Natural Products Insider

NOV-DEC 2016

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Page 34 of 74

I began doing research on the macular carotenoids, lutein (L) and zeaxanthin (Z), in the late 80s. At that time, there was very little interest in the macular pigments (MP). Our fi rst study was a simple comparison showing that the amount of LZ in the left and right eye was, essentially, the same. 1 Although a straightforward study, delivering equal amounts of L and Z to each eye is not so simple. L and Z are ingested, absorbed through the gut, packaged with lipoproteins in the liver, cross the retina-blood barrier, attach to binding proteins, etc.: the fact that all of this could be done in precisely the same manner for both eyes suggested a biology that was tightly controlled. Since L and Z are pigments, like melanin in the iris, one early interpretation was that genetics might play an important role in this process. Our next study, consequens est, was measuring identical twins. 2 In that study we found that identical twins often had very different levels of MP and that those differences were relatable to similar differences in their diet. This led to the idea that MP could be increased by supplementation or dietary change and this was confi rmed empirically. 3 In the process of measuring MP in all of these different people it was hard not to notice just how different individuals could be: some had very high MP levels, some had very low. There was a growing literature showing that such variation appeared to impact a host of degenerative diseases. This made sense since so many of these late-stage conditions, ranging from cardiovascular to ocular disease, were linked to oxidative and infl ammatory stress. The idea was that L and Z, by preventing oxidative and infl ammatory stress, would lower risk over time. Were they actually there, however, to prevent degenerative disease? Biology is largely determined by natural selection and it was hard to see how preventing diseases one gets later in life (past reproductive ages) would be a suffi cient selective pressure. Rather, it seemed likely that L was infl uencing some aspect of daily function that would manifest early. Since L concentrates so strongly in the macula (the highest concentration of carotenoids in the body), and strongly absorbs a full third of the visible spectrum (with a peak corresponding to the blue of sky light), visual function seemed like a good place to start looking. Although visual function is often thought of relatively simplistically (like seeing the big E on a Snellen acuity chart), it is actually one of the most complex tasks our central nervous system performs. The visual image itself is enormously complex containing elements that are often moving, at different depths, colors, and spatial frequencies with shifting illuminance. These stimulus energies enter the eye and then are transformed neurologically into symbols that bear only a passing relation to the original event (e.g., wavelength gives rise to the contrived perception, color). How might L and Z infl uence this vast process requiring complex optics and millions of neurons? In the eye, L and Z are concentrated in the inner layers forming a dense yellow fi lter between incoming light and the photoreceptors. Given this fi ltering function, we felt a good place to start would be testing vision under bright light circumstances. 4 To ensure ecological validity, we carefully mimicked natural sunlight (still, a major source of photostress and glare disability and discomfort). In a long series of studies, by ourselves and others, we found that LZ levels within the retina strongly predicted an individual's ability to see under intense light circumstances. Further, we found that supplements, which increase retinal LZ, directly reduce glare disability and shorten recovery times when exposed to blinding fl ashes of light (photostress recovery). 5 Nor, were we soon to discover, the effects limited to bright light conditions. We also found that the pigments improve chromatic contrast and visual range: both measures that dramatically infl uence how well and how far one can see outdoors. 6 All of this work showed quite directly that the macular pigments improve the optics of the eye in a way that improves visual function in ecological settings. Lutein, however, like vision itself, is something that is not found in the eye alone. Optical images are processed into meaningful percepts by the brain. Recent research has found that lutein is also found within brain regions responsible for this processing suggesting that the pigments could also infl uence, not just the optics of an image, but the neural processing of that image as well. 7 Our latest research has found that the macular pigments are related to visual processing speed (mediated by the visual cortex) and the ultimate result of that processing, cognition itself. 8,9 Taken together, lutein in particular, appears to have special signifi cance, not just for overall health but for everyday functions such as improved visual optics, balance ability, information processing, memory, etc. E.A. Bucchianeri was once quoted as saying "If you are what you eat, you are what you seeā€¦" Perhaps we should not be surprised at how bidirectional such observations turned out to be. Dr. Hammond is a full Professor in the Brain and Behavioral Sciences program at the University of Georgia (UGA). He is also faculty in the Foods and Nutrition and Gerontology program at UGA and the Director of Graduate Studies. His bachelors in Science was obtained at the University of Oregon and his Ph.D. was received at the University of New Hampshire. He was a postdoctoral fellow at Harvard Medical School and a professor for several years at Arizona State University before coming to UGA in 1999. He has published over 100 empirical papers and numerous chapters, reviews, and theoretical papers on the biology of the visual system (e.g., retinal carotenoids) and brain. One major focus of this work is understanding the role of behavior, especially dietary, in neural development and disease. ADVERTORIAL Macular Pigment & Visual Function References available upon request at fl Certain statements may not be applicable in all geographical regions. Labeling and claims may differ based upon government requirements.

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