Cataracts

Chasing Away the Clouds

Crack open an egg and drop it into a hot frying pan. You'll see the egg white turn cloudy, then white, as normally clear proteins in the egg are irreversibly altered by the heat.

Well, something similar to that happens when you get cataracts. Proteins in the lens of the eye lose their crystal-clear properties, becoming yellowish, cloudy and about as easy to see through as a fried egg. Of course, cataracts take not seconds but many years to form. And it's not heat but cigarette smoking, a buildup of sugar in the lens (usually associated with diabetes) and especially years of exposure to sunlight that eventually pull the shades on vision for many people.

Many doctors now think that the main cause of cataracts is oxidative damage to cells in the eye's lens. Oxidative damage is the same chemical process that rusts iron and makes cooking oil turn rancid. In the lens, the oxidative process can occur as part of normal metabolism as well as in the presence of light, which creates harmful unstable molecules called free radicals. These free radicals grab electrons from your body's healthy molecules to balance themselves, causing an ever-escalating molecular free-for-all that ends up hurting perfectly innocent cells.

Nutrients Shield the Lens

The lens can partially protect itself from this free radical damage, and it relies on certain nutrients to keep its defense system strong. Vitamins C and E, beta-carotene (a precursor of vitamin A) and minerals such as selenium, zinc and copper--all components of antioxidant enzymes found in the lens--may all play roles in protection. Even B vitamins such as riboflavin and B₁₂ as well as an amino acid called cysteine may be involved, but evidence for these nutrients is very slim, says Randall Olson, M.D., professor and chairman of the Department of Ophthalmology at the University of Utah School of Medicine and director of the John A. Moran Eye Center, both in Salt Lake City.

"Not all of the facts are in, but the evidence to date is mostly positive that nutrients such as vitamins C and E and beta-carotene are helpful," Dr. Olson says. "And the evidence seems to indicate that these nutrients are synergistic, that they work best together."

In fact, several small studies suggest that people who take A ten-year nationwide study now in progress called the Age-Related Eye Disease Study is evaluating whether a mix of vitamins, including E, C and beta-carotene, really does help keep eyes crystal-clear. "Until the results of that study are in, we can't say for sure whether these nutrients are really helpful," says Emily Chew, M.D., medical officer in the Division of Biometry and Epidemiology at the National Eye Institute in Bethesda, Maryland.

In the meantime, here's what research shows may help slow the development of cataracts.

Take C and See

Researchers have known for some time that the lens of the eye can concentrate vitamin C. Concentrations of vitamin C in the lens and in the aqueous humor, the watery fluid surrounding the lens, are about 10 to 30 times the concentrations in other parts of the body.

"We're very interested in a possible protective effect, especially since vitamin C is a water-soluble antioxidant and the lens is composed mostly of water and proteins," says Allen Taylor, Ph.D., director of the Laboratory for Nutrition and Vision Research at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston.

In studies using laboratory animals, vitamin C seems to help protect the lens from oxidative damage from light, sugar and certain drugs, Dr. Taylor says.

And what about people? "It's possible that people are not getting enough vitamin C in their diets to make a difference when it comes to preventing cataracts," says Susan E. Hankinson, Sc.D., associate epidemiologist in the Channing Laboratory at Brigham and Women's Hospital in Boston. And there are a couple of studies that suggest vitamin C supplements can help protect against cataracts.

When Dr. Hankinson and researchers at the Harvard School of Public Health crunched numbers on nutrient intakes for 50,828 nurses, they found that women who had taken vitamin C supplements for ten years or more (average intake: 250 to 500 milligrams daily) fared better. Compared with women who never took supplements, the supplement takers had 45 percent less chance of developing cataracts bad enough to require surgery.

In another study, people taking 300 to 600 milligrams of supplemental vitamin C a day experienced a 70 percent decrease in risk compared with people who were not taking that much vitamin C.

"Our finding makes sense, because cataracts generally form over a long period of time," Dr. Hankinson explains. "It's reasonable to think that long-term use of preventive agents such as vitamin C would result in lowered risk."

Doctors who recommend vitamin C to people at risk for cataracts suggest from 500 to 3,000 milligrams a day. (Some people may experience diarrhea when taking more than 1,200 milligrams of vitamin C daily.) "Research has yet to determine an optimum amount of vitamin C to take to prevent cataracts, but studies do show that the concentration of vitamin C in the lens continues to increase as people move into the 500-milligram range," says Dr. Taylor.

It's true that many doctors believe vitamin C is harmless even in high amounts. But when it comes to the eyes, one researcher contends that it's best to stay below 3,000 milligrams.

"I've found that intakes of 3,000 milligrams or more of vitamin C are associated with retinal macular puckering and sometimes with increased risk of retinal detachment," says Ben C. Lane, O.D., director of the Nutritional Optometry Institute in Lake Hiawatha, New Jersey. High doses of vitamin C seem to make the gelatinous material inside the eyeball watery, which reduces pressure against the retina, allowing it to more easily pull away from the back of the eyeball, Dr. Lane says. (The retina is a light-sensitive area at the back of the eyeball that receives images.)

It may be wise to get at least some of your daily vitamin C from citrus fruits. That's because chemical compounds called bioflavonoids, which are closely related to vitamin C and are found in the white membranes of oranges and grapefruit, also seem to offer antioxidant protection and, Dr. Lane adds, may even be more important.

14-Carrot Eye Protection

We know. It's an old, old line, but the point is well-taken: The reason (well, maybe one reason) you've never seen a rabbit with glasses may indeed stem from this long-eared critter's penchant for carrots and perhaps spinach.

When it comes to cataracts, beta-carotene and plain old vitamin A may offer protection. At least that's what Harvard School of Public Health researchers found when, once again, they picked apart the diets of their much-studied nurses. They found that women with the highest beta-carotene and vitamin A intakes had a 39 percent lower risk of cataracts severe enough to require surgery than women getting the least beta-carotene and vitamin A.

It is possible that both beta-carotene and vitamin A may help prevent oxidative damage to the lens. Vitamin A itself is not an antioxidant. But, explains Dr. Hankinson, "it's possible that people who get enough preformed vitamin A in their diets have more beta-carotene and other carotenoids available to act as antioxidants, since these compounds may be converted to vitamin A only as the body needs them." In other words, if you're taking in enough vitamin A, your body won't need to use up beta-carotene to make the vitamin for you. Doctors who recommend vitamins suggest about 25,000 international units of beta-carotene daily.

Many doctors, including Dr. Hankinson, warn that it's too early in the research game to place your bets on any one supplement, such as beta-carotene, to prevent cataracts. Vitamin-rich foods seem to be important, too. "Even though we found that carrots offer protection, we found a stronger protective effect from spinach, which doesn't contain as much beta-carotene but has antioxidant compounds such as lutein and zeaxanthin," says Dr. Hankinson.

Best advice to date: Keep packing in those leafy greens as well as orange and yellow fruits and vegetables.

E Is for Eyes

What do wheat germ and sunflower oil have to do with healthy eyes? Both are good sources of vitamin E, an antioxidant nutrient that works its way into cell membranes and disarms free radicals before they have a chance to attack cells.

"Research in animals and test tube studies indicate that vitamin E may help protect the lens from oxidative damage from light, sugar and cigarette smoke," Dr. Olson explains.

In humans, the story seems to be the same. In one study, people taking 400 international units of vitamin E a day had half of the risk of developing cataracts compared with people who did not take vitamin E. In another, people whose blood levels of vitamin E were high had about half of the risk of developing cataracts compared with people with low blood levels.

"Vitamin E is a powerful antioxidant," Dr. Olson explains. "There's reason to believe that combined with other nutrients, it may help slow the progress of lens clouding."

You'd have to plow your way through bowls and bowls of wheat germ to get 400 international units of vitamin E, the amount found in some capsules. So supplementation is in order. "I recommend 400 international units a day," Dr. Olson says. The Daily Value for vitamin E is 30 international units, but most people get only about 10 international units a day from their diets.

The Case for Zinc

Doctors sometimes add a bit of zinc, an essential mineral, to their anti-cataract formulas. There's evidence that zinc is important for the function of the retina and that it may help prevent deterioration of the retina as we age. Plus the body needs zinc to make several antioxidant enzymes found in the eye, including superoxide dismutase and catalase.

Doctors who recommend zinc to prevent or slow cataracts call for a wide range, from 15 milligrams a day (the Daily Value) to 50 milligrams a day, the amount Dr. Olson recommends. Dr. Lane bases his initial dosage on an individual's zinc status, determined by testing. "It may be necessary to start a person at a fairly high amount, then cut back as his status returns to normal," he says.

One thing is for sure with zinc: More is not necessarily better, and doses exceeding 15 milligrams should be taken only under medical supervision. Too much zinc can deplete your body of copper, an essential trace mineral. You should get about 1 milligram of copper for every 10 milligrams of zinc. Even in fairly small amounts, copper can be toxic. Don't use long-term copper supplementation above the Daily Value of 2 milligrams without medical supervision, Dr. Lane cautions.

Selenium Adds Antioxidant Power

Doctors sometimes round out their antioxidant prescriptions with selenium, a mineral involved in the body's production of glutathione peroxidase, another protective enzyme found in the eye and other parts of the body.

Dr. Lane recommends selenium supplements only to people who have been found to be deficient in glutathione peroxidase activity or in red blood cell selenium or who have been subject to mercury poisoning. Dr. Olson does not recommend individual selenium supplements but does sometimes recommend multivitamin/mineral products that contain selenium, such as Icaps and Ocuvite (available in health food stores).

Doctors who recommend selenium supplements suggest 50 to 200 micrograms a day, no more. In even small amounts, selenium can be toxic, so don't take more than 100 micrograms daily without medical supervision.

If you're a fan of garlic, you'll be getting a healthy amount of selenium with each bite. Other selenium-rich foods include onions, mushrooms, cabbage, grains and fish.