November 2018 Issue
Integrative Nutrition: Food for the Eyes
By Densie Webb, PhD, RD
Today's Dietitian
Vol. 20, No. 11, P. 14
What part does diet play in preventing AMD?
There are many reasons for vision loss—cataracts, corneal dystrophy, diabetic retinopathy, dry eye, glaucoma—but age-related macular degeneration (AMD) is the leading cause of vision loss in the United States. According to the American Macular Degeneration Foundation, AMD affects more than 10 million Americans; that's more than cataracts and glaucoma combined. If the disease progresses after diagnosis, people experience wavy or blurred vision, and, if the condition continues to worsen, central vision may be lost.
What It Is
AMD is caused by the deterioration of the sensitive central portion of the retina, called the macula, the inside back layer of the eye that records images and transmits them via the optic nerve from the eye to the brain. It's also responsible for focusing central vision in the eye. AMD rarely affects side vision. There are two main types of macular degeneration: "dry" and "wet." About 85% to 90% of AMD cases are the dry (atrophic) type, while 10% to 15% are the wet (exudative) type. While wet AMD accounts for only a small percentage of total cases, it accounts for 90% of severe vision loss in people with AMD.1 There's also a form of AMD found in young people called Stargardt disease, which is caused by a recessive gene.
Diagnosis
Most people, as they age, develop drusen—small yellow deposits that don't affect vision—beneath the retina. However, larger drusen are a sign that AMD is present. The following are the three stages of AMD:
• Early AMD: Diagnosed by the presence of medium-sized drusen, which are about the width of a human hair. Typically, there's no vision loss at this stage.
• Intermediate AMD: Large drusen are present, as well as pigment changes in the retina. It may cause some vision loss, but there will be no indication without an examination by an ophthalmologist.
• Late AMD: In addition to drusen, vision loss is present.
Treatment
AMD is irreversible. However, the treatment for early dry AMD is nutritional therapy consisting of a diet high in antioxidants, especially flavonoids and the carotenoids lutein and zeaxanthin, along with a supplement specifically designed to support the cells of the macula and prevent further damage. Wet AMD can be treated with anti-VEGF (anti–vascular endothelial growth factor) therapy injections in the eye, which sometimes can prevent further vision loss by inhibiting the formation of new blood vessels behind the retina.
Diet for Prevention
A growing body of research strongly suggests that diet is an important factor in the prevention of AMD and its progression. Flavonoids and carotenoids, two diverse groups of naturally occurring phytochemicals found in many plant foods, appear to be especially beneficial. Foods rich in flavonoids include citrus fruits, berries, apples, tea, red wine, and legumes, while eggs and red and orange fruits and vegetables are especially rich in carotenoids. Findings from two recent studies highlight these dietary connections.
Dietary intake was assessed in 2,856 adults, aged 49 and older, and then followed up 15 years later for analysis. The researchers found that diets rich in flavonols and total flavanones (two types of flavonoids) were associated with a reduced risk of AMD. Those with the highest intake of flavanones had a 57% reduced likelihood of developing AMD. Citrus fruit appeared to be especially protective. Participants in the study who reported consuming at least one serving of oranges per day had a lower risk of AMD compared with those who never consumed oranges at the beginning of the study.2
A second paper analyzed 18 high-quality studies and found that adherence to a Mediterranean diet, rich in vegetables and fatty fish, was associated with a decreased risk of AMD progression, whereas a Western dietary pattern, high in red and processed meat, refined grains, eggs, and fried potatoes, was associated with increased incidence of AMD. High consumption of vegetables rich in carotenoids and fatty fish containing omega-3 fatty acids was beneficial for those at risk of AMD, whereas high-glycemic diets and consuming more than two alcoholic drinks per day was associated with increased risk.3 Green leafy vegetables, such as spinach and kale, have been singled out as excellent sources of the flavonoids associated with a reduced risk of AMD.4
While the previous study included eggs in the definition of a Western diet as an unhealthful component, other findings contradict that assumption. It has been reported that daily intake of three eggs for 12 weeks increased lutein and zeaxanthin intake by 21% and 48%, respectively, in 20 adults.5 Lutein and zeaxanthin are well absorbed from egg yolks. The authors concluded that egg yolk could be an important dietary source to improve lutein and zeaxanthin status for the prevention of AMD in adults.
Another study of 40 healthy adults, aged 50 and older, found that consuming one avocado per day (avocados are a bioavailable source of lutein) for six months increased serum lutein levels by 25% and was associated with increased macular pigment density, which suggests a reduced risk of developing AMD.6
A recent review paper highlighted experimental and observational studies that suggest low vitamin D status to be a potential risk factor for AMD.7 Dietary and supplemental zinc also have been shown to decrease the risk of developing and slow the progression of AMD.8,9 Dietary vitamin E has been associated with reduced risk, but some studies have shown no benefit.9,10
AMD Supplement
Two studies, the Age-Related Eye Disease Study (AREDS) and AREDS2 were major clinical trials sponsored by the National Eye Institute of the National Institutes of Health to test the efficacy of specific dietary supplement formulas on the risk of developing AMD. Results from the study showed that high levels of antioxidants and zinc significantly reduce the risk of advanced AMD and its associated vision loss.11 There are no government-recommended daily intakes for lutein or zeaxanthin, but, according to the American Optometric Association, the average adult consumes only about 1 to 3 mg per day of lutein and zeaxanthin combined from foods, well below amounts suggested to be beneficial for eye health. As a result of the AREDS studies, the following nutrients currently are recommended by the American Macular Degeneration Foundation to reduce the risk of developing AMD (supplements that provide this combination of nutrients are available):
• lutein 6 to 10 mg;
• zeaxanthin 2 mg;
• vitamin C 500 mg;
• vitamin E 200 to 400 IU;
• vitamin D3 1,000 to 2,000 IU;
• zinc 20 to 80 mg (though the research on zinc's effects on AMD has been inconsistent); and
• omega-3 fatty acids 1,000 mg (if not eating fish).
Choosing the eye-healthy foods is recommended regardless of age or stage of AMD. Dietary recommendations for prevention of AMD include the following:
• Consume kale, spinach, broccoli, peas, avocados, tomatoes, and other fruits and vegetables with high levels of antioxidants, including lutein and zeaxanthin.
• Eat foods containing high levels of zinc. These include high-protein foods, such as lean beef, pork, and lamb. Nonmeat sources include milk, cheese, yogurt, whole grain cereals, and whole wheat bread.
• Consume foods high in omega-3 fatty acids, such as salmon, tuna, and walnuts.
Summary
While family history of AMD is unavoidable, diet and nutrient intake clearly have been associated with risk. Other modifiable risk factors, such as smoking and inactivity, also play roles. Quitting smoking and engaging in regular physical activity can reduce risk along with diet. Clients and patients should be educated to understand that saving sight is an additional health benefit of consuming a diet low in highly processed foods and high in fruits, vegetables, and whole grains.
— Densie Webb, PhD, RD, is a freelance writer, editor, and industry consultant based in Austin, Texas.
References
1. Morris B, Imrie F, Armbrecht AM, Dhillon B. Age-related macular degeneration and recent developments: new hope for old eyes? Postgrad Med J. 2007;83(979):301-307.
2. Gopinath B, Liew G, Kifley A, et al. Dietary flavonoids and the prevalence and 15-y incidence of age-related macular degeneration. Am J Clin Nutr. 2018;108(2):381-387.
3. Chapman NA, Jacobs RJ, Braakhuis AJ. Role of diet and food intake in age-related macular degeneration: a systematic review [published online June 21, 2018]. Clin Exp Ophthalmol. doi: 10.1111/ceo.13343.
4. Eisenhauer B, Natoli S, Liew G, Flood VM. Lutein and zeaxanthin — food sources, bioavailability and dietary variety in age-related macular degeneration protection. Nutrients. 2017;9(2):E120.
5. Abdel-Aal el–SM, Akhtar H, Zaheer K, Ali R. Dietary sources of lutein and zeaxanthin carotenoids and their role in eye health. Nutrients. 2013;5(4):1169-1185.
6. Scott TM, Rasmussen HM, Chen O, Johnson EJ. Avocado consumption increases macular pigment density in older adults: a randomized, controlled trial. Nutrients. 2017;9(9):E919.
7. Layana AG, Minnella AM, Garhöfer G, et al. Vitamin D and age-related macular degeneration. Nutrients. 2017;9(10):E1120.
8. Smailhodzic D, van Asten F, Blom AM, et al. Zinc supplementation inhibits complement activation in age-related macular degeneration. PLoS One. 2014;9(11):e112682.
9. van Leeuwen R, Boekhoorn S, Vingerling JR, et al. Dietary intake of antioxidants and risk of age-related macular degeneration. JAMA. 2005;294(24):3101-3107.
10. Schleicher M, Weikel K, Garber C, Taylor A. Diminishing risk for age-related macular degeneration with nutrition: a current view. Nutrients. 2013;5(7):2405-2456.
11. National Institutes of Health, National Eye Institute. Age-Related Eye Disease Study — results. https://nei.nih.gov/amd. Updated May 2013. Accessed September 10, 2018.