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Studies Point to Diet's Effects on Eyes

Fish oil, vitamins C and E among nutrients in spotlight Healthy Living:
YOUR TUESDAY GUIDE TO MEDICINE AND HEALTH CARE
Jane Brody - New York Times
Tuesday, April 3, 2001


We all grew up knowing that carrots are good for our eyes. Carrots, among other deeply colored vegetables and fruits, are rich sources of beta carotene, the plant-based building block for vitamin A, which is required to form rhodopsin, the visual pigment that allows people to see in the dark.

But now medical science is learning a lot more about the influence of diet on vision. It isn't just carrots and vitamin A. Other potentially important nutrients include two related carotenoids, lutein and zeaxanthin; vitamins C and E; and docosahexanoic acid, or DHA, found primarily in fish oil.

While evidence for the effects of these nutrients on visual development and prevention of sight-robbing eye diseases is not conclusive, strong hints from recent research may justify dietary improvements. Even if some of those changes turn out to be only minimally helpful to the eyes, they have other health benefits.

DHA for developing vision

Evidence for the role DHA plays in visual development comes from premature babies. Infants born eight or more weeks early arrive almost fat-free, lacking both a reserve of stored energy and the fatty acid DHA, which is essential for normal visual (and brain) development.

DHA normally accounts for more than one-third of the fatty acids in the retina of the eye as well as in the brain's gray matter. The retina develops rapidly in the final months of pregnancy and in the first six months of infancy.

Fetuses begin to acquire large amounts of DHA only in the last three months of pregnancy. Unless a premature baby is fed breast milk (which naturally contains DHA) or formula fortified with DHA, the child's visual acuity is likely to be compromised.

Nearly a decade ago, Dr. Susan Carlson of the University of Tennessee at Memphis described the benefits of DHA supplementation in 67 infants born about two months early. When compared with premature babies given standard formula, those who received formula fortified with DHA showed gains in visual acuity for about four months.

In a study by Dr. Eileen Birch at the University of Texas Southwestern Medical Center in Dallas, preterm babies fed formula fortified with fish oil developed visual acuity similar to that of term infants and preterm infants fed breast milk.

A study published last year in The American Journal of Clinical Nutrition by Cathy Williams found that full-term infants also benefit visually from DHA. Children who were breast-fed for four months were more likely to achieve a high degree of stereoscopic vision at age 3 1/2 than were those who were not breast-fed. Also, children whose mothers ate fatty fish during pregnancy developed better stereoscopic vision.

For breast-fed babies, the amount of DHA in breast milk depends on the mother's diet. The best dietary sources of DHA are cold-water fish such as mackerel, Atlantic salmon and cod, bluefish, halibut, herring, sockeye salmon, striped bass, tuna and flounder. Two to three servings per week can maintain adequate levels of DHA in an adult. Pregnant women who do not eat fish may take a daily DHA capsule.

Two common sight-robbing disorders, cataracts and age-related macular degeneration, have been linked in several studies to dietary deficits of nutrients. Maintaining an adequate intake of these nutrients may not prevent the eye disorders, but it can't hurt.

Age-related eye disorders

Nearly everyone who lives long enough develops cataracts, a clouding of the eye's lens that reduces the ability to see clearly. The main cause is believed to be oxidative damage by so-called free radicals caused by exposure to sunlight. Thus, antioxidants, which act as scavengers for free radicals, are believed to be protective.

One antioxidant nutrient, vitamin E, occurs naturally in the lens, and in animal studies, supplements of vitamin E have slowed the rate at which cataracts form. In several studies in people, notably the Baltimore Longitudinal Study of Aging, the Beaver Dam (Wis.) Eye Study and the Lens Opacities Case-Control Study, higher rates of cataracts occurred among those whose intake of vitamin E was low.

Vitamin C, another antioxidant found in the lens, has also prevented cataracts in animals. In a study of 247 nurses, those who took vitamin C supplements for at least 10 years had a rate of beginning cataracts 77 percent lower than those who took little or no vitamin C. It's not possible to say for sure that the vitamins themselves were protective and not simply a reflection of a healthier lifestyle.

The strongest evidence for eye benefits from dietary ingredients involves the carotenoids lutein and zeaxanthin, found in large amounts in the lens and retina. Lutein may help prevent cataracts through its ability to absorb damaging ultraviolet light, blocking oxidative damage.

Perhaps even more important, these carotenoids may prevent and even partly reverse otherwise untreatable damage to the macula, the area in the center of the retina that allows people to see whatever is in the center of their visual fields. People with advanced macular degeneration cannot see faces, read, watch television or drive.

Lutein and zeaxanthin are most prominent in dark green, leafy vegetables. Some experts recommend eating at least half a cup of one of these cooked vegetables daily.

VEGETABLES FOR VISION
A recent study showed that the consumption of 14,000 micrograms of lutein and zeaxanthin a day may help protect against cataracts. Foods high in those nutrients:
Cooked
( 1/2 cup).............. Micrograms
Kale........................ 10,270
Collard greens................7,690
Spinach...................... 6,340
Turnip greens................ 6,080
Broccoli......................1,740
Corn..........................1,480
Brussels sprouts..............1,010
Green beans.................... 440
Okra............................310
Raw......................Micrograms
Spinach, 1 cup................3,580
Zucchini, 1/2 cup............1,320
Squash, 1/2 cup................190
Tomato, 1/2 cup................ 80
Cabbage, 1/2 cup................50
Other....................Micrograms
Romaine lettuce, 1 cup........1,480
Peas, 1/2 cup................1,150
Orange juice, 1 cup............ 340
Baby carrots, 8................ 290
Iceberg lettuce, 1 cup..........190
Sources: U.S. Department of Agriculture; Center for Science in the Public Interest


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Date last modified August 5, 2001