It seems like magic. Our eyes transform light into nerve signals that somehow tell our brains what we see. But as we get older, the magic often starts to fade.
One of two American aged 65 or older has a cataract, a cloudiness in the eye’s lens. Age-related macular degeneration (AMD) is a breakdown of the center of the retina, called the macula. One of four people 65 and older has early signs of AMD, the leading cause of new cases of blindness in that age group.
Is declining eyesight inevitable, or can antioxidants like lutein and vitamins C and E-and possibly zinc or fish or omega-3 fats-keep our eyes from failing?
Food choices may help prevent or stave off some vision disorders, but fixing them is another matter, according to Dr. Julie Mares Perlman, an associate professor of ophthalmology and visual sciences at the University of Wisconsin at Madison. She is the principal investigator on two large studies on diet and eye disease.
“The likelihood that any one nutrient will prevent a large proportion of cataracts or macular degeneration is still a dream,” she says. “It’s more likely that a combination of nutrients or diets rich in many of them will have the largest benefit.”
The cost of cataracts
Once you have a cataract, surgery is the only way to get rid of it. And until that surgery, vision will continue to decline.
“The last time somebody counted, cataract surgery was the largest single item in the Medicare expenditure budget,” Perlman says. “And as the population ages, cataract surgery will become an even greater burden, because the number of people over 75 will triple over the next 50 years.
“If we could delay a person’s need for cataract surgery by 10 years through preventive measures, we could cut in half the number of yearly cataract surgeries.”
Age is the strongest risk factor for cataracts, Perlman says, but genetics are probably involved. Sun exposure may increase the risk, as do smoking and diabetes.
As far as nutrients playing a role in cataract prevention, she says, “The evidence is strongest for antioxidants like vitamins E and C and for two carotenoids–lutein and zeaxanthin. But we’re still in the early stages of investigating those links.
“We know that oxidative damage from light produces free radicals that can cause cloudiness in the lens. Antioxidants may protect against oxidative damage by acting as scavengers for the free radicals.”
Studies have shown that vitamin E can slow the rate at which animals get cataracts. Some studies-like the Baltimore Longitudinal Study of Aging, the Lens Opacities Case-Control Study, and the Beaver Dam Eye Study of people in a Wisconsin town-find higher rates of cataracts among people who get little vitamin E from food or have low levels of E in their blood. “But the data are inconsistent,” Perlman says.
With vitamin C, higher levels protected against lens damage in animal studies, Perlman says, “and we can increase vitamin C in the lens with supplements.”
In humans, an increasing body of evidence indicates that vitamin C protects against cataracts. For example, in a study of 247 nurses, the prevalence of early cataracts was 77 percent lower in women who had taken vitamin C supplements for at least 10 years.
“But we still don’t know whether that’s because people who take vitamin C are also getting other nutrients or leading a healthier lifestyle,” she says.
Much the same story applies to lutein and zeaxanthin, but there’s a twist.
“The interesting thing about these sister pigments-from now on I’ll just say lutein to refer to them both-is that they’re the only carotenoids that are found in large quantities in the lens,” Perlman says.
“We also know that lutein can absorb ultraviolet light in the blue range, which could explain how those carotenoids might protect the lens. Or, lutein may simply act as an antioxidant to prevent light from damaging the lens.
“The results from human studies are more consistent for lutein than for vitamins C or E. But so far, there are only three studies on lutein.”
But the studies were large, and they followed people for years: One tracked 77,000 nurses, another dealt with 37,000 health professionals, and the third consisted of 1,400 people in Beaver Dam.
In two of the studies, the risk of cataract surgery was only 20 percent lower in people who consumed more lutein. But those researchers looked only at surgery, not new cataracts. “A lot of things affect whether a person has cataract surgery. People who are more educated might have healthier diets and get cataracts taken out at an early stage, so those things could have masked a potentially important association between lutein and cataracts.”
In contrast, in Beaver Dam, there was 50 percent lower risk for new cataracts among people who had had diets higher in lutein.
Again, she says, “we don’t know if it’s the lutein or something else about their diets or lifestyles that lowered their risk.”
One study, the Blue Mountain Eye Study, suggests a link between sodium intake and cataract risk, “But we have to be cautious about the finding because it’s the first time we’ve seen an association between sodium and cataracts,” she says.
At this stage, the advice for people intent on avoiding cataracts tends to mirror that for overall good health.
“If you look across the body of research, many studies suggest that people with healthy diets are less likely to have or get cataracts. Because we haven’t nailed down the nutrients that are responsible, it’s prudent to eat diets that are rich in most vitamins and minerals.”
And that’s easily accomplished by eating more fruits and vegetables and fewer nutrient-poor, calorie-dense foods like snacks.
“It’s fairly boring advice,” Perlman says, “but it’s important.”
Multivitamins and supplements are at best second best, because “we don’t know how well the nutrients in multis are taken up by the body, and multis don’t provide all of the chemical forms of nutrients in food that might he helpful.” For instance, the type of vitamin E found in food, and in eye tissue, is not the same as that used in vitamin E supplements, and evidence suggests that the pill form of vitamin E actually reduces the vitamin E in human tissue.
What about the macula?
Solid recommendations on dietary defenses against macular degeneration are similarly elusive so far: Observed links between nutrient intake and rates of the disease don’t yet allow people like Perlman to write a prescription.
The macula is involved in seeing fine details and in seeing what’s in the center, not around the edges, of your view. And partly because so much light strikes the macula, its metabolism produces free radicals at a faster clip than the rest of the body. “The macula is also high in polyunsaturated fatty acids, which are particularly vulnerable to attack by free radicals,” Perlman says.
Which would seem to make antioxidants prime candidates in the fight against macular degeneration.
“Because lutein absorbs light and quenches free radicals, and because lutein is so concentrated in the macula, we think that eating high levels might protect against AMD,” Perlman says. “Also, you can increase lutein levels in the retina by taking lutein pills or eating foods like spinach or corn.”
But the ability to enrich the retina with lutein varies from person to person. “We have yet to figure out why some people don’t respond to changes in the diet and some do.”
Age-related macular degeneration can cause blindness because it ultimately results in the loss of cones in the center of the macula. There is no cure once the cones have been lost.
Women may be at higher risk than men. Smokers and people with a family history of AMD are also more likely to get the disease. Scientists are investigating blood cholesterol, blood pressure and heart disease as risk factors.
Studies of the effects of zinc, vitamin E and vitamin C on AMD so far have been inconclusive, Perlman says. Fish fats and other omega-3s may turn out to help, insofar as they protect against inflammation and cardiovascular disease, which are thought to promote AMD.
“We’re early in the investigation of this theory, but it’s promising.”
Ability of diet to protect eyesight is limited but promising, researcher says
THE LUTEIN LIST
How much lutein is enough? In one of the largest studies, people who consumed roughly 14,000 micrograms (mcg) a day of lutein and zeaxanthin, largely from leafy green vegetables, had a lower risk of cataracts than people who consumed roughly 2,000 mcg a day. The following are combined counts, in micrograms, of lutein plus zeaxanthin.
– Kale, cooked (1/2 cup) 10,270
– Collard greens, cooked (1/2 cup) 7,690
– Spinach, cooked (1/2 cup) 6,340
– Turnip greens, cooked (1/2 cup) 6,080
– Spinach, raw (1 cup) 3,580
– Broccoli, cooked (1/2 cup) 1,740
– Corn, cooked (1/2 cup) 1,480
– Lettuce, romaine (1 cup shredded) 1,480
– Zucchini, raw (1/2 cup) 1,320
– Peas, canned (1/2 cup) 1,150
– Brussels sprouts, cooked (1/2 cup) 1,010
– Orange juice, from concentrate (1 cup) 340
– Baby carrots (8) 290
– Lettuce, iceberg (1 cup chopped) 190
– Tomato, raw (1/2) 80
