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EarthSave promotes a shift toward a healthy plant-based diet.
Vol 19 No. 3
June 2008

Keep Your Eyes on those Leafy Greens

By Karen Ravn

Dismiss it as boring if you’d like, but “rabbit food” could be just what the doctor orders at your next ophthalmologist’s visit.

Eating the right vegetables, it now appears, may help to ward off some life-changing diseases such as cataracts and age-related macular degeneration, conditions you might otherwise come eye to eye with as you get older.

Surprisingly, despite their reputation, carrots are probably not near the top of the list. Certainly, the vitamin A they’re full of is necessary for eye health, says Dr. Michael Marmor, an ophthalmology professor at Stanford University School of Medicine. “But people are generally not vitamin A deficient in our society, and a high dose doesn’t do any more good.”

The most useful vegetables, according to new research, seem to be the leafy green ones -- such as spinach, kale and collard greens -- which are rich in the antioxidant carotenoids lutein and zeaxanthin.

These are also the only carotenoids found in measurable amounts in the eye, says Bill Christen, a professor of medicine at Brigham and Women’s Hospital in Boston and Harvard Medical School. “That adds credence to the idea that they could be of benefit,” he says.

Christen is lead author of a new study published this month showing that people who eat diets high in lutein and zeaxanthin are less likely to develop cataracts than others whose diets included less of those nutrients. A second new study by Australian scientists that is to be published next month, found similar results for age-related macular degeneration.

But while these studies show a diet-eye health relationship, they do not directly demonstrate cause and effect. Only one study to date has shown specific nutrients can cause reductions in risk for eye disease.

In that 2001 study, a high-dose combination of zinc and several antioxidants (not including lutein and zeaxanthin) lowered the risk of advanced macular degeneration and the vision loss that goes along with it.

Supplements based on that formula are now on the market. Designed for people who already have macular degeneration and are at high risk for having the disease progress to an advanced stage, these products contain zinc and antioxidants in amounts far exceeding their recommended dietary allowances. “They should be taken only on the recommendation of an ophthalmologist,” Marmor says.

But many experts recommend that people whose eyes are healthy should take supplements with ingredients that stick closer to recommended amounts such as a multivitamin that also contains lutein, zeaxanthin and zinc.

“It makes perfectly good sense to be taking a prudent amount of nutrient supplements, along with eating a healthy diet, in order not to have problems when you’re older,” says Dr. Roger Steinert, professor and vice chair of ophthalmology at UC Irvine.

“There’s no downside, and there’s good evidence it can help,” says alternative health guru and author Dr. Andrew Weil, founder and director of the Program in Integrative Medicine at the University of Arizona’s Health Sciences Center in Tucson. “I would recommend that people start from an early age . . . certainly in their teens.”

A look at vision loss

Cataracts cloud the eye’s lens and interfere with vision by blocking light from reaching the retina. “The lens is a bag of proteins,” Steinert says. “Cataracts develop when the proteins become disorganized,” similar to what happens when you fry an egg and the clear part becomes opaque white. Cataracts can be treated with surgery to replace affected lenses. The procedure is highly successful.

Age-related macular degeneration affects the retina. In advanced stages, it destroys sharp, straight-ahead vision, leaving people unable to read, drive or even recognize a friend’s face. In one form known as “dry” macular degeneration, vision loss sometimes occurs because light-sensitive cells break down in the macula, a yellow spot near the center of the retina.

Alternatively, in the much less common “wet” form, leaky blood vessels grow under the retina where they don’t belong. In either case, little can be done to repair the disease’s damage over the long term.

Similar traits, therapy

Different as they are, cataracts and macular degeneration share similarities. Both are age-related, have genetic components and are thought to result, in part, from oxidative damage caused by light.

Lutein and zeaxanthin might help prevent both.

In one new study, published in this month’s issue of Archives of Ophthalmology, Christen of Brigham and Women’s hospital led a team that analyzed the diets of more than 35,000 female health professionals who in 1993 had enrolled in an earlier research program, the Women’s Health Study, and were then tracked for an average of 10 years.

During that time, 2,031 of the women, who were all 45 or older when they enrolled, developed cataracts. When Christen’s team divided the women into five groups based on their estimated lutein and zeaxanthin consumption, they found that those in the top group (who consumed about 6.7 milligrams of the antioxidants a day in food and vitamins) were 18% less likely to develop cataracts than those in the lowest (who got about 1.2 milligrams).

The other new study, which is to be published next month in the journal Ophthalmology, analyzed data from 2,454 Australians who were 49 or older when they enrolled (from 1992 to 1994) and were re-examined after five or 10 years, or both.

Led by Dr. Jennifer Tan, a professor at the University of Sydney and Westmead Hospital in Sydney, researchers divided the participants into three groups according to how much lutein and zeaxanthin they consumed in their diets. Those in the top group were only about one-third as likely to develop wet macular degeneration as the rest of the participants.

Those above the median in consumption were only about two-thirds as likely as those below the median to develop certain forms of drusen, yellow deposits under the retina that are found in beginning and intermediate stages of macular degeneration that can increase the likelihood of developing an advanced form.

The Australian study also found that zinc was associated with a lower risk of developing macular degeneration. When researchers divided the participants into 10 groups according to how much zinc they consumed in their diets and in supplements, those in the top group were about half as likely as the others to develop any form of the disease.

This finding supported one from an earlier investigation, the 2001 Age-Related Eye Disease Study, a seven-year clinical trial sponsored by the National Eye Institute. In that randomized controlled study, people at high risk of developing advanced macular degeneration lowered their risk by about 25% when they took a high-dose combination of zinc and the antioxidants vitamin C, vitamin E and beta carotene. Those people also lowered their vision loss risk by 19%.

Participants who took either zinc alone or antioxidants alone also lowered their risk of developing advanced macular degeneration, but not as much.

The nutrients, alone or in combination, did no apparent good for people who showed signs of, at most, early stages of the disease. But because progression of the disease is slow, the seven-year trial may not have been long enough to reveal helpful effects, says Dr. Abdhish Bhavsar, director of clinical research at the Retina Center and attending surgeon at Phillips Eye Institute, both in Minneapolis. “If patients could be followed for a very long time, it’s possible that effects would be found,” he says.

The nutrients also had no effect on the development of cataracts.

The study did not include lutein and zeaxanthin among its antioxidants because they weren’t commercially available then, says Dr. Emily Chew, deputy director of the Division of Epidemiology and Clinical Research at the National Eye Institute. Chew is now leading Age-Related Eye Disease Study 2, a clinical trial that is adding lutein and zeaxanthin as well as omega-3 fatty acids to the nutrient combination used in the first study. Again, the objective is to see if the nutrients can lower risk of advanced macular degeneration.

Though both new studies help to paint a picture of nutrients as beneficial for eye health, they also blur things a bit.

In the cataract study, participants who consumed the most vitamin E were less likely to develop cataracts than those who ate the least. But in the Age-Related Eye Disease Study, antioxidants -- including vitamin E -- had no effect on cataracts.

In the macular degeneration study, both beta carotene and vitamin E were associated with an increased risk of late-stage disease. But in the Age-Related Eye Disease Study, both were included in the antioxidant combination that lowered the risk.

Even if vitamin E proves to be useful in preventing or mitigating eye disease, there are reasons to be cautious about taking it in high doses, Steinert says. For example, the prime ages for worrying about eye disease are also prime ages for worrying about cholesterol. And vitamin E has been shown to interfere with the effects of cholesterol-lowering statins.

Preventive measures

Some factors that lead to eye disease can’t be avoided. People can’t help but get older, and they can’t change their genes. Still, there are steps that improve the odds of keeping eyes healthy.

People do themselves one big favor by not smoking. Smoking can lead to cardiovascular disease, which can have drastic effects on the retina’s delicate blood supply.

They can do themselves another good turn by minimizing exposure to light. “Sunglasses are the sunscreen for the eyes,” Steinert says.

And more and more, it seems that people can delay or prevent eye disease by eating the right nutrients in the right amounts, although scientists still have a ways to go before they know just what those are. It can’t hurt, they say, to eat more leafy green vegetables. Taking a multivitamin is another no-risk strategy with possible eye-health returns. And if taking a vitamin, it might as well be one with lutein, zeaxanthin and zinc.

It’s not clear whether supplements can help ward off eye disease or merely slow progression after it starts, and partly for that reason experts don’t all agree when it’s best to start with a supplement regimen. Some, such as Chew, hesitate to recommend starting before developing early stages of disease because there are no clear data suggesting it will help before then. Others, such as Weil, think there’s no time like now, whether you’re 15 or 50.

Weil has been taking a blend of antioxidants for two decades. At 65, he says his eyes are exceptionally healthy.

“It’s true that I don’t wear reading glasses,” he says. “And that’s unusual. But I don’t know that I can attribute that to taking antioxidants.”