Volume 80, Issue 10 , Pages 590-591, October 2009
What eye care patients should know about nutrition
Article Outline
Research has identified 6 nutrients that promote healthy vision and may reduce the risk of eye diseases. Sufficient quantities of these nutrients are generally not obtained through a normal diet. Nutritional supplements are an easy way to obtain the recommended levels.
Treatment options for chronic age-related eye diseases are limited, invasive, and expensive. The only U.S. Food and Drug Administration–approved treatments options for AMD are Lucentis® (Genentech, South San Francisco, California), Macugen® (Pfizer Inc., New York, New York), and Visudyne® (Novartis Pharma AG, Basel, Switzerland) all of which are vitreal injections aimed to stop abnormal blood vessel growth. There is no surgical treatment available for those with AMD, and it is estimated that the federal government spends more than $3.4 billion each year treating cataracts through the Medicare program.3 Therefore, proper nutrition is an attractive way to improve and maintain eye health.
A healthy diet includes 5 to 9 servings of fruits and vegetables every day, at least 3 servings of 100% whole grains each day, and 2 servings of fish each week.4 Strong evidence has shown the importance of certain nutrients found in a healthy diet in reducing the risk for age-related eye diseases such as AMD and cataract. Specifically, the National Eye Institute–sponsored Age-Related Eye Disease Study (AREDS) published in 2001 provided evidence that vitamins C and E, beta-carotene, zinc, and copper taken in supplement form reduced AMD progression by 25%, and the risk of moderate vision loss by 19% in a subset of subjects.5 Additional research suggests that the carotenoids lutein and zeaxanthin, as well as the omega-3 fatty acids, docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA) may help reduce the risk of age-related eye disease.6
Nutrients important for eye health and function
The AREDS guidelines recommend intake of 6 essential nutrients.
Lutein and Zeaxanthin act as antioxidants, which help to protect and maintain healthy cells. They also act like an internal pair of sunglasses for the eyes as they filter harmful, high-energy blue wavelengths of light that can damage cells. Studies have found that lutein and zeaxanthin supplementation can increase an individual's tolerance for glaring light and enable them to recover more quickly after exposure to glare. Increased levels of lutein and zeaxanthin in the macula have also been shown to help improve visual range, visual performance, and contrast acuity in study subjects (see related article). The human body is unable to synthesize lutein and zeaxanthin. Dark green vegetables such as kale, spinach, and broccoli are especially good sources of lutein and zeaxanthin and typically provide on average 1 to 2.5 mg daily to the U.S. population.7 Research findings suggest 10 mg per day of lutein and up to 2 mg per day of zeaxanthin from dark green leafy vegetables and other sources is necessary to realize the health benefits of these molecules. Because only 23% of Americans eat the recommended amount of fruit and vegetables per day, taking supplements containing lutein may be an effective way to increase intake.4
Vitamin C (ascorbic acid) helps promote healthy capillaries, cartilage, and the absorption of iron. Virtually all cells in the body depend on it, including those in the eye (in which it is heavily concentrated in all tissues). Vitamin C also supports the health of ocular blood vessels. Human bodies do not synthesize the amounts of vitamin C needed, which is the reason citrus fruits and juices containing vitamin C are essential to good nutrition. Numerous studies including AREDS have linked vitamin C intake and ocular health. A study found that women using vitamin C for 10 years or more experienced a 64% reduction in the risk for nuclear cataracts.8 Researchers estimate that half of cataract-related surgeries could be averted by delaying the onset of cataracts for 10 years.9 Other research found that women taking a daily vitamin C supplement experienced a 57% reduction in their risk of certain types of cataracts.10 The recommended dietary allowance (RDA) for vitamin C is 90 mg per day for men and 75 mg per day for women. Scientific research, including AREDS, suggests a daily intake of 500 mg per day to benefit from its positive impact upon eye health.5
Vitamin E plays a significant role in the immune system, the health of cell membranes, deoxyribonucleic acid (DNA) repair, and other metabolic processes. The human body does not synthesize vitamin E, which is the reason nuts, fortified cereals, or sweet potatoes are essential to good nutrition. A recent study found that higher dietary intakes of lutein, zeaxanthin, and vitamin E were associated with significantly decreased risk of cataracts.11 The RDA for vitamin E is 22.5 international units (IU) per day from natural sources for both men and women. Research suggests 400 IU per day of vitamin E can help maintain healthy vision.5
Zinc is an essential trace mineral that plays a vital role in delivering vitamin A from the liver to the retina.12 Zinc is highly concentrated in the eye, mostly in the retina and choroid. A deficiency of zinc can result in conditions such as impaired vision and cloudy cataracts. The human body does not synthesize the zinc it needs, which is the reason why meat, seafood, eggs, wheat germ, mixed nuts, black-eyed peas, tofu, or baked beans are essential to good nutrition. Along with other nutrients, zinc was shown in the AREDS trial to reduce the progression of AMD.5 The RDA for zinc is 11 mg for men and 8 mg for women per day. For individuals at high risk for AMD or experiencing early-stage AMD, a daily intake of 40 to 80 mg zinc may help slow the progression of the disease. However, high doses of zinc, such as those given in the AREDS trial, may cause stomach upset. In the follow-up trial, AREDS 2, the effect of a formulation containing a lower dose (25 mg/d) of zinc on the progression and development of AMD will be assessed. Also, zinc supplementation has been known to interfere with copper absorption, so 2 mg per day of copper is strongly recommended for people supplementing their diet with zinc.
Omega-3 fatty acids are critical to many biological functions of the human body. Omega-3 fatty acids, particularly DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid), support the cardiovascular, reproductive, immune, and nervous systems.13 They also are needed for proper neural development, including visual development and maturation of sensory systems.14 DHA is found in the highest concentration in the retina, suggesting it has an important functional role. EPA is used in DHA biosynthesis. Low levels of DHA and EPA have been associated with eye diseases such as AMD, diabetic retinopathy, and retinopathy of prematurity as well as dry eye syndrome.13, 15 Although the body does produce omega-3 fatty acids, studies have found that increased consumption of DHA and EPA through higher intake of fleshy fish such as salmon or tuna as well as supplementation with these fatty acids can improve eye health. Studies suggest a daily intake of essential fatty acids at 500 mg per day can have positive effects on eye health.
Summary
Intensive research has identified 6 essential nutrients that promote healthy vision and may reduce the risk of eye diseases. Small changes in diet can have a positive impact on eye health and quality of life. Because the human body does not synthesize all of these nutrients, it is essential to be proactive by taking steps to improve the variety and quality of the foods we eat. The daily intake of these nutrients required for good eye health is typically greater than that obtained from a normal diet or, in certain instances, from the general daily value. Therefore, nutritional supplements are an easy way to obtain the recommended levels for eye health.
References
- Prevalence of age-related macular degeneration in the United States. Arch Ophthalmol. 2004;122(4):564–572
- Vision Problems in the U.S. Report developed by the National Eye Institute and Prevent Blindness America. Chicago: Prevent Blindness America; 2002.
- . The genetics of cataract. Invest Ophthalmol Vis Sci. 2001;42(8):1677–1678
- United States Department of Health and Human Services and United States Department of Agriculture. Dietary Guidelines for Americans 2005. January 12, 2005. Available at: www.healthierus.dietaryguidelines. Accessed June 16, 2009.
- A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta carotene, and zinc for age- related macular degeneration and vision loss: AREDS report no. 8. Arch Ophthalmol. 2001;119(10):1417–1436
- The Relationship of Dietary Carotenoid and Vitamin A, E, and C Intake With Age-Related Macular Degeneration in a Case-Control Study: AREDS Report No. 22. Arch Ophthalmol. 2007;125(9):1225–1232
- Centers for Disease Control and Prevention. National Center for Health Statistics. National Health and Nutrition Examination Survey Data 2001-2002. Available at: www.cdc.gov/nchs/about/major/nhanes/nhanes01-02.htm. Accessed June 16, 2009.
- Vitamin C is associated with reduced risk of cataract in a Mediterranean population. J Nutr. 2002;132(6):1299–1306
- . Bowman lecture. The conquest of cataract: a global challenge. Trans Ophthalmol Soc U K. 1985;104(Pt 1):1–10
- Long-term intake of vitamins and carotenoids and odds of early age-related cortical and posterior subcapsular lens opacities. Am J Clin Nutr. 2002;75(3):540–549
- Dietary carotenoids, vitamins C and E, and risk of cataract in women: a prospective study. Arch Ophthalmol. 2008;126(1):102–109
- Zinc: a trace element essential in vitamin A metabolism. Science. 1973;181(103):954–955
- . The role of omega-3 long-chain polyunsaturated fatty acids in health and disease of the retina. Prog Retin Eye Res. 2005;24(1):87–138
- . Essential fatty acids: the importance of n-3 fatty acids in the retina and brain. Nutr Rev. 1992;50(4 (Pt 2):21–29
- Prospective study of dietary fat and the risk of age-related macular degeneration. Am J Clin Nutr. 2001;73(2):209–218
PII: S1529-1839(09)00425-4
doi:10.1016/j.optm.2009.08.006
Volume 80, Issue 10 , Pages 590-591, October 2009
