News You Can Use: Can an Apple (or Orange or Banana) a Day Keep the Ophthalmologist Away?
Age-related macular degeneration (AMD) is the leading cause of untreated vision loss among persons 65 years and older and accounts for 45% of all visual disability in the United States.1 This condition usually has significant adverse effects on quality of life.2 As the US population continues to age, the number of Americans with AMD is expected to increase.3
RISK FACTORS
Because pharmacologic and surgical treatment options for AMD are costly, are limited in scope and efficacy, and may result in complications as severe as end-stage disease (scarring of the macula), prevention of AMD is desirable. Modifying or eliminating risk factors may be helpful. Besides older age, unmodifiable risk factors include family history, female sex, and ocular characteristics such as light-colored irides.4 Several genes have been identified for diseases with features that overlap with those of AMD, but none of these genes account for a significant percentage of cases of AMD.
Modifiable risk factors include smoking; cumulative exposure to sunlight or short-wavelength blue light; longterm use of photosensitizing medications; excessive intake of dietary fat; obesity; hypertension; lack of exercise; and other cardiovascular disease risk factors, such as elevated cholesterol levels.4-7
DIETARY INTERVENTIONS: CLINICAL TRIAL RESULTS
Dietary modification and supplementation may decrease the risk of AMD. The Eye Disease Case- Control Study showed that AMD was less likely to develop in patients whose diets were rich in green leafy, yellow, and orange vegetables—that is, foods with high levels of antioxidant carotenoids.8 In a pilot study, zinc supplementation was found to reduce the risk of AMD-associated vision loss.9 Subsequently, the Age-Related Eye Disease Study (AREDS), a large, longterm, multicenter, randomized trial sponsored by the National Eye Institute, showed that supplementation with highdose vitamins C and E, beta-carotene, zinc, and copper reduced progression to advanced AMD by 25% during the course of 5 years among those with signs of intermediate or advanced disease in one eye.10
In a more recent study, investigators examined the effects of antioxidant vitamin and carotenoid supplements, as well as fruits and vegetables known to be rich sources of antioxidants, on the development of AMD.11 They followed the diets of 77,562 women for up to 18 years and 40,866 men for up to 12 years. The participants were at least 50 years old and had no signs of cancer or any form of AMD at baseline. During the course of the study, early, or “dry,” AMD was diagnosed in 329 women and 135 men (based on the presence of drusen or retinal pigment epithelial changes). Neovascular, or “wet,” AMD was diagnosed in 217 women and 99 men (based on retinal pigment epithelial detachment, choroidal neovascular membrane, or disciform scar). AMD was diagnosed when patients’ visual acuity deteriorated to less than 20/30.
Wet AMD was 36% less likely to develop in those who consumed 3 or more servings of fruit per day than it was in those who consumed fewer than an average of 1.5 servings per day. Among the fruits studied, only oranges and bananas showed a statistically significant protective effect. The effect appeared to be similar for men (43% decreased risk) and women (33% decreased risk).
No protective link was found between fruit consumption and dry AMD, which may have a cause other than wet AMD. A relationship with dry AMD might have been identified had the examiners used additional criteria to measure for this condition, such as contrast sensitivity function and glare recovery. 12,13 Consumption of vegetables, carotenoids, or antioxidant vitamins was found not to be strongly related to a reduced risk of either dry or wet AMD.
The Lutein Antioxidant Supplementation Trial (LAST) was a prospective, 12-month, randomized study involving 90 patients with dry AMD.14 Lutein is the primary dietary carotenoid xanthophyll pigment responsible for macular pigment optical density; it protects against AMD by absorbing light and eliminating free radicals.15 Lutein intake and high macular pigment optical density are believed to play both preventive and therapeutic roles in optimal eye health.16 The researchers found that patients who took lutein supplements improved in several objective measures of visual function. Patients also experienced an increase of approximately 40% in macular pigment optical density, whereas those who took placebo experienced no increases in any of the domains studied.
In a presentation at the 2004 meeting of the Association for Research in Vision and Ophthalmology, a new analysis of baseline data collected in AREDS participants suggested that lutein protects against both wet and dry AMD.17
A POSSIBLE ROLE FOR STATINS
The progression of dry AMD to the more severe wet form usually leads to severe deterioration in a patient’s vision. Preliminary evidence from a recent retrospective study of persons with AMD who had taken statins suggests that these drugs reduce the risk of progression from dry to wet AMD.18 Participants with the wet form of AMD were statistically less likely to have used statins for at least 6 months than those with dry AMD. The researchers also found that patients with wet AMD were significantly more likely than those with dry AMD to have higher serum triglyceride levels and lower serum high-density lipoprotein cholesterol levels and more likely to be current smokers. Patients with wet AMD were less likely to be aspirin users than those with dry AMD. The researchers concluded that evidence from this study supports the hypothesis that a common mechanism is responsible for both cardiovascular disease and wet AMD.