Making Sense of Contradictory
Reports about Fruits, Vegetables, and AMD
Possible
Beneficial Effect of DHA on
Retinitis Pigmentosa
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(Foundation Fighting Blindness) CBS news and other media outlets recently reported on findings by researchers which might appear to contradict the June 2004 FFB InSight story entitled, "Colorful Foods and AMD Prevention: A possible role for lutein and zeaxanthin." The FFB InSight article described research indicating that fruits and vegetables rich in the nutrients zeaxanthin and lutein appear to decrease the risk of developing age-related macular degeneration (AMD). The CBS news report said that fruits, but not vegetables, appear to reduce the risk of AMD. Readers should realize that researchers do not have a conclusive answer about the relationship of nutrients to AMD prevention and, although some evidence is compelling in one direction or the other, much more research needs to done before we can say conclusively what foods or vitamin supplements protect against AMD. The CBS news report was based on an article published in a recent issue of the medical journal, Archives of Ophthamology (June 2004, vol. 122, pgs. 883-892). The authors, all experts in the field of nutrition and AMD compared facts about fruit and vegetable intake, reported by tens of thousands of participants, with the incidence of cases of AMD during a period of up to 18 years. Reading the article reveals additional important findings that are not mentioned in the news story. Not only did fruits and not vegetables impact AMD, but it was only bananas and oranges that showed any effect. This puzzled the researchers because many other fruits are rich in lutein and zeaxanthin. Then, too, so are many vegetables. They propose a number of possible explanations for the findings. For example, maybe it's not lutein and zeaxanthin in the bananas and oranges that infuse them with protective qualities; it could be other nutrients like flavonoids, isothiocyanates, phenols, fiber, folate, and potassium. Or maybe the participants, all of whom were in medical professions, had a healthy lifestyle that protected them against AMD in other ways. The research on both sides is important because it reminds us about the complex process involved in making discoveries and the need for continued research to come to definitive conclusions.
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Beneficial Effect of DHA on Retinitis
Pigmentosa FFB-supported scientists recently reported that daily nutritional supplements of a fatty acid called DHA appear to have the potential to help patients with X-linked retinitis pigmentosa (XLRP). Results were encouraging but not conclusive by statistical measures. However, the outcome is important enough that researchers are continuing to study the effect of DHA on XLRP. DHA is shorthand for docosahexaenoic acid. It is a fatty acid and is normally contained within membranes of most tissues of the body. Within the retina and brain, DHA is present in much higher concentrations than elsewhere. XLRP is a progressive form of retinal degeneration caused by one of several different genetic defects. It occurs in about 1 of 100,000 people in the U.S. The progression of the disease varies from person to person, even in members of a single family where RP is caused by the indentical gene defect. Characteristic symptons of XLRP include (i) night blindness in early childhood caused by the loss of rod photoreceptor cells (ii) tunnel vision in the 2nd or 3rd decade of life because of progressive loss of cone receptor cells, and (iii) sometimes, total blindness. Other factors such as diet, environment and stress may influence the course of the disease. DHA is a common fatty acid in fish oils, especially in cold water fish like wild salmon, tuna, mackerel, sardines, shellfish, and herring. Its levels in humans and laboratory animals can be measured in blood. A deficiency of DHA in rats, guinea pigs, and other experimental animals, and human infants and adults, has been associated with low retinal function. Among the scientists involved in the XLRP-DHA research are Dr. David G. Birch and Dr. Dennis Hoffman of the Retina Foundation of the Southwest and the University of Texas Southwestern Medical Center. Dr. Birch is a member of FFB's Scientific Advisory Board. In a study of over 40 male patients with X-linked retinitis pigmentosa, patients received capsule supplements of DHA or placebo capsules (containing no actual DHA) and were followed for a 4-year period. After 6 months of DHA supplementation, the blood concentrations of DHA in study subjects had increased more than two-fold, and remained elevated during the study. This study was reported in the April 2004 issue of the American Journal of Ophthalmology. The results were not conclusive with respect to slowing the rate of retinal degeneration. One of the problems was that loss of cone function was less in the placebo-treated subjects than usual. Nevertheless supplemental analyses were encouraging in that the results provide "preliminary evidence for a DHA benefit and a direction for subsequent investigations." The FFB recommends alway conferring with your health care provider before using any nutritional supplements or other forms of complementary or alternative medicine.
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Medicare Legislation News The Medicare bill, passed by Congress in late November, legislates a one-year study to produce recommendations by January, 2005 for legislative action �providing for payment for vision rehabilitation services furnished by vision rehabilitation professionals.� Other legislation expected to be passed this year would establish a funded, five-year demonstration project to provide vision rehabilitation services where they are most needed: at home and in the community.
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