October 2013 Issue

Age-Related Macular Degeneration
By Megan Tempest, RD
Today’s Dietitian
Vol. 15 No. 10 P. 50

Learn about the role certain foods and nutrients play in preventing and slowing the progression of this sight-threatening disease.

By the time Bob celebrated his 75th birthday, he was having trouble recognizing the faces of his neighbors—people he’d known for more than 20 years. Simple tasks such as reading food labels, doing crossword puzzles, and reading his favorite magazines now were a challenge. Bob was experiencing the life-altering effects of age-related macular degeneration (AMD), one of the leading causes of blindness among older adults in the United States.

The Centers for Disease Control and Prevention estimates that AMD affects approximately 1.8 million Americans aged 40 and older, and an additional 7.3 million are estimated to be at risk of developing the disease. Moreover, it’s projected that the number of Americans with AMD will reach nearly 3 million by the year 2020.1

Following is a discussion on AMD and the foods and nutrients that research shows may prevent and slow its progression.

What Is AMD?
AMD is a disease that gradually destroys the macula, a small region in the center of the retina—a light-sensitive layer of tissue that lines the inner surface of the back of the eye—that contains millions of light-sensing cells known as photoreceptors responsible for clear central vision. AMD usually doesn’t affect peripheral vision.2

“What is significantly impacted by macular degeneration is facial recognition and reading. Those are the big complaints we hear from people with the disease,” says Jennifer Kaldenberg, MSA, OTR/L, SCLV, FAOTA, an occupational therapist and clinical assistant professor at Boston University Sargent College of Health & Rehabilitation Sciences and an adjunct faculty member at the New England College of Optometry & New England Eye Institute, who specializes in working with adults with vision impairment.

To simulate the central blindness caused by advanced AMD, Kaldenburg suggests placing your fist at the bridge of your nose, so that everywhere you look you’re viewing a blind area. “Getting around, walking, and being safe in your mobility generally isn’t an issue with AMD,” she says, “but activities that require reading or seeing people’s faces are difficult. For instance, if someone is being sarcastic with their facial expressions, nodding their head, or making other facial gestures, the person with AMD may not see them. That person may become socially isolated because they miss those social cues and therefore feel uncomfortable in social situations.”

There are two different forms of AMD: dry and wet. Dry AMD is divided into three stages: early, intermediate, and advanced. Dry AMD is the more common form, affecting approximately 90% of those with the disease. It’s characterized by its slow degeneration of the macula and therefore its slow progression to vision loss, preventing many individuals from experiencing significant symptoms. However, for a smaller percentage of people, dry and wet AMD does progress to an advanced stage. The wet form almost always leads to severe vision loss because it causes swelling and rapid damage to the macula and possibly scarring of the retina. Wet AMD always starts as dry AMD. In fact, dry AMD can transition to wet AMD at any time without notice.2

The vision loss AMD causes is irreversible, but if it’s detected early by a comprehensive dilated eye exam, patients can begin retinal treatments to slow the progression of the disease.2

AMD Risk Factors
According to the National Eye Institute, AMD risk factors include the following2:

Age: Adults aged 50 and older are at increased risk of AMD, and that risk continues to rise with age.

Genetics: Patients with a family history of AMD are believed to have an increased risk of developing the disease.

Smoking: People who smoke are said to be twice as likely to develop AMD as nonsmokers.

Race: Whites are significantly more likely to develop AMD than people of African descent.

Nutrition and AMD
A discussion about AMD and nutrition can’t begin without first addressing the Age-Related Eye Disease Study (AREDS), a large, randomized clinical trial that was conducted by the National Institutes of Health’s National Eye Institute. Initiated in the early 1990s, this landmark study provided strong evidence that consuming high doses of certain nutrients can help prevent or slow the progression of AMD.3

When researchers gave patients a formulation of high-dose antioxidants plus zinc, they observed a 25% reduced risk of developing more advanced AMD and a 19% lower risk of central vision loss among individuals with intermediate or advanced disease. The formulation didn’t appear to slow AMD progression among those in the early disease stage. The nutrient formulation contained vitamin C (500 mg), vitamin E (400 IU), and beta-carotene (15 mg) plus zinc (80 mg). Two milligrams of copper were added to prevent copper deficiency that’s associated with high levels of zinc supplementation.4

These findings established the first demonstrated AMD treatment that medical professionals could recommend to patients with diagnosed intermediate to advanced disease in hopes of slowing its progression.4 What followed was the introduction of several brand-name supplements to the public containing roughly the same antioxidant formulation used in the AREDS study.

AREDS2 Study
In May, the National Eye Institute completed a follow-up study called the Age-Related Eye Disease Study 2 (AREDS2), which clarified the role of supplements in helping prevent advanced AMD.5

Initiated in 2006, the study tested whether the original AREDS formulation could be improved by adding omega-3 fatty acids (1,000 mg), lutein (10 mg), and zeaxanthin (2 mg) along with removing beta-carotene or reducing zinc. The study also evaluated how different combinations of the supplements impacted AMD progression. Ultimately, beta-carotene was removed because of its association with an increased lung cancer risk among smokers and former smokers.6

The researchers found that omega-3s didn’t provide any additional benefit to AMD patients. Subjects with a low dietary intake of lutein and zeaxanthin—found in foods such as corn, eggs, and green, leafy vegetables—at the beginning of the study but who took the AREDS formulation containing these two antioxidants were approximately 25% less likely to develop advanced AMD. In addition, lutein and zeaxanthin were considered a safe and effective alternative to beta-carotene, one that wouldn’t pose a health risk to smokers.6

The findings from both AREDS studies, as well as subsequent research that upholds these findings and suggests there are no apparent side effects from long-term supplementation, have convinced eye health professionals to recommend an AREDS-type supplement to patients at risk of developing advanced AMD.7,8 “The retina community feels strongly that the beneficial affects of the nutrients are real and worth putting people on the supplements,” says Marc Levin, MD, a board-certified retina specialist and clinical assistant professor at the University of Illinois College of Medicine.

Levin says he often recommends supplements to patients who have been diagnosed with intermediate and advanced AMD. “There are a few outliers but doing so is a generally accepted, almost universal practice.”

Omega-3s and AMD Prevention
Although omega-3s didn’t show a benefit to AMD patients in the AREDS2 study, several studies suggest that omega-3s promote eye health and may help prevent AMD. The Blue Mountain Eye Study suggested that regular consumption of fish containing omega-3 polyunsaturated fatty acids as well as nuts was associated with a lower risk of early AMD development.9

A study published in the July 2011 issue of Archives of Ophthalmology analyzed a large cohort of females without an AMD diagnosis at baseline and found that regular DHA and EPA consumption as well as fish was associated with a significantly decreased risk of developing AMD.10

Findings from the Rotterdam study, published in the June 2011 issue of Archives of Ophthalmology, showed that high dietary intakes of omega-3 fatty acids (as well as antioxidants and zinc) may reduce the risk of early AMD in individuals with a high genetic risk and stated that “clinicians should provide dietary advice to young susceptible individuals to postpone or prevent the vision disabling consequences of AMD.”11

Moreover, a study published in March in JAMA Ophthalmology evaluated the effectiveness of high-dose oral omega-3 fatty acid supplementation (4 g/day for six months) in patients with dry AMD. The researchers found that this high dose could effectively raise a person’s serum omega-3 index although, in the short term, supplementation didn’t invoke significant changes in visual acuity or retinal function among subjects.12

The Dietitian’s Role
Given the relationship among healthful foods, certain nutrients, and AMD development, nutrition professionals can educate clients and patients who are either at risk of or already have been diagnosed with the disease.

Ruth Frechman, MA, RD, CPT, a spokesperson for the Academy of Nutrition and Dietetics, believes dietitians should have greater awareness of their role in AMD prevention, since the typical diet of many Americans is low in nutrients and antioxidants such as lutein and zeaxanthin, which are important to eye health. “If we get enough of these nutrients through food, or even supplements, our blood levels do go up and therefore can protect the eye from damage,” she says.

From this standpoint, Frechman recommends the regular consumption of eggs, corn, and green, leafy vegetables such as kale, spinach, cooked turnip greens, or collards. “Everyone is smoothie crazy these days, “ she adds, “throwing anything and everything [into their smoothies], like kale and spinach. This is good news because these leafy greens are great sources of lutein and zeaxanthin.”

Levin supports the dietitian’s role in helping people prevent the potentially devastating effects of AMD. He believes AMD sufferers shouldn’t rely on supplements alone. “Even though these [AREDS] supplements have been shown to have some value, we still need nutrients from whole food,” he says. “We don’t want people on a poor diet thinking that taking these supplements is going to keep them in a good state of health. We don’t know what else, besides the specific nutrients and antioxidants, is in whole foods that may be contributing to the beneficial affects on macular degeneration.”

The following three strategies can help dietitians prevent AMD in clients and patients:

1. Identify individuals at increased risk of developing AMD by using questionnaires to determine who may have AMD risk factors, including those listed previously.

2. Discuss dietary habits and lifestyle behaviors that may help prevent AMD. As mentioned, encourage clients to eat foods rich in vitamin C, omega-3 fatty acids, lutein, and zeaxanthin, which have been shown to support eye health (see below). 

3. Refer at-risk patients to an eye health professional. When AMD is detected early, nutritional supplementation can help prevent AMD development or delay its progression.

Moving Forward
AMD may be irreversible, but it can be prevented. Kaldenburg says that older adults shouldn’t accept vision loss as a normal part of aging: “Unfortunately, a lot of people associate visual decline as a normative aging change. Macular degeneration is a disease process; it’s not normative aging.”

Knowing about AMD risk factors, adopting a diet rich in nutrients that support eye health, and practicing healthful lifestyle behaviors all enable a person to avoid the potentially devastating affects of AMD. Dietitians can be instrumental in giving that power to their clients and patients.

Looking ahead, additional research hopefully will further clarify how food and nutrients can serve in primary prevention of this leading cause of blindness.

— Megan Tempest, RD, is a dietitian at Boulder Community Hospital in Colorado and a freelance writer.

 

Key Nutrients for Eye Health13

Lutein and Zeaxanthin
These two nutrients are found in high concentrations in the macula, a small region in the center of the retina—a light-sensitive layer of tissue that lines the inner surface of the back of the eye—that contains millions of light-sensing cells known as photoreceptors responsible for clear central vision. Lutein and zeaxanthin act as antioxidants, protecting the eye from environmental damage caused by smoking, pollutants, and sun exposure.

Food sources: Dark, leafy, green vegetables such as spinach, kale, and collard greens. It’s found in lesser amounts in broccoli, Brussels sprouts, corn, romaine lettuce, peas, and eggs.

Omega-3 Fatty Acids
These polyunsaturated fatty acids support eye health by preventing arterial plaque buildup and also reducing inflammation and blood vessel and cell damage.

Food sources: Cold-water fish high in both DHA and EPA, such as wild salmon, herring, sardines, tuna, or cod liver oil. Plant-derived omega-3 fats are found in flaxseeds, walnuts, and dark green, leafy vegetables.

Zinc
Zinc plays a role in bringing vitamin A from the liver to the retina to produce melanin, the protective pigment in the eyes. Zinc is concentrated in the retina as well as the vascular tissue layer underneath the retina.

Food sources: Red meat, seafood, poultry, pork, oysters, eggs, nuts, tofu, baked beans, wheat germ.

Vitamin C
Vitamin C is actively concentrated in eye tissue and supports the health of ocular blood vessels.

Food sources: Citrus fruits, including oranges, lemons, limes, and grapefruits, as well as red peppers, tomatoes, and spinach.

Vitamin E
Vitamin E is an antioxidant for the eye, protecting it from environmental damage and free radicals that harm healthy eye tissue. It plays a role in vital biological processes, such as DNA repair, and maintains healthy cell membranes.

Food sources: Nuts, such as almonds and peanuts, as well as sunflower seeds, vegetable oils, wheat germ, fortified cereals, and sweet potatoes.

— MT

 

References
1. Common eye disorders: age-related macular degeneration. Center for Disease Control and Prevention website. http://www.cdc.gov/visionhealth/basic_information/eye_disorders.htm - a3. Last updated April 23, 2013. Accessed July 31, 2013.

2. National Eye Institute. Age-Related Macular Degeneration: What You Should Know. Washington, DC: US Department of Health and Human Services; 2009. NIH Publication No. 09-2294.

3. Age-related eye diseases study—results. National Eye Institute website. http://www.nei.nih.gov/amd/background.asp. Accessed July 31, 2013.

4. Antioxidant vitamins and zinc reduce risk of vision loss from age-related macular degeneration. National Eye Institute website. http://www.nei.nih.gov/news/pressreleases/101201.asp. October 12, 2001. Accessed July 31, 2013.

5. NIH study provides clarity on supplements for protection against blinding eye disease. National Eye Institute website. http://www.nei.nih.gov/news/pressreleases/050513.asp. May 5, 2013. Accessed August 2, 2013.

6. Question and answers about AREDS2. National Eye Institute website. http://www.nei.nih.gov/areds2/MediaQandA.asp. Last updated May 2013. Accessed August 2, 2013.

7. Chew EY, Clemons TE, Agrón E, et al. Long-term effects of vitamins C and E, β-carotene, and zinc on age-related macular degeneration: AREDS report No. 35. Ophthalmology. 2013;120(8):1604-1611.

8. Sin HP, Liu DT, Lam DS. Lifestyle modification, nutritional and vitamins supplements for age-related macular degeneration. Acta Opthalmol. 2013;91(1):6-11.

9. Tan JS, Wang JJ, Flood V, Mitchell P. Dietary fatty acids and the 10-year incidence of age-related macular degeneration: the Blue Mountains Eye Study. Arch Ophthalmol. 2009;127(5):656-665.

10. Christen WG, Schaumberg DA, Glynn RJ, Buring JE. Dietary ω-3 fatty acid and fish intake and incident age-related macular degeneration in women. Arch Ophthalmol. 2011;129(7):921-929.

11. Ho L, van Leeuwen R, Witteman JC, et al. Reducing the genetic risk of age-related macular degeneration with dietary antioxidants, zinc, and ω-3 fatty acids: the Rotterdam study. Arch Ophthalmol. 2011;129(6):758-766.

12. Gerstenblith AT, Baskin DE, Shah CP, et al. Electroretinographic effects of omega-3 fatty acid supplementation on dry age-related macular degeneration. JAMA Ophthalmol. 2013;131(3):365-369.

13. Nutrition and AMD. American Optometric Association website. http://www.aoa.org/patients-and-public/eye-and-vision-problems/glossary-of-eye-and-vision-conditions/macular-degeneration/nutrition-and-amd. Accessed August 2, 2013.

 

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