August 20, 2012

6 Min Read
Ingredients for Eyesight

By Marie Spano, M.S., R.D., Contributing Editor

Everyone knows the connection between carrots and eyesight, but what other foods and compounds improve eye health?

Several compounds are important for eye functioning and prevention of eye disease. In particular, antioxidants have been examined because various structures within the eyes, particularly the lens, are susceptible to damage from reactive oxygen species (ROS; Journal of Biology and Chemistry, 1998; 273:28,60328,609). And, ascorbic acid, alpha tocopherol plus the carotenoids lutein and zeaxanthin are all found within the eye (Physiological Research, 2004; 53:1-10; Progress in Retinal and Eye Research, 2011; 30:188-203).

In addition to nutrients that protect the eyes, vitamin A is necessary for normal vision; a deficiency can lead to dry-eye syndrome, night blindness and blindness (Journal of Nutrition, 2008; 138:1,835-1,839). Zinc is necessary for normal retina functioning (Journal of the American College of Nutrition, 2001; 20:106-118). 

The most widely publicized eye study in recent years was the Age-Related Eye Disease Study (AREDS), which followed approximately 3,600 people with various stages of age-related macular degeneration (AMD). Each participant was randomly placed in one of four daily treatment groups: 1) 80 mg zinc oxide and 2 mg copper (copper was added to prevent zinc-induced anemia); 2) antioxidants (500 mg vitamin C, 400 IU vitamin E and 15 mg beta-carotene); 3) a combination of the same antioxidants, 80 mg zinc and 2 mg copper; or 4) a placebo. All three treatment groups reduced both risk of developing advanced AMD and risk of vision loss, although the antioxidant plus zinc group showed the greatest reductions in risk. Study subjects at high risk of developing advanced stages of AMD lowered their risk by about 25% by taking the multinutrient supplement while also reducing risk of vision loss due to advanced AMD by about 19%. No changes in risk of age-related cataracts were noted in the study (Archives of Ophthalmology, 2001; 119:1,439-1,452).

Though AREDS showed the multinutrient supplement had no effect on risk of developing age-related cataracts, several other studies indicate antioxidants have potential to do so. The Blue Mountain Eye Study found increasing vitamin C consumption was associated with a significantly reduced 10-year risk of incident nuclear cataract, and above-median intakes of vitamin E, beta-carotene and zinc from diet or dietary supplements were protective from the development of nuclear cataract (American Journal of Clinical Nutrition, 2008; 87:1,8991,905). Several other studies show lower prevalence of nuclear cataract in those with higher diet and/or supplemental intakes of vitamin C, higher serum vitamin C concentrations or general multivitamin use (Ophthalmology, 1998; 105:831836; American Journal of Epidemiology, 1995; 141:322334; American Journal of Ophthalmology, 2001; 132:1926; Ophthalmic Epidemiology, 2002; 9:4980).

Despite the positive effects of the antioxidant mix with zinc noted in AREDS, a Cochrane review of three randomized controlled trials (n=over 23,000) found neither beta-carotene nor alpha-tocopherol prevented or delayed AMD; this suggests a potential synergistic relationship between the antioxidants used in AREDS (Cochrane Database System Reviews, 2008; 23(1):CD000253).

Lutein and zeaxanthin make up macular pigment, help filter short-wavelength light and protect the retina from oxidative damage. Research suggests higher intakes of lutein and zeaxanthin improve visual performance by reducing glare disability, eye discomfort and inflammation. However, longitudinal studies are necessary prior to determining if this combination can reduce risk of AMD (Progress in Retinal and Eye Research, 2011; 30:188-203).

High levels of the omega-3 fatty acid docosahexaenoic acid (DHA) are found in the retina, and this fatty acid plays a role in the development of vision and retinal function (Agency for Healthcare Research and Quality, 2005). Dietary data collected during the 8-year period of AREDS found higher intakes of DHA (more than or equal to 64 mg per day versus less than 26 mg per day) and eicosapentaenoic acid (EPA) (more than or equal to 42.3 mg per day versus less than 12.7 mg per day) and lower dietary glycemic index were associated with a lower risk and progression of AMD, independent of AREDS supplementation (British Journal of Ophthalmology, 2009; 93:1,241-1,246). And, a review of nine studies found high dietary intakes of omega-3 fatty acids associated with a 38% reduction in risk of late AMD, and biweekly fish intake associated with a reduced risk of both early and late AMD (Archives of Ophthalmology,  2008; 126(6):826-833).

Vitamin D took center stage earlier this year after a small, yet widely publicized study conducted on mice. Mice injected with vitamin D for six weeks showed a decrease in retinal inflammation and proteins associated with normal aging, in addition to improved visual functioning compared to the control mice (http://dx.doi.org/10.1016/j.neurobiolaging.2011.12.002).

According to the National Eye Institute, Bethesda, MD, vitamin D may be produced in the cornea of the eye. Current research from this group is focusing on vitamin D metabolism in the cornea and cornea wound healing.

The majority of nutrients used in studies are consumed in a fraction of that amount in the typical diet. For instance, 80 mg of zinc was included in the AREDS, well above the tolerable upper limit and RDA set for zinc in adults: 34 to  40 mg per day and 9 to 13 mg per day, respectively. Typical dietary intakes, according to the most recent NHANES data, range from an average of 9.5 to 15.6 mg per day in adults (Office of Dietary Supplements, NIH; USDA, Agricultural Research Service, 2012). Likewise, a 400 IU dose of vitamin E used in AREDS is much higher than the RDA for adults (22.4 to 28.4 IU per day). And, the average American consumes less than half, and in some cases one-third, of the RDA for vitamin E. Average lutein and  zeaxanthin intake in Americans, ranging from 1.1 to 2.4 grams per day is also much lower than the amount used in research studies, as well as the quantities in dietary supplements (USDA ARS, 2012).

FDA labeling

Traditionally, claims for nearly any nutrient were based on deficiency disease," notes Billy Hammond, Ph.D., professor, behavioral and brain sciences program, University of Georgia, Athens, GA. "If a nutrient wasn't involved in some vital process (and its absence was not directly related to immediate disease) that nutrient was not essential." Therefore, structure/function claims can describe the role of a nutrient or dietary ingredient in the structure or function within the human body, as well as their role in general well-being or prevention of disease. Given this, manufacturers can add statements such as vitamin A supports eye health" to their product labels.

There isnt enough evidence at this time to suggest regular dietary supplementation for individuals with good eye health, but those with intermediate or advanced AMD may benefit from a mix of nutrients similar to the one used in the AREDS (Current Opinions in Ophthalmology, 2010; 21:184-189). In addition, several studies indicate dietary intake or supplementation of antioxidants may decrease risk of developing age-related cataracts. However, changes in eye health do not happen overnight, but instead over a lifetime. And, like all organs, the eyes are impacted by changes in other parts of the body. Therefore, to maintain good vision and decrease risk of eye disease it is important to keep the entire body healthy and consistently eat a diet rich in nutrients that support eye health.

Marie Spano, M.S., R.D., CSCS, is a nutrition communications expert whose work has appeared in popular press magazines, e-zines and nutrition-industry trade publications. She has been an expert guest on NBC, ABC and CBS affiliates on the East Coast. For more information, visit mariespano.com.

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