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Out of Sight
Vision loss is an inevitable part of aging. What you eat could help forestall it.
By Helene Ragovin
The signs of vision loss come on slowly and painlessly in most cases. First, it’s hard to read a menu in a dimly lit restaurant. Then words on the page start to blur; colors seem less intense. Eventually, even well-loved faces become shadowy and unfamiliar. It can be frightening and isolating—and it happens more often than most people realize.
Almost all of us will deal with some form of eye disease as we age. Cataracts await the vast majority, and while those can usually be remedied through surgery, other sight-threatening conditions are still difficult, or impossible, to control. One in three people over the age of 75, for example, develops age-related macular degeneration (AMD), which has no cure and can lead to blindness.
“Some estimate that by 2020, macular degeneration will be epidemic, because people are living so much longer and developing the disease,” says Johanna Seddon.
For the 76 million baby boomers, in particular, it’s an eye-opening revelation—the generation that has relied on contact lenses and Lasik to stave off wearing glasses will find itself facing far more serious eye issues. Not to mention the potential strain on the health-care system, and the associated costs.
“Some estimate that by 2020, that magic ‘perfect-vision’ year, macular degeneration will be epidemic, because people are living so much longer and developing the disease,” says Johanna Seddon, a professor at Tufts School of Medicine and director of the ophthalmic epidemiology and genetics service at the New England Eye Center at Tufts Medical Center.
One way to tame the threat may be through what we eat. Scientists at the Jean Mayer USDA Human Nutrition Research Center on Aging (HNRCA) at Tufts and elsewhere have been conducting work on the connection between diet and eye diseases.
Specifically, they’ve been looking at AMD and cataracts, the two eye conditions that affect the largest number of people in the United States. While researchers stress that diet alone is not a cure, there is promise that some relatively simple dietary changes could help forestall some of the worst aspects of these diseases.
“If we could delay the onset of AMD and cataracts for 10 years, we could eliminate 50 percent of the medical problems” associated with them, says Allen Taylor, head of the Laboratory for Nutrition and Vision at the HNRCA and a professor at the Friedman School of Nutrition Science and Policy. Taylor’s recent work has looked at the connection between the consumption of diets high in simple sugars and the development of AMD and cataracts.
Even for the elderly and those already afflicted with eye disease, “our data is telling us that people can still gain some advantage by modifying their diet even fairly late in life,” Taylor says. “But I certainly would be advising my children, and my children’s children, to begin a prudent diet.”
Nutritious Vision
Blindness and low vision (partial vision loss that cannot be corrected) affect 3.3 million Americans age 40 and over, or 1 in 28, and are projected to affect 5.5 million by the year 2020, according to the National Eye Institute. AMD is the major cause of blindness among white Americans, while glaucoma and cataracts are the leading causes among African Americans and Hispanics, with genetics and health-care disparities accounting for the differences. (No data is available on prevalence of eye disease for Asian Americans or American Indians.)
These diseases strike different parts of the eye. Cataracts are a clouding of the lens. In most cases, the damaged lens can be surgically removed and replaced with an artificial lens. AMD affects the macula, the area at the back of the eye that’s responsible for central vision. Glaucoma, an umbrella term for a family of diseases that destroy cells in the optic nerve, erodes peripheral vision. Neither AMD nor glaucoma is curable; vision lost to either cannot be restored completely.
Of these conditions, researchers have been most successful in establishing nutritional ties to AMD. A major National Eye Institute project, the Age-Related Eye Disease Study, completed in 2001, found that high levels of antioxidants—vitamins C and E and beta-carotene—along with zinc and copper, significantly reduced the risk of advanced AMD and its associated vision loss in at-risk individuals.
Other research has shown that two micronutrients in the carotenoid family, lutein and zeaxanthin, may be particularly useful in protecting the macula. “When we think about lutein and zeaxanthin, and AMD, it’s one of the most compelling nutrition-disease relationships there is,” says Elizabeth Johnson, an assistant professor at the Friedman School and a scientist at the HNRCA.
Lutein and zeaxanthin are the yellow pigments found in leafy green vegetables—in greens that have wilted and lost their emerald sheen, the yellow left behind is the lutein and zeaxanthin. Another good source is egg yolk; while eggs don’t contain as much lutein and zeaxanthin as green vegetables, what is there is extremely “bioavailable,” or easy for the body to extract and use.
Zeaxanthin is also found in corn. (Mexican Americans, whose traditional diet is often based on corn tortillas and other cornmeal products, tend to have high levels of zeaxanthin, for example.) The Asian berry known as goji, fructus lycii or wolfberry contains extraordinarily high levels of zeaxanthin and has been used for centuries to promote eye health. Carrots, the food usually touted as being “good for your eyes,” contain almost no lutein and zeaxanthin, although they are rich in beta-carotene, which the body converts to vitamin A, a crucial nutrient for vision.
A second National Eye Institute study is underway; in addition to the antioxidants examined in the first study, lutein, zeaxanthin and an omega-3 fatty acid have been added to the mix.
Together, lutein and zeaxanthin make up the macula pigment. Scientists believe the macula pigment acts as a sort of shock absorber—or, in this case, a light absorber—protecting the eye against oxidation and light damage. The denser the macula pigment, the more protection available.
“It’s one of the most compelling nutrition-disease relationships there is,” Elizabeth Johnson says of age-related macular degeneration and the micronutrients lutein and zeaxanthin. Photo: Alonso Nichols
Popeye Was Right
Seddon recommends her patients eat a diet rich in lutein and zeaxanthin. In 1994, while at the Massachusetts Eye and Ear Infirmary, she published the first systematic evaluation of the dietary content of lutein and zeaxanthin in food and how it related to AMD. “Those results indicated a profound effect, and subsequent studies have shown the same thing,” she says.
Lutein outpaces zeaxanthin in the American food supply by about 5 to 1, so it is the more often discussed member of the pair, Johnson said. The recommended daily intake for both is 6 mg, but most Americans don’t get nearly that much. The most plentiful common source of lutein is spinach—a scant half-cup raw serving is enough to meet the daily recommendation.
“And with lutein, it’s not a case of ‘more is better,’ ” Johnson says. “If you’re taking mega-supplements, you’re just wasting your money.”
In most cases, the experts say, it’s better to eat lutein-rich foods, which contain other nutrients and fiber, rather than resort to supplements. The most noteworthy exceptions are heart patients, who need blood-thinning medications such as warfarin and are advised to avoid spinach and greens because of possible food-drug interactions, or those prone to kidney disease, because the oxalates in greens may contribute to formation of kidney stones. Johnson advises those looking for an “eye-health” vitamin to check for a lutein content of close to 6 mg per dose; some products contain only minute quantities.
Because of the tough cellular walls of spinach and other greens, they should be cooked a little to get the most nutritional benefit. And, Johnson says, greens should be consumed along with a small amount of a healthful fat to allow absorption of the lutein.
Omega-3 fatty acids may be particularly beneficial. A study by Johnson published in the May issue of the American Journal of Clinical Nutrition suggests that DHA, an omega-3 fatty acid, enhances the amount of lutein that can be absorbed by the retina.
In fact, dietary fats may have their own effects on eye health. Earlier work by Seddon found that diets high in omega-3 fatty acids were linked to macular health. She also warns that saturated fats and trans fats can increase risk for AMD. “It’s not just about total fat; it’s about the kind of fat you eat,” Seddon says.
A good source for the helpful omega-3s is fatty fish. “Eat a couple of servings of fish per week,” Seddon advises. “The omega-3s might be helpful for AMD and other diseases as well.” Salmon, herring, sardines, mackerel, lake trout and albacore tuna are all high in omega-3s.
The Sugar Trap
In most young people, the center of the eye’s lens is crystal clear. Over a lifetime, however, the lens slowly tints, turning yellow, then amber, then brown. And often, cloudy, opaque spots—cataracts—develop.
For Allen Taylor, this process evoked the image of a sliced apple, turning brown as it sits on a table. Based on his training in biochemistry, he believed the same principle was responsible for both phenomena.
“It all has to do with oxidation—specifically, the oxidation of carbohydrates,” Taylor says. In work that has opened a new direction for vision research, Taylor and his colleagues examined the relationship between intake of foods that are high on the glycemic index (GI)—meaning foods that are rapidly converted to glucose in the body—and the development of AMD and cataracts.
“Simple-sugar intake sets up the body for damage when sugar is oxidized,” Taylor says. And those simple sugars are present in the American diet like never before. “Our diet is now 50 percent higher in simple sugars than it was 30 years ago,” says Taylor. The effects are being seen in many ways, such as in rising obesity rates. Another probable result, Taylor says, is the prevalence of cataracts.
“If you live long enough, you’ll get a cataract,” he says. While a damaged lens can be replaced, “for people who are frail and elderly, the last thing they need is another procedure, or to have their abilities compromised. And there is a huge cost: cataract surgery is the biggest line-item in the Medicare budget,” he adds.
Taylor’s lab looked at high-glycemic index diets in relation to AMD and cataracts, using data from long-term studies. The results showed that those who consumed diets high in simple sugars, as compared to complex carbohydrates, had a higher risk of developing cataracts and AMD. They also developed them at a younger age.
“And more than that,” Taylor says, “in people with lower-GI diets, the disease progressed slower. So you’re protected in two ways—delayed progress and delayed risk.” According to the study, if patients with early stage AMD switched to a low-GI diet, 7.8 percent of advanced cases could be avoided over the next five years.
Taylor is not talking about drastic dietary changes. For people who eat white bread, for example, “by only changing five slices of bread from white to whole-wheat, that would change the GI enough to get into a healthier range,” he says. “That shows just how subtle, how doable, how achievable this type of dietary management is.”
Eye on the Heart
Doctors and researchers stress there are many other factors besides diet that affect the development and progression of AMD.
“Smoking is a very strong risk factor, stronger than any other, except for genetics,” Seddon says. “And that includes exposure to second-hand smoke.”
Age and gender (women are affected in greater numbers than men) are also risk factors, as are body mass index and waist-to-hip ratio (the “apples” are at higher risk than the “pears.”) High blood pressure and cholesterol levels may play a part as well.
Does the list sound familiar? It should—those are many of the same risk factors for cardiovascular disease.
“If you look up close, on a microvascular level, what you see in the eye is what you see in the heart,” Johnson says. “The nice thing about preventive measures for AMD is that they are consistent with everything we know about preventing heart disease and cancer: high consumption of fruits and vegetables, low-fat, normal body weight, exercise. What’s good is that a lot of modifications can be done.”
Helene Ragovin may be reached at helene.ragovin@tufts.edu.
