Research Brings New Hope for Nutritional Treatment of Age-Related Macular Degeneration

Research in recent years has shown that two nutrients--lutein and zeaxanthin--often used in nutritional supplements--work wonders in preventing age-related macular degeneration (AMD). When consumed, these nutrients reach the eyes from the gut--passing through the bloodstream--and play an important role in protecting the eyes against AMD. But it has been a mystery how these nutrients work. Unveiling this mystery, a recent research has come up with new hope for the Nutritional Treatment of AMD. The study, entitled Xanthophylls are preferentially taken up compared with β-carotene by retinal cells via a SRBI-dependent mechanism, has been published in the August 2008 issue of a professional journal, Journal of Lipid Research.

What the current study says…
The current study has been carried out by US researchers from the Ohio State University. Previous studies have shown that dietary compounds lutein and zeaxanthin can protect the eyes against age-related macular degeneration. These two compounds belong to a class of carotenoids called xanthophylls (carotenoids are organic pigments which absorb light; they’re divided into two classes: Xanthophylls and carotenes). Xanthophylls have the property to absorb blue light; they get accumulated in the macula area of retina and form a spot known as the fovea. This is why xanthophylls are also called macular pigments, and it’s believed that they have an important role in vision.
Although the main carotenoid that we obtain from diet is beta-carotene, its quantity in the retina is very small. About 80% of the carotenoid content in the retina is Lutein and zeaxanthin. The dietary sources for these nutrients are carrots, squash, peaches, papaya, broccoli, spinach, peas etc. Lutein and zeaxanthin, according to the current study, may have a definite mode of action through which they reduce the risk of AMD in elderly individuals.

In order to solve the mystery of how lutein and zeaxanthin protect the eyes against AMD, the researchers introduced these two nutrients, along with beta-carotene (for comparison), into the experimental cells of retina. The cells absorbed much more lutein and zeaxanthin compared to beta-carotene, the researchers noted. They also found that lutein and zeaxanthin did bind with a protein, called SR B1 (scavenger receptor class B, type 1), which acted as a transporter to carry those nutrients from the bloodstream to retina. The same protein was also involved during the absorption of lutein and zeaxanthin in the gut (by the cells in the intestine), the researchers found in an earlier work.

What’s different in this study?
It appears from this study that though beta-carotene is the major carotenoid we consume through diet, its importance in AMD is far less, compared to Xanthophylls, such as lutein and zeaxanthin. Lutein and zeaxanthin are the carotenoids, which substantially help reduce the risk of AMD, and thus nutritional treatment using these nutrients may yield impressive results, compared to nutritional treatment only with beta-carotene. That apart, further researches on the protein (i.e. SRB1)--which binds with lutein and zeaxanthin and acts as a transporter--may also yield a better transport means for lutein and zeaxanthin and thus leading to a better effectiveness of these nutrients in AMD.

How Lutein and zeaxanthin play their role in AMD…
Lutein and zeaxanthin are important constituents of the macula region of retina--they help form the fovea. So, it’s apparent that maintaining an increased concentration of these nutrients in the retina may protect the macula from degenerative changes. These nutrients also protect the eyes against AMD by working as antioxidants and thus reducing oxidative stress. That apart, these pigments also help protect the eyes against AMD by filtering blue light; blue light is known to be damaging for the macula.

AMD: a silent enemy…
AMD is a condition that affects a large number of elderly people worldwide, including nearly 10 million people in the United States. It affects the eyes slowly and silently, and gradually removes the power to see sharp and clear images of the objects around us, leading to difficulties in performing various important day-to-day activities, such as driving, reading, and doing finer work (for example, threading a needle). According to the National Eye Institute, AMD affects the macula, the center part of the retina (the light sensitive part at the back of the eyes) which is responsible for detailed vision. It’s a painless condition and a leading cause of vision loss in the US people aged 60 and more. The progress of AMD is very slow in some people, but in others it can progress rapidly, resulting in loss of vision in both eyes, according to the National Eye Institute. What is more concerning is that some forms of AMD have no cure. It can either be prevented, or medical measures can be taken up to control the progress of the disease. The symptoms of AMD are not specific, however, according to the University of Michigan Kellogg Eye Center, one may contact an eye doctor for a complete examination, if he or she experiences one or more symptoms such as: blurry vision, distorted vision, straight lines appearing wavy, wrong size and shape of objects, loss of clear and correct colors, difficulty in reading, and a dark and empty area in the center of vision. A regular eye check-up and carrying out necessary treatment under the supervision of an eye specialist is essential in tackling AMD in elderly individuals.

Nutritional Supplements: a boon in AMD, according to studies…
The role of nutritional treatment in AMD is well accepted by the medical community, thanks to the effectiveness of various nutritional supplements to prevent and control the disease. Given that AMD is the most common cause of blindness in elderly people in developed countries, and that various studies have shown that nutritional supplements can play a significant role in this disease, public interest is quite high regarding the nutritional treatment of AMD, which is why new research is taking place all over the world to explore how various nutrients can be used to tackle AMD. According to the National Eye Institute, AMD has two forms: Dry and Wet. The Dry form is more common, where Macula’s light sensitive cells slowly break down and central vision is lost gradually. But, in the Wet form, which is relatively less common (found in 10% of cases) but more dreaded, growth of abnormal blood vessels under the macula can be seen. The blood vessels, as explained by the National Eye Institute, often leaks fluid and blood under the macula and tend to cause it to elevate, resulting in rapid damage of the macula.

• In Dry AMD, supplementation with specific anti-oxidant vitamins and minerals is effective, according to the University of Michigan Kellogg Eye Center, because they can significantly slow down the progress of the disease. It’s believed that oxidative stress--with the aid of free radicals--contributes in the development of AMD. In  the retina, antioxidants work as free radical scavengers and thus fight against oxidative stress.
• In a study, a nutritional supplement comprising of vitamins A, C and E, omega 3 fatty acids, taurine, copper, zinc oxide, lutein and zeaxanthin, showed substantial improvement in the best-corrected visual acuity in 76.7% of the participants (number of participants was 37) with dry AMD after 6 months of nutritional treatment with these supplements. The study, entitled TOZAL Study: An open case control study of an oral antioxidant and omega-3 supplement for dry AMD, was published last year in the professional medical journal BMC Ophthalmology.
• Another study, entitled The Relationship of Dietary Carotenoid and Vitamin A, E, and C Intake With Age-Related Macular Degeneration in a Case-Control Study, which was published last year in the professional journal Archives of Ophthalmology, suggested that consuming lutein and zeaxanthin in higher amount can significantly reduce the risk of AMD.
• In the National Eye Institute’s Age-Related Eye Disease Study (AREDS), which included 4757 individuals, patients who consumed a nutritional supplement comprising of vitamins C and E, beta carotene and high-dose of zinc, had a 28% reduced rate of progression towards the “end-stage AMD” and it was also found that the supplement had a substantial effect in preventing the wet form of AMD.
• Another study, entitled Dietary Omega-3 Fatty Acid and Fish Intake in the Primary Prevention of Age-Related Macular Degeneration: A Systematic Review and Meta-analysis, which has been published in June 2008 in the Archives of Ophthalmology, suggested that consuming high amount of omega 3 fatty acid in the diet can significantly reduce the risk of late AMD. The risk of both early and late AMD was found lower in individuals who consumed fish at least twice a week. Fish such as herring, tuna, salmon, sardines, mackerel etc, are the rich source of Omega 3 fatty acids, however, it can also be found from plant sources such as Soybean oils, walnuts and canola. 
• Having a substantially high blood level of vitamin D can significantly reduce the risk of AMD, suggests a study that looked at data obtained from 7,752 individuals who were included in the third National Health and nutrition examination survey between 1988 and 1994. The study, entitled Association Between Vitamin D and Age-Related Macular Degeneration in the Third National Health and Nutrition Examination Survey, 1988 Through 1994, was published last year in the Archives of Ophthalmology. According to the study, vitamin D level in the blood was inversely associated with the risk of early AMD, and vitamin D might have a protective role against the disease. The researchers also looked at consumption of milk and fish, two dietary sources of vitamin D, and found that milk intake was inversely linked with early AMD and fish intake was inversely associated with advanced AMD.

Paul Krawitz, M.D., President
Vitamin Science Inc