Eating a Variety of Colorful Fruits and Vegetables May Protect Against a Leading Cause of Blindness
By Ben A. Shaberman
The old adage “carrots are good for your eyes” holds a lot of truth. Carrots are rich in beta carotene, which your body converts into vitamin A—a nutrient essential to the biochemical process in your retina that enables you to see. However, experts believe your retinas might be even better off if you ate not only carrots but a wide variety of fruits and vegetables as well.
Recent studies suggest that eating a diverse mix of colorful fruits and vegetables, which are good sources of antioxidants, may help protect against a vision-robbing retinal condition called age-related macular degeneration (AMD). In the United States and much of the Western world, AMD is the leading cause of legal blindness in individuals who are 55 years of age and older. Approximately 9 million Americans are affected by AMD, and that number is expected to double by 2020 because of the aging population.
AMD is characterized by the build-up of drusen, yellowish deposits comprised of fats and proteins, under the central region of the retina known as the macula. The accumulation of drusen can lead to the dry form of AMD. Though dry AMD can sometimes cause vision loss, the condition puts people at increased risk for the wet form of AMD, which more frequently leads to rapid and severe loss of central vision. In wet AMD, unhealthy, leaky blood vessels grow under the macula, causing it to degenerate. Most current treatments for wet AMD involve injections into the eye to halt unhealthy blood vessel growth. There is no known cure for either form of AMD.
In an investigation called “A Dietary Antioxidant Index and Risk for Advanced Age-Related Macular Degeneration in the Age-Related Eye Disease Study” conducted by the National Eye Institute, researchers evaluated the antioxidant intake of more than 1,700 individuals who were between 60 and 80 years of age. Study subjects completed food frequency questionnaires and were assigned a value on an antioxidant index scale, based on the volume and diversity of their antioxidant intake. Subsequently, subjects were placed in one of five quintiles according to the value of their antioxidant index. Those individuals in the fifth quintile (those with highest antioxidant indexes) were approximately 40 percent less likely to have wet AMD, an advanced form of the disease, than people in the first quintile (those with lowest antioxidant indexes). The antioxidant nutrients that comprised the study index were lutein, zeaxanthin, alpha carotene, beta carotene, beta cryptoxanthin, lycopene, vitamins C and E, zinc, and selenium.
Julie Rosenthal, MD, who presented results of the study at The Association for Research in Vision in Ophthalmology (ARVO) Annual Meeting in May 2006, said, “The message that we hope people will take home is that the study strengthens the evidence that a diet high in nutrients with antioxidant properties is associated with a decreased risk of having advanced AMD.”
Another study report, “Dietary Intake of Antioxidants and Risk of Age-Related Macular Degeneration,” was published in the Journal of the American Medical Association (December 28, 2005). In the report, investigators said that dietary antioxidant intake significantly reduced the risk of all forms of AMD. More than 4,000 people from Rotterdam, The Netherlands, aged 55 years or older, participated in this investigation. A food frequency questionnaire was used to evaluate study participants’ intake of a variety of antioxidants. The investigators concluded that “an above-median intake of the combination of vitamins C and E, beta carotene, and zinc was associated with a 35 percent lower risk of incident AMD.”
A number of other studies have evaluated antioxidants and AMD risk, though most have investigated antioxidant intake through supplementation. Some have compared blood levels of antioxidants with retinal health.
A stressful world for the fragile retina
The retina is a thin, delicate piece of tissue in the back of the eye that is comprised of a variety of different neuronal cells, including 125 million photoreceptors (rods and cones) that process light and enable you to see. Experts actually consider the retina to be an extension of the brain.
For many years, researchers have suspected that antioxidants might be beneficial to the health of the retina because it is subjected to so much oxidative and environmental stress; the retina processes a relatively large amount of oxygen and waste and is regularly bombarded by light. Furthermore, the antioxidants lutein and zeaxanthin are prevalent in the macula and are what give the center of the eye (behind the pupil) its dark pigment. Their role is thought to be protective.
The benefits of antioxidants in human health are not definitively understood—they can even be a topic of controversy. Still, many health experts believe that antioxidants are important in the diet because they protect the body’s cells and tissue from the damage that occurs as a result of normal, daily living and aging. Antioxidants also appear to protect our bodies from damage caused by ultraviolet light, X-rays, heat, cigarette smoke, alcohol, and pollutants.
More on AMD risk factors
Though dietary antioxidants may reduce your chances of developing AMD, there are a number of other factors that affect overall AMD risk.
Recently, researchers found a strong genetic link to the disease; as many as 74 percent of AMD cases may have a genetic connection. Genes that control your immune system and inflammatory responses appear to be involved. Experts have also known for many years that AMD runs in families.
Smokers are more likely to develop AMD than non-smokers. In fact, smoking is the most significant modifiable risk factor for AMD.
Though the effects of light exposure on the retina are not completely understood, most retinal experts agree that you should protect your eyes with sunglasses when outside in bright light. Use glasses that filter out both UVA and UVB rays.
Many health experts believe that, in general, an overall healthy lifestyle can reduce your risk of AMD; they say that what is good for your heart is also good for your retina.
See your ophthalmologist
Always visit an ophthalmologist if you notice changes in your vision. However, AMD can occur before noticeable changes. Only an ophthalmologist can diagnose the condition by conducting an exam of your retina.
The American Academy of Ophthalmology recommends that people between the ages of 40 and 64 visit an ophthalmologist every two to four years. People who are 65 and older should do so every one to two years.
Note: The AREDS formulation—an over-the-counter antioxidant supplement—is often prescribed to individuals who are at high risk of developing advanced AMD. The amounts of antioxidants in this formulation are higher than the amounts that can normally be obtained through diet. If your doctor has prescribed the AREDS formula for you, do not try to substitute fruit and vegetable consumption for the formulation. Always consult your physician if you have questions about your condition, diet, or supplementation.
Ben A. Shaberman is a writer and a frequent volunteer for VRG events throughout the Mid-Atlantic.