IMPROVED NUTRITION MAY REDUCE THE RISK OF MACULAR DEGENERATION
George Torrey, Ph.D.
“The traditional thinking is that as age increases, visual sensitivity decreases. But what we are saying is, maybe that's not inevitable,” said D. Max Snodderly, Ph.D., head of the laboratory at The Schepens Eye Research Institute in Boston, Massachusetts, an affiliate of Harvard Medical School. “Improved nutrition could help to retard the loss of visual sensitivity with age. Perhaps the gradual loss of vision in many older people is not an inevitable consequence of the aging process. ” Dr. Snodderly, with co-authors Billy Hammond and Billy R. Wooten, reported their findings in Investigative Ophthalmology & Visual Science.(1.)
Increasing macular pigment density may slow, or possibly even reverse, the progression of age-related macular degeneration.
Consumption of fruits and vegetables containing two carotenoid pigments may be linked to a reduced risk for age-related macular degeneration, the leading cause of vision loss in people over the age of 55. According to research, lutein and zeaxanthin comprise a component of the central region of the retina and may play a role in some aspects of visual acuity. Increasing the concentration of these pigments in the eye may prevent the devastating vision loss caused by age-related macular degeneration.
Carotenoids are phytochemicals (chemicals found in plants) commonly found in certain fruits and vegetables that provide the red, orange and yellow colors of these foods. Lutein and zeaxanthin are found primarly in broccoli, corn, squash and dark green leafy vegetables like spinach and kale.
Lutein and zeaxanthin are concentrated in the fovea, the central region of the retina, in a spot known as the macula lutea, or yellow spot. The macula helps produce the sharp central vision needed for activities like reading, sewing and driving.
“The highest accumulation of lutein and zeaxanthin in the body is in the eye, ” said John Landrum, Ph.D., a leading researcher of the macular pigments of the eye. “Because of their high concentration in the eye and their high concentration at the point of greatest visual acuity, we believe they play an important role in the health of the macula.”
“When we compared the amount of macular pigment, which is comprised of lutein and zeaxanthin, present in the eyes of people with age-related macular degeneration to people without the disease, those with the lowest levels of carotenoid accumulation in the outer retina were significantly more likely to suffer from age-related macular degeneration than those with higher pigment levels, ” said Dr. Landrum. “The difference in risk between those having the highest and lowest levels was 75 percent.”
For the vast majority of those with age-related macular degeneration (AMD), there is no known cure or treatment. Symptoms of AMD include blurred or fuzzy vision; the illusion that straight lines, such as sentences on a page, are wavy; and the appearance of a dark or empty area in the center of vision. Risk factors for the disease include cigarette smoking and family history of AMD. Exposure to sunlight, having light irises, and even being a woman appear to be additional risk factors.
Researchers theorize that lutein and zeaxanthin protect the macular pigment in two ways: by absorbing harmful blue light from the sun's rays and by acting as antioxidants that neutralize free radicals. Free radicals are harmful molecules that are produced through normal body processes, such as oxygen metabolism. Environmental sources of free radicals include cigarette smoke, air pollutants, radiation, certain drugs and environmental toxins.
Further evidence linking lutein and zeaxanthin to the maintenance of eye health was provided with data from two Harvard studies - the Physicians' and Nurses’ Health Studies. Both reports demonstrate an inverse relationship between dietary intake of lutein and zeaxanthin from fruits and vegetables and the development of cataracts severe enough to require surgery.
Most Americans do not consume enough lutein- and zeaxanthin-rich fruits and vegetables to get the protection they need. According to Linda Nebeling, Ph.D., R.D., of the National Cancer Institute, national data shows an overall decline in lutein intake, particularly in groups at greatest risk for age-related macular degeneration. Between the years 1987 and 1992, lutein intake declined by 16 percent in women of all ages and in men and women aged 40 to 69.
“Women in the United States have decreased their consumption of vegetables like corn, green beans, broccoli, spinach, carrots and winter squash, ” said Dr. Nebeling. “These vegetables are rich sources of carotenoids and other important nutrients. Consuming too little of these foods could lead to an increased risk of disease.”
According to an article in The British Journal of Ophthalmology(2.) eating green leafy vegetables, which are rich in lutein and zeaxanthin, may decrease the risk for age-related macular degeneration. The goal of this study was to analyze various fruits and vegetables to establish which ones contain lutein and/or zeaxanthin and can serve as possible dietary supplements for these carotenoids.
Egg yolk and yellow corn contain the highest mole percentage (% of total) of lutein and zeaxanthin (more than 85% of the total carotenoids). Yellow corn was the vegetable with the highest quantity of lutein (60% of total) and orange pepper was the vegetable with the highest amount of zeaxanthin (37% of total). Substantial amounts of lutein and zeaxanthin (30-50%) were also present in kiwi fruit, grapes, spinach, orange juice, zucchini, and different kinds of squash. The results show that there are fruits and vegetables of various colors with a relatively high content of lutein and zeaxanthin.
Most of the dark green leafy vegetables, previously recommended for a higher intake of lutein and zeaxanthin, have a 15-47% of lutein, but a very low content (0-3%) of zeaxanthin. This study shows that fruits and vegetables of various colors can be consumed to increase dietary intake of lutein and zeaxanthin.
Dr. Johanna M. Seddon and her associates at Harvard University(3.) found that 6 mg per day of lutein lead to a 43 percent lower risk for macular degeneration. Half a cup of cooked kale contains 10.3 mg of lutein while one-half a cup of cooked spinach provides 6.3 mg.
The Schepens Eye Research Institute 1998 study concluded that vision loss associated with aging maybe preventable - even reversible - through improved nutrition. Although visual sensitivity decreases with age, this process need not be inevitable.
In that study, D. Max Snodderly, Ph.D., head of the laboratory at The Schepens, concluded that dietary factors associated with macular pigment appear to protect the retina from loss of sensitivity. Dark green and orange plants and fruits, like spinach, broccoli, green beans, corn and peaches, are especially effective.
In The Schepens study, older subjects with high macular pigment density retained their youthful visual function. Increasing macular pigment density may slow, or possibly even reverse, the progression of the disease. Thus one can understand the importance of pursuing the right nutritional program.
The Schepens study further concludes that in the future it may be possible to tailor dietary recommendations to an individual. Dr. Snodderly added that “These results are consistent with public health recommendations for prevention of chronic diseases such as heart disease and cancer. They indicate that what is good for the rest of the body is good for the eyes as well.”
For more information and to see a table listing foods rich in lutein, click here
For more information and to see a table listing foods rich in zeaxanthin, click here
George Torrey, Ph.D., a graduate of Brown (‘61), Harvard (‘62) and the Univ. of Connecticut (‘68), writes for the AMDF Newsletter and the AMDF Web site. Both his parents suffered from macular degeneration.
1. Investigative Ophthalmology & Visual Science (Feb. 1998, Vol. 39, No. 2)
2. The British Journal of Ophthalmology (Aug. 1998, 82: 907-910)
3. Journal of American Medical Association (1994, 272: 1413-20)