Save Your Vision
Today’s Dietitian
By Leslie K. Kay, MS, RD
Vol. 6 No. 3 p. 52

March is National Save Your Vision Month, designed to increase awareness of eye health and help reduce incidence of serious and debilitating eye conditions such as cataracts, age-related macular degeneration (ARMD), glaucoma, and diabetic neuropathy. Populations with higher dietary intake of antioxidants, such as vitamins A, C, and E, plus several members of the carotenoid family, such as lutein and zeaxanthin, have a lower incidence of developing eye diseases, such as ARMD, cataracts, and glaucoma.1 This month’s “Supplement Spotlight” focuses on the dietary supplements with the best supportive research in protecting eye health.

Dietary supplements promoted for eye support may contain lutein, zeaxanthin, beta-carotene, vitamins E and C, the enzyme alpha-lipoic acid (ALA), and trace minerals that support the antioxidant enzyme pathway (glutathione) such as zinc, selenium, and copper. Herbal formulas are based on more traditional than clinical support, and these supplements often contain bilberry extract (Vaccinium myrtillus) and ginkgo extract.

There are hundreds of carotenoids, but lutein and zeaxanthin are the carotenoids found in highest concentration in the macular region of the eyes (the back of the eye where the retina is located), where they are believed to help filter out (or absorb) damaging blue light and prevent free radical damage to the delicate structures in the back of the eye. High dietary intake of lutein-rich fruits and vegetables has been associated with a significant reduction in macular degeneration, the leading cause of blindness in Americans over the age of 65.

Supportive claims for lutein and zeaxanthin include the following:
• prevents ARMD;
• may help prevent glaucoma and cataracts;
• supports normal eye health; and
• acts as an antioxidant.

Both lutein and zeaxanthin seem to reduce the risk of ARMD and protect overall eye health by concentrating in the eye to protect tissues by minimizing free radical damage and absorbing damaging blue light rays. It is thought that a low macular pigment density may increase the risk of ARMD and cataracts (by allowing more damage from blue light). Several observational studies have shown that high dietary intakes of lutein and zeaxanthin (from spinach, broccoli, and eggs) are associated with a significant reduction in the risk for cataracts (up to 20%) and ARMD (up to 40%).2 One study has shown that dietary supplementation with lutein (30 milligrams per day for 140 days) elevates serum lutein levels by 10 times, increases macular pigment density by 20% to 40%, and reduces transmission of blue light to the eye’s photoreceptors by 30% to 40%.

A multicenter clinical study (Eye Disease Case-Control Study) compared 356 patients with advanced ARMD (aged 55 to 80) to 520 control subjects, finding that the risk for ARMD was reduced by more than 40% by a high dietary intake of carotenoids. Both lutein and zeaxanthin were strongly associated with a reduced risk for macular degeneration.3

From studies of ARMD rates and dietary intake, it appears that diets providing approximately 6 milligrams of lutein and zeaxanthin per day can reduce ARMD and cataract formation. Unfortunately, recent diet surveys have indicated that consumption of these foods has dropped more than 20% in the two groups at highest risk for ARMD—women and older Americans. Some dietary supplements contain 20 milligrams of lutein as a recommended dosage. Larger doses increase levels of the antioxidants in the blood and are typically used in studies in subjects with advanced eye disease; however, it is not known whether or not higher amounts are more effective for treating these advanced eye diseases. Lutein and zeaxanthin appear to be safe when used at recommended levels. Some multiple vitamin/mineral supplements contain insignificant amounts of the carotenoids. Check supplement labels to verify that the product contains at least 6 milligrams of lutein and zeaxanthin.

Research suggests that nutrients with antioxidant properties may help to protect certain parts of the eye against oxidative stress and help maintain the normal function of blood vessels and nerves. It is thought that these eye diseases are accelerated by long-term damage from free radicals to proteins in the eye, primarily from sun and light exposure but also from smoking and other pollutants. Supplements with antioxidant properties may help defend the retina against the degradation of photochemical damage and may also maintain the normal function of blood vessels and nerves that supply the macular region. In numerous studies, antioxidants, such as vitamins A, C, and E, and supplementation with ALA are correlated with lowering the risk of developing eye disease and in slowing the damage or reducing symptoms.4

Antioxidant enzymes are also found in cell membranes. The Antioxidant Defense System is a group of antioxidant enzymes: superoxide dismutase, glutathione peroxidase, and catalase are found in cell membranes and fight free radicals. Trace minerals such as zinc, selenium, and copper are needed as coenzymes to complete antioxidant chemical reactions, so they are often included in dietary supplements promoted for eye health.

Nearly one-half of diabetic patients (approximately 5 million people in the United States) experience some type of neuropathy, a painful and sometimes debilitating disease of the eye caused by nerve damage from poor glycemic control. ALA, an enzyme found in the mitochondria, has been widely used in Germany since 1959 to treat diabetic neuropathy.5 In a double-blind, four-week study with 120 diabetic patients, an intravenous preparation of ALA (thioctic, not yet available in the United States) significantly reduced the frequency and severity of symptoms of diabetic neuropathy (eye pain and burning, prickling sensations, and numbness in patients with diabetic neuropathy). Researchers believe that the unique antioxidant properties of ALA (it functions as a fat- and water-soluble antioxidant) can reduce oxidative stress and improve the nerve function damaged by chronic hyperglycemia.

Although there have been relatively few studies conducted with ALA in humans, it appears to be safe as a dietary supplement. Intakes of as much as 600 milligrams per day have been used for treatment of diabetic neuropathy with no serious side effects, although typical doses range from 5 to 100 milligrams per day and appear to be safe.

Combinations of antioxidant nutrients may also play a synergistic, significant role in eye health. In a highly publicized study of 4,757 participants at 11 clinical centers conducted by the National Eye Institute, researchers from the Age-Related Eye Disease Study Research Group found that participants at high-risk for ARMD lowered their risk by approximately 25% when they took a combination of vitamins C and E, beta-carotene, zinc, and copper.6 In research findings involving the Beaver Dam Eye Study, significant, but modest, inverse associations were observed between intake of pro-vitamin A carotenoids and dietary vitamin E and the incidence of large lesions and between zinc and the incidence of pigmentary abnormalities associated with age-related maculopathy.7

Vitamins E and C and selenium all enhance glutathione levels. In a European-American cataract trial, 231 subjects who took a combination of vitamins C and E and beta-carotene for two years appeared to significantly reduce the progression of their age-related cataracts.

The synergistic effect of antioxidant vitamins and dietary intake make it difficult to pinpoint exactly how much of which nutrient is needed to treat or prevent eye disease. Recommending that your patients consume yellow vegetables and fruit and dark green, leafy vegetables—especially spinach, kale, and collard greens—would be prudent. Individuals with the highest spinach consumption reduce their risk of developing ARMD by almost 90%.

— Leslie K. Kay, MS, RD, has worked with the dietary supplement industry since 1985 and is a speaker on the topics of dietary supplements, alternative nutrition, and fad diets.

References
1. Taylor A. Nutritional and environmental influences on risk for cataract. In Taylor A, ed. Nutritional and Environmental Influences on the Eye. Boca Raton, Fla.: CRC Press; 1999: 53-93.
2. Berendschot, et al. Three methods to measure macular pigment density compared to lutein supplementation study. Invest Ophthalmol Vis Sci. 1999;40(4):S314.
3. Johnson EJ, et al. Relation among serum and tissue concentrations of lutein and zeaxanthin and macular pigment density. Am J Clin Nutr. 2000;71(6):1555-1562.
4. Seddon JM, et al. Dietary carotenoids, vitamins A, C, and E, and advanced age-related macular degeneration. JAMA. 1994;272(18):1413-1420.
5. Ametov AS, Barinov A, et al. The sensory symptoms of diabetic polyneuropahty are improved with alpha-lipoic acid. Diabetes Care. 2003;26(3):770-776.
6. Age-Related Eye Disease Study Research Group (AREDS). 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. Arch Ophthamol. 2001;119(10):1439-1452.
7. VandenLangenberg GM, et al. Associations between antioxidant and zinc intake and the 5-year incidence of early age-related maculopathy in the Beaver Dam Eye Study. Am vJ Epidemiol. 1998;148(2):204-214.

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