Looking For Supplements That Aid Vision


by Linda Roach



Take a stroll down the vitamin aisle at your supermarket and you'll likely find a section where the vitamin or herbal formulas are labeled as "supporting eye health." The options are many: antioxidants, carotenoids, ginkgo, bilberry. It's a tempting place to stop if you're concerned with the common vision problems that accumulate with aging -- macular degeneration, cataracts, glaucoma, diabetic retinopathy.

      Yet there's not much to back up most of those uses. Even the Bible of alternative medicines using an evidence-based approach, Germany's Commission E report, has very little to say about whether antioxidants or other nutrients can help prevent the eye diseases of aging. And that's the biggest uncertainty for people who want to use supplements to preserve vision.
       Also of concern is whether a supplement that contains a lot of one nutrient could do your eyes harm by blocking others that are also important to eye health. This is particularly the case with carotenoids, the plant compounds like beta-carotene and lutein that are most commonly found in eye supplements.
       "There are over 600 carotenoids in the food we eat," says Dr. Donald S. Fong, a California ophthalmologist who has done research at the National Institutes of Health on the importance of nutrients in retinal diseases. "So if you supplement with high doses of any single one, you block the absorption of other carotenoids you may need. And, in addition, you might increase the risk of disease in other parts of the body."

       Dr. Fong is referring to two studies of vitamin A and beta-carotene, published in The New England Journal of Medicine in 1994 and 1996. Both found that smokers who took beta-carotene actually had a higher risk of lung cancer than those who puffed away without supplements.
       Fresh from that lesson, most ophthalmologists won't recommend specific nutrition supplements to their patients as a preventive. At the most, they say, a daily vitamin/mineral combination is adequate.
       The rest of the nutrients you consume in hopes of protecting your vision should come from "functional foods," they say. That is, eat your grains and oils for vitamin E, selenium and zinc; fruits for vitamin C and other vitamins; and dark green, leafy vegetables like spinach and kale for carotenoids.

       Why? Because people who have the highest blood levels of antioxidant vitamins (C and E) and carotenoids, such as lutein and beta carotene, are less likely to develop cataracts and age-related macular degeneration, according to long-term observational studies like the Nurses Health Study.

      Such research can implicate nutrition as the cause of this phenomenon -- but it can't say which nutrients are responsible or in what amounts. Nor do such studies translate into evidence that taking supplement pills will give your body the same protective effect that a nutrient-rich diet will.
       This was a key point in the April Institute of Medicine report that increased the national Recommended Daily Allowances for vitamins C and E and the mineral selenium. "Insufficient evidence" exists to recommend antioxidants as a preventive for eye and other chronic diseases, the report said. Nor is it clear that carotenoids, commonly touted as cell-protecting antioxidants, actually function as antioxidants when consumed. The report called for large, well-controlled studies to settle the issues.

       The National Eye Institute expects results by the fall of 2001 from one such project, the Age-Related Eye Diseases Study. The study assigned 4,700 individuals -- some with varying degrees of eye disease already -- to four supplement groups: zinc supplements; beta-carotene and vitamins C and E; a combination of all those nutrients; or placebo. Researchers are checking whether any of the groups develop fewer cataracts or cases of age-related macular degeneration, a retinal disease that is the leading cause of unavoidable blindness in elderly Americans.
       Other common eye diseases of aging are diabetic retinopathy and glaucoma. The former involves development of uncontrolled blood vessel growth on the retina, the flat area at the back of the eye where images fall before being sent to the brain. In glaucoma, high fluid pressure in the eye and other unknown factors cause deterioration of the optic nerve behind the retina, preventing good visual signals from reaching the brain.

       People with any of these diseases, or who have a family history they are trying to outrun, are the prime target for advertising and health-food store shelves touting the benefits of various "eye vitamin" supplements.
       Here is what is known about the ingredients that occur most commonly:

Lutein and zeaxanthinin
       These increasingly promoted carotenoids make up the macular pigment, located in the center of the retina where the finest vision occurs. Advocates of these nutrients suggest that taking supplements of them will help you build a thicker pigment layer, preserving vision as you age. A study at Boston's Schepens Eye Research Institute in 1998 showed that elderly people with thicker macular pigment reacted to light more effectively. But most ophthalmologists say the best way to get carotenoids is in food because the eye may require a mix of the 600 different carotenoids found in foods.

       This carotenoid is a precursor to vitamin A in the eye, which is essential to the biochemical cycle in which retinal cells adapt to the dark. Consequently, "eye vitamin" supplements often contain it. However, since blindness from vitamin A deficiency is only a problem in very poor countries, and the Institute of Medicine and others recommend against taking supplements except for outright deficiencies. In addition, it is the vitamin most often mentioned as toxic at megadoses (above 50,000 International Units daily).

      This derivative from the fruit of a small, alpine shrub also is showing up increasingly in eye preparations in health-food stores. The German Commission E report supports its use only for diarrhea or inflammation of mucous membranes. However, bilberry is used in other European countries, especially Italy, for microcirculatory disorders -- which many eye doctors believe is an underlying problem in some retinal diseases, glaucoma and diabetic retinopathy. Bilberry also is thought to aid the eye's rhodopsin cycle and thus improve night vision. In this country, it hasn't been studied either for effectiveness or for adverse effects.

Vitamins C and E
       The recent Institute of Medicine report increased the Recommended Daily Allowances of these vitamins, which many eye vitamin preparations include as cell-protecting antioxidants. The institute recommended 75 mg. of vitamin C daily for women and 90 mg. for men, with an extra 35 mg. daily for smokers. The RDA for vitamin E was set at 15 mg. from food, or 22 International Units for natural-source supplements (d-alpha-tocopherol) or 33 IU of synthetic E (dl-alpha tocopherol). For the first time, the Institute's RDA panel also set an upper safety limit for these vitamins: 2,000 mg. daily for C, 1,500 IU for natural E and 1,100 IU for synthetic E.

Zinc and selenium
      Both these minerals appear in many eye vitamin preparations because of evidence that they are essential to biochemical processes in the eye. Selenium is especially touted because it is known to function as an antioxidant elsewhere in the body, and advocates say this means it should help prevent damage to retinal cells from normal oxidative processes there. As with other supplements, the scientific evidence is lacking.

Ginkgo biloba
       Leading glaucoma specialist Dr. Robert Ritch, a clinical professor at New York Medical College and co-author of a standard text in glaucoma, tells his patients to take daily supplements of the herb ginkgo biloba. He believes the herb scavenges free radicals produced by oxidation and increases the blood supply to the optic nerve. It is this nerve connecting the eye and brain that deteriorates in glaucoma. However, the German Commission E report refers to gingko primarily for dementia, and no controlled studies of its effectiveness in the eye are planned.
       Citing European and Chinese literature on the herb, Dr. Ritch prescribes 120 mg. twice daily for two months, then 60 mg. twice daily indefinitely. (The only patients who don't get this advice are those on blood-thinners because of cardiovascular problems.)




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