Even if you are reading this without glasses, it's not too early to start taking your eye vitamins. Some nutrients can stave off the burdensome vision loss and eye disease that occur as we age, mounting research suggests.



But claims by supplement manufacturers about the powers of eye-friendly antioxidants are frequently overblown. And though carrots have long been touted as a magical sight-booster, other foods, including dark, green leafy vegetables, may have a stronger impact on your peepers.



More than 150 million Americans use glasses or contacts to correct refractive errors such as nearsightedness or farsightedness, according to a report from the eye health organization Prevent Blindness America. And the prevalence of blindness and sight problems increases with age. In people over age 40, the most common diseases include age-related macular degeneration (AMD), cataracts, diabetic retinopathy and glaucoma.



Studies over the last few decades suggest that people whose diets are high in specific antioxidants such as vitamin C, E, zinc, or carotenoid plant pigments such as beta-carotene or lutein are less likely to develop common age-related eye diseases, said Julie Mares, a professor of ophthalmology and visual sciences at the University of Wisconsin at Madison.



But Mares cautions that it's better to get these nutrients through whole foods, rather than supplements, which usually provide only single nutrients and may be lacking other critical compounds. Researchers are finding that those who eat a wide range of healthy foods "have much lower odds for having age-related diseases," said Mares an expert in nutrition and vision.



A new study published in the journal Ophthalmology showing that vitamins E and C did nothing to help protect aging eyes from macular degeneration — the longest-running study to test vitamin E for eyesight in men, and the first to try out vitamin C alone — further confirms the lack of benefits of single antioxidants, said Mares.



Nutritious diets may yield a higher density of macular pigment, according to a study co-written by Mares. This important yellow pigment contains the lutein and its sister compound zeaxanthin, which are thought to protect the back of the eye. Other protective nutrients and plant chemicals contained in fruits, vegetables and whole grains may help by reducing the breakdown of lutein and zeaxanthin, Mares said.



Still, sales of vision supplements in the U.S. reached $370 million in 2010, a 6 percent increase over the previous year, according to estimates by Nutrition Business Journal. Lutein, multivitamins and fish oil are the most popular eye-related products, NBJ said.



Read on to see which nutrients show the most promise of improving eye health and where researchers are still in the dark.



Antioxidant vitamins + zinc



What's clear: The antioxidant vitamins C, E, beta carotene and zinc reduced the risk of developing advanced AMD by about 25 percent, according to the National Eye Institute's original Age-Related Eye Disease Study (AREDS). The dosage included 500 milligrams of vitamin C, 400 International Units (IUs) of vitamin E, 15 mg of beta-carotene, combined with 80 mg of zinc and 2 mg of copper (to prevent anemia from the high dose of zinc).



Still foggy: This specific cocktail hasn't been shown to prevent or delay the onset AMD; only to slow the progression in people who already have either a moderate or advanced case. Current data also don't support the use of antioxidants — or herbal medications — to prevent or treat cataracts, glaucoma or diabetic retinopathy, according to a literature review by researchers at Oregon Health Science University, published in the 2011 issue of the journal Drugs.



Lutein and zeaxanthin



What's clear: Lutein and zeaxanthin could help younger people improve vision, new data suggest. This may be because the carotenoids can absorb blue light, which is especially damaging to the back of the eye or retina, said Mares. "They can also act as antioxidants and quench free radicals that occur due to light exposure," she said. Increasing the level of macular pigment — which can usually be boosted by eating foods high in lutein — may help people see contrast, studies suggest. This might be important in low light or glare conditions. It may also decrease the risk of developing macular degeneration.



Still foggy: So far, there's no association between lutein/zeaxanthin and vision in non-glare conditions. Moreover, early data suggest that some people are low responders and may not be able to increase the lutein levels in their eyes as easily as others can, even with supplements, said Mares. Studies suggest that "people who have diabetes, obesity, low-fat or low-fiber diets and certain genetic characteristics have lower levels of lutein and zeaxanthin in the retina, regardless of their dietary intake of lutein and zeaxanthin," said Mares.



Omega-3 fatty acids



What's clear: Essential fatty acids could help treat dry-eye syndrome, a condition that occurs when the eye can't produce enough tears for lubrication, according to a 2011 study from the Mount Sinai School of Medicine. The American Optometric Association recommends eating fish or taking a nutritional supplement that contains a polyunsaturated fatty acid to help with dry eye. The essential omega-3 fatty acid decosahexanoic acid (DHA), found in breast milk, is crucial for vision and brain development in infants. Breast milk is also enhanced with lutein relative to other types of carotenoids, especially in the first months of life.



Still foggy: It is known that formula-fed infants do not see as well as infants who are fed breast milk. But adding DHA to infant formula hasn't been shown to improve vision, so other nutrients may be at play. Formula companies have started adding lutein, but so far, there's little evidence that such enriched formula can improve vision.



Vitamin D



What's clear: Made by the body when the skin is exposed to sunlight, vitamin D also helps lower inflammation and slows the development of abnormal blood vessels that contribute to AMD. Studies have shown women who had high vitamin D levels had lower odds of early AMD.



Still foggy: Beyond a certain level, higher levels of D didn't have greater impact. Mares' research also suggests that vitamin D may enhance the benefit of other aspects of diet. The protective effect may be stronger when people have higher amounts of lutein, she said.



jdeardorff@tribune.com