April 2010

 

OPHTHALMOLOGY NEWS

 

Carotenoid contenders to improve visual function


by Maxine Lipner Senior EyeWorld Contributing Editor 

   

Dietary pigments, lutein and zeaxanthin, can help to screen out glare

Billy R. Hammond Jr., Ph.D.

Carotenoids lutein and zeaxanthin can help to stave off glare and quicken the time a person’s eyes can recover after being exposed to blinding flashes, such as those from oncoming headlights, according to Billy R. Hammond Jr., Ph.D., professor of neuroscience and experimental psychology, University of Georgia, Athens, Ga. In the December 2009 issue of the Journal of Food Science investigators reported that visual performance in normal eyes can be affected by macular pigments such as lutein and zeaxanthin.

Considering the role that these two nutrients could play in visual performance seemed to be natural to investigators. “Carotenoids are very widespread in nature—humans absorb about 20 or so in the blood,” Dr. Hammond said. “But lutein and zeaxanthin are the only two carotenoids that actually go into the eye.” As a result, these two nutrients have garnered attention in this area before. “Vision researchers have thought for a long time that they play a special role in vision,” Dr. Hammond said. “In fact, they’re all throughout the eye and concentrated in the visual areas of the brain as well.” These two carotenoids play a role in how fast the brain processes information. “A lot of the information that we process comes through the visual system,” Dr. Hammond said. “They have a pretty widespread role in visual function.”

Foods high in lutein and zeaxanthin tend to be marked by a bitter taste and a green color. “It’s the dark green leafies that have lutein and zeaxanthin,” Dr. Hammond said. “Eggs are also a good source; the yellow yolk has carotenoids.” Since these two nutrients are fat soluble they need some fat in order to be absorbed properly. “Eggs become a very good matrix for absorbing these pigments,” Dr. Hammond said.

A compilation study

Investigators compiled studies from the literature to look at the role these nutrients potentially play in a variety of types of visual function. One of the real-life situations considered was that of driving at night and encountering bright headlights. Investigators questioned whether having a storehouse of such nutrients might help to stave off the disability from encountering those. “People vary pretty dramatically in how much of these pigments they have,” Dr. Hammond said. “You can find individuals with virtually none and others who have very high amounts.” Dr. Hammond once did a dietary analysis of the University of Georgia’s undergraduates. “You could get as much carotenoids as they have in a cup of spinach a week because they have such poor diets,” he said. “The national average is about one to two milligrams a day, and that’s pretty low.”

How would individuals with such low levels of these potent antioxidants differ from those with diets rich in these? When investigators in this study delved into the literature they found a definite protective effect. “The key results were that increases in the amount of these carotenoids in the retina were directly related to improved glare disability and photo-stress recovery,” Dr. Hammond said. “These yellow pigments are a filter; they’re in the layers of the retina and that’s how they reduce glare problems.” One new aspect of the research is that it centered on healthy eyes and everyday vision. “Most of the research on this topic in our lab and in others in the past has focused on how these pigments prevent eye disease,” Dr. Hammond said. “The key with nutrition and eye disease is that it takes an entire lifetime to develop.” As a result, Dr. Hammond sees this as a different kind of study. “This is certainly new in the sense that it isn’t about disease,” he said. “It’s about how this could improve vision, and that’s really for everyone.”

Definitive take-home message

In Dr. Hammond’s view the take-home message is clear cut. “People need to eat more green leafy vegetables,” he said. In more of a gray zone is the question of whether or not to use lutein and zeaxanthin supplements. For those who have an extremely good diet this may not be necessary. “If you’re a Paleolithic hunter and you eat mostly green leafy vegetables that are collected out of the field you wouldn’t need to, but it’s hard to do that nowadays,” Dr. Hammond said. “The quality of the food supply is not wonderful, frankly.” He recommends that most people use at least some supplements. “If I were to supplement I would do it two or three times a week, maybe when I had a fatty meal,” he said.

Looking to the future, Dr. Hammond thinks that carotenoids are going to play an important role in other ocular areas such as in the maturation of the visual system in babies. In addition, he sees these as becoming important in relation to cognitive function. “The retina is neural tissue and reflects neural tissue in other parts of the body like the brain,” he said. “The big co-morbidity there is Alzheimer’s disease.” The thinking is that something that prevents degeneration of the retina will do the same for the brain. “It turns out that this seems to do that,” Dr. Hammond said. “Supplementing lutein also appears to improve cognitive function quite substantially.”

Editors’ note: Dr. Hammond received funding from DSM Nutritional Products (Basel, Switzerland).

Contact information

Hammond: bhammond@uga.edu

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