nuclear and posterior subcapsular cataract (PSC), while vitamins B1, B2, B3, and folate may protect against nuclear and cortical cataract. Treatment with the Age-Related Eye Disease Study (AREDS) supplement (a combination of vitamins C and E, β-carotene, zinc, and copper) is beneficial for patients diagnosed with AMD.
Apart from the AREDS vitamins, it has been proven that high doses of lutein and zeaxanthin have also been shown to benefit AMD patients. Lutein has also been found to improve visual function because of its role as macular pigment in healthy and also AMD-affected eyes. Among the B vitamins, B 6, B 12 and folate have shown some protective indications as a result of their ability to reduce hyperhomocysteinemia, a risk factor for AMD. Apart from increasing consumption of foods rich in vitamin B6, B12 and micronutrients, eating a healthy, well-balanced diet is equally important in keeping the eyes healthy. Adhering to the Recommended Dietary Guidelines has been found to be associated with a reduced risk of nuclear cataract and advanced AMD. Greater intake of carbohydrates (≥200g/day) is also related to higher chances of cortical cataract. Looking at our Ghanaian staple, it is crucial to eat not just the right amounts, but also the right types of carbohydrates, because high-glycemic-index foods are associated with an increased prevalence of AMD, and of nuclear and cortical cataract. Replacing refined carbohydrates with whole grains such as brown rice, buckwheat, bulgur (cracked wheat), millet, oatmeal, popcorn and whole-wheat bread, and limiting consumption of added sugars would be beneficial. Similarly, the types of fat in the diet could also influence the course of eye diseases. Intake of the omega-3 fatty acids contained in soy, wheat germ, pumpkin, salmon, sardines, herring, mackerel docosahexaenoic acid present in salmon, trout, tuna, mussels, oysters, and arachidonic acid contained in chicken, and chicken mixed dishes, eggs and egg mixed dishes, beef and beef mixed dishes, sausage, franks, bacon, and ribs is essential for visual development right from birth. Omega-3 fatty acids have also been shown to benefit AMD and RP patients.
High intakes of omega-6 fatty acids contained in poultry, eggs, nuts, hulled sesame seeds, cereals, whole-grain breads, grape seed oil, soybean oil, safflower oil and corn oil can offset the omega-3 to omega-6 ratio, which has been shown to increase AMD risk. Adding one to two 85g servings of omega-3 rich fatty fish per week to the diet can be beneficial.
Omega-3 and omega-6 fatty acids, and also antioxidant-rich oils, ease dry-eye-related symptoms.
Retinitis pigmentosa (RP) patients may benefit from taking 15,000IU/day of vitamin A in conjunction with a low Vitamin E diet. Even though evidence for beneficial effects of anthocyanosides on visual function is minimal, adding anthocyanoside-rich foods like bilberries raspberries, blue and purple grapes, aubergines, and red cabbage to the diet may be helpful because of their antioxidant potential. From the evidences presented from researches, it may be more practical to recommend consumption of foods rich in vitamins C and E, B vitamins, lutein and zeaxanthin, omega-3 fatty acids, and zinc, rather than consuming the nutrient in isolation, thus, benefiting from the synergistic effects of all the components in the food.
Cataract is a medical condition characterised by the clouding of the lens of the eye which prevents clear vision. Although most cases of cataract are related to the ageing process, occasionally, children can be born with the condition, or a cataract may develop after eye injuries, inflammation, and some other eye diseases.
Highly contained in guavas, mustard spinach, citrus, papaya, and strawberries, the interest in studying Vitamin C for cataract prevention and treatment results from the fact that its accumulation in the lens is 30 to 35-fold greater than in plasma. Not only is Vitamin C a strong antioxidant, but it also has the ability to absorb ultra violet light, which has been linked to significant eye problems, including cataracts, macular degeneration, pingueculae, pterygia and photokeratitis.
Vitamin E highly contained in sunflower oil, almond oil, avocado, mango and peanuts, acts as a strong chain-breaking antioxidant in lipid peroxidation processes in vivo (Bunce et al., 1990). Vitamin E may, thus, protect the lens from oxidative damage. Epidemiological studies that have evaluated the role of dietary Vitamin E from food and supplements in the development and progression of cataracts have yielded mixed results. Studies reported a reduced incidence of nuclear cataract with high Vitamin E intake, for a long duration supplementation.
The human lens contains significant amounts of lutein and zeaxanthin, but not β-carotene and lycopene, which are the dominant carotenoids in serum. Of the total lens lutein and zeaxanthin, 75% is present in the epithelium and cortex. All epidemiological studies that looked at relations between carotenoid intake and cataract extraction found a significant reduction in the incidence of cataract extraction with higher intake of dietary lutein and zeaxanthin contained in spinach, mustard seeds, green peas and not β-cryptoxanthin, lycopene, or α- and β-carotene.
Flavin dinucleotide (FAD), a cofactor for the enzyme glutathione reductase (GR), is derived from the B vitamin riboflavin. GR is necessary for maintaining the cellular pool of reduced glutathione, which is an important antioxidant that prevents the formation of protein disulfides and maintains transparency of the lens. Additionally, riboflavin deficiency has also been shown to interfere with the metabolism of folate, vitamins B12 and B 6 (Powers, 2003). There is ample epidemiological data showing reduced prevalence of nuclear opacities with the high dietary intake of either one or a combination of two or more B vitamins, which include riboflavin, folate, thiamin or niacin.
Zinc is a component of antioxidant enzymes such as superoxide dismutase, which is involved in the maintenance of the structural integrity of the lens proteins (Flood et al., 2002; Trumbo et al., 2001). Zn2+ can also specifically interact with α-crystallin, a major lens protein, and molecularchaperone, and enhance its ability to prevent protein aggregation and maintain lens transparency (Biswas et al., 2007).
However, compared with other antioxidants such as vitamins C and E and carotenoids, epidemiological data on zinc intake and cataract prevalence are minimal.
The Blue Mountains eye follow-up study has shown that above-median intakes of zinc in combination with vitamins C and E and β-carotene were associated with reduced incidence of nuclear cataract, but not cortical or PSC cataract.
Magnitude of the Problem
According to the latest assessment, cataract is responsible for 51% of world blindness, which represents about 20 million people (WHO, 2010). VISION 2020: THE CATARACT CHALLENGE has estimated around 800 million cases in 2020 due to population growth (Foster, 2000). This then calls for urgent and collaborative efforts to curb the incidence of cataract and other eye-related conditions. Foreign aids, governmental, ministerial, and non-governmental agencies or stakeholders must plan towards implementing steps, and ensuring the use of food containing diverse nutritional supplementations to prevent this menace. Looking at all the benefits of these nutrients, readers must take their eye health into their own hand