Eating for Eye Health-New Research Sharpens the Focus

NORMALLY, the results of a single study don't lead researchers to make recommendations on whether people should change their habits. But a new study on macular degeneration, the leading cause of irreversible blindness in older Americans, has proven so promising that its authors are advising certain people to start taking high doses of vitamins C and E, beta-carotene, and zinc in hopes of slowing the advance of the disease. Still more new research says that high-dose C, E, and beta-carotene pills may also help prevent cataracts, which afflict more than half of all Americans age 65 and older.

The evidence for certain eating patterns to stave off eye disease is getting stronger, too. Scientists have known for some time that consuming a diet rich in fruits and leafy green vegetables seems to play a role in protecting eyesight. But research now bolsters the idea with a finding that higher intakes of a couple of substances found in produce--lutein and zeaxanthin--are correlated with higher levels of a substance in eye tissue that may provide protection against macular degeneration. Yet another just-published study adds one more dietary twist: Changing your fat-eating habits might also help prevent macular degeneration.

Macular degeneration
Supplements may buy some time

The new finding that taking supplement pills may forestall the advance of macular degeneration is a big one, because there aren't yet any proven treatments to slow or stop the disease. Researchers still don't know exactly how it starts, but over time, parts of the eye's macula (a tiny area at the retina's center), which are responsible for sharp vision, become diseased. As they break down, vision begins to blur. And as the breakdown progresses in stages, tiny blood vessels in the retina may begin to leak blood and fluid that cause even more damage. At that point, loss of vision can occur within weeks or months.

That's why the recent evidence on supplemental vitamins C and E, beta-carotene, and zinc is such big news. In an enormous effort coordinated by the National Institutes of Health, researchers at 11 eye centers around the country tested various combinations of those nutrients on some 3,600 people ages 55 to 80 for 6 years. The study, called the Age-Related Eye Disease Study, or AREDs, found that certain people with macular degeneration who swallowed one particular combination reduced their odds of the disease worsening by 25 percent.

The AREDs results were compelling enough that the study's authors recommend that everyone over 55 have an eye exam to check for the presence of eye abnormalities that indicate risk for macular degeneration. Those whose doctors determine that they're in the intermediate stages of the disease should consider following the study regimen: 500 milligrams of vitamin C daily, 400 International Units of vitamin E, 15 milligrams of beta-carotene, 80 milligrams of zinc, and 2 milligrams of copper--the last of which is to prevent the high doses of zinc from interfering with copper absorption. (Smokers are advised not to take beta-carotene because earlier research has suggested that large doses of supplemental beta-carotene may be harmful to them.)

Vitamins C and E and beta-carotene, all antioxidant nutrients, are thought to play a role in protecting the body against the advance of macular degeneration by neutralizing destructive substances called free radicals that can damage delicate tissue in the retina. As for zinc, more than a decade ago, a small study suggested that the mineral might also help prevent macular degeneration. Zinc is involved in metabolism in the retina.

To be sure, supplements are by no means a cure. But they provide a ray of hope for people who have macular degeneration because they could slow its advance. "Now we have a lot more evidence that vitamins do play a role, and the advanced stages of the disease could be prevented in about 300,000 people who are at the intermediate stages," says Johanna Seddon, MD, an eye expert at Harvard University who helped lead the AREDs research.

For prevention, research still points to foods
The AREDs study didn't provide any word on whether taking supplements might help to prevent macular degeneration in people, say, with a family history of the disease. But there has been a great deal of evidence that eating produce-rich diets may pay off in the long run. For instance, studies point consistently to diets rich in dark leafy greens, like spinach, kale, and collard greens, as protective. The connection appears to be that two substances in leafy vegetables and other produce, lutein and zeaxanthin, are found in the portion of the eye subject to damage from age-related macular degeneration.

Indeed, a recent review by Tufts researchers of 30 years' worth of scientific evidence has linked "generous intakes" of lutein and zeaxanthin from foods like spinach and broccoli with as much as a 40 percent reduction in macular degeneration risk. A just-published study also bolsters the idea that eating more of those healthful foods may translate into real results in the eye. Researchers in Indiana who gave eye exams to 280 people found that higher intakes of lutein and zeaxanthin in the diet were linked with higher levels of macular pigment in the eyes. ("Macular pigment" is just another name for the highly-concentrated deposits of lutein and zeaxanthin in the macula.) That's important, because macular pigment is what's believed to protect against macular degeneration. Researchers think that it may help to absorb high-energy ultraviolet light before it can damage the retina. It may also be that lutein and zeaxanthin function as antioxidants--as do vitamins C and E and beta-carotene--by deactivating destructive forms of oxygen that damage tissue in the retina over time.

Fat tagged as a culprit
Yet another new finding is that vegetable fats--the kind found in particularly high concentrations in processed, store-bought items like pies, cakes, cookies, and other snack foods--may also play a role in macular degeneration. Researchers from Harvard University, who compared the histories of some 350 people with advanced macular degeneration to those of 500 people without the disease, have found that those with the highest intakes of vegetable fat were more than twice as likely to have the disease as those with the lowest intakes.

Although vegetable fats, or oils, are generally thought of as the "good" kind (as opposed to saturated and trans fats), foods with high levels of vegetable fat tend to be greasy junk foods, like potato chips. But it's not the vegetable oils per se that appear to be the problem. When the Harvard researchers dug a little deeper into their data, they found that it was the ratio of certain fats in the diet that seemed to matter. People who ate less of a particular vegetable fat called linoleic acid, or omega-6 fat-found in the corn and sunflower oil used in packaged foods-and more in the way of omega-3 fatty acids-healthful fats found in foods like fatty fish, walnuts, flaxseed oil, and green leafy vegetables-were actually at reduced risk for macular degeneration.

To explain their finding, the Harvard researchers suggest that macular degeneration may share some of the same underlying mechanisms as heart disease, which has a clear connection with fat intake. For instance, omega-3 fatty acids are known to benefit heart health by reducing blood fats and making the blood less likely to clot. They may deliver similar benefits to blood vessels supplying the retina.

New View of Cataracts
There is a lot of overlap on what looks promising for cataracts and macular degeneration. For instance, many studies of cataracts, cloudy spots in the eye lens that cause progressive loss of vision, also provide evidence that the antioxidant vitamins C and E, and perhaps beta-carotene, lutein, and zeaxanthin, may play a protective role.

It makes sense when you consider that cataract is due in part to a process called oxidation, in which free radicals damage eye lens proteins over time. Oxidation alters the proteins in such a way that they clump together, thereby forming the cloudy spot. Unfortunately, unlike other cells in the body, lens cells are never replaced; they must last a lifetime. Researchers theorize that antioxidants may work in the lens to counteract the lens cell damage. Vitamin C may play a particularly important role, they believe, because it makes its way into and is concentrated within the lens. Indeed, vitamin C is concentrated in the lens in amounts 20 times higher than in the blood.

In one recent trial, led by researchers at the Harvard-affiliated Brigham and Women's Hospital in Boston, people with early age-related cataracts who took daily doses of vitamins C and E and beta-carotene for 3 years showed a "small deceleration" in cataract progression. The doses involved were quite high: 750 milligrams of vitamin C, 600 International Units of vitamin E, and 18 milligrams of beta-carotene. But as of yet, scientists aren't advising people to follow a similar regimen for cataract prevention. "It's premature to jump on those doses" as the answer, says Allen Taylor, PhD, who heads up the Nutrition and Vision Laboratory at Tufts. "The optimum levels are hardly defined."

Many other studies have linked produce-rich diets with lower cataract risk. The same Tufts review that linked leafy green vegetables with protection from macular degeneration also pointed to a 20 percent reduction in cataract risk. And a battery of research from the Nutrition and Vision Project (NVP), a joint effort by Tufts and Harvard investigators that looked at nutrient intake records and cataract formation in women in their 50s, 60s, and 70s, points to antioxidants in general, and vitamin C in particular.

For instance, in a recent NVP study that analyzed levels of more than a half-dozen nutrients in the diets of nearly 500 women over a 13- to 15-year period, vitamin C stood out. Women with the highest intakes of C, an average of 360 milligrams a day, had 70 percent lower odds of developing certain types of cataracts than women with the lowest intakes of 140 milligrams a day or less. But even those women in the second-to-lowest intake group, 140 to 180 milligrams, saw a reduction in odds of nearly half. And among those who'd taken C supplements, swallowing the pills for 10 years or more resulted in significantly reduced cataract odds as opposed to taking the pills for a shorter time or not at all.

Though those amounts of C may sound high (the Daily Value for vitamin C is 60 milligrams), it's certainly possible to get them through diets that contain the recommended five to nine daily servings of fruits and vegetables. To take in 200 milligrams, for example, you'd need to eat a half-cup of broccoli, 6 ounces of orange juice, ¼ cup of chopped green pepper, and a cup of cantaloupe chunks. Add a baked potato and a kiwifruit, and you're up to 300.

Even with the abundance of evidence pointing to vitamin C, it's a difficult task to tease out exactly which nutrients, in which amounts, may be at work in protecting against cataracts. Still, "if you look at the totality of the data, there's general agreement that the antioxidants have benefit," says Dr. Taylor. "But it would have to be long-term, maybe 10 years or so." Since early cataract probably begins at about 45 years of age, people in their 30s should pay attention to their diets--eating plenty of fruits and vegetables. If that's not possible, supplements may be in order

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