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 beta-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
Age-related Macular Degeneration affects nearly 10 millions 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 a detailed vision. It's a painless condition and a leading cause of vision loss in the US people aged 60 and more.
Nutritional Supplements: a boon in AMD
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 the nutritional treatment to tackle AMD. However, here is what some previous studies say regarding effectiveness of nutritional supplements in AMD:
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 with dry AMD after 6 months of nutritional treatment with these supplements. The study was published last year in the professional journal BMC Ophthalmology .
Another study 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 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".
Another study 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.
High level of vitamin D in blood significantly reduces the risk of AMD, suggests a study published last year in Archives of Ophthalmology . According to the study, vitamin D level in blood was inversely associated with the risk of early AMD.
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