Nutrition conference speakers stress importance of carotenoids
Presenters at the Brain and Ocular Nutrition Conference said nearly all components of visual performance are enhanced through increased carotenoid intake.
The importance of macular pigment was a common theme at the Brain and Ocular Nutrition Conference, formerly the Macular Carotenoid Conference, held in Cambridge, England.
Increasing one’s macular pigment is correlated with increased vision and performance. A lack of or declining level of carotenoids correlates with both cognitive decline and chronic diseases such as age-related macular degeneration, dementia and Alzheimer’s.
Conference chair John Nolan, PhD, explained that the change of the conference name reflected recent research developments that demonstrate how carotenoids are not just beneficial for visual performance and eye health, but also for brain health.
The conference focused primarily on the carotenoids found in the human eye and brain — lutein, zeaxanthin and mesozeaxanthin — and was divided carotenoid research in child development, vision performance and protection, and dementia and Alzheimer’s disease. Twenty-three speakers described their research during the 3-day meeting, and the topics ranged from genetically engineering food sources to the importance of lifelong intake of the key carotenoids for improving both visual and brain function. Additionally, 34 posters were presented on carotenoid research concepts in development.
The Brain and Ocular Nutrition Conference’s first day highlighted how macular carotenoids affect visual performance and contrast sensitivity. It also highlighted the bioavailability and transport of carotenoids as well as healthy brain aging.
Duke Eye Center’s Visual Performance Laboratory research scientist, James M. Stringham, PhD, started off the conference discussing the importance of macular carotenoids to visual performance.
He explained that visual performance encompasses temporal processing speed, reaction time, prediction and decision making. Owsley and Sloane found visual performance to be a much better predictor of how a person performs in the real world versus simply assessing their age or visual acuity.
Visual performance is strongly impacted by contrast sensitivity, glare and dark adaptation, Stringham said. The ability to react to changes in light levels, even when adjusting for age, varies greatly from person to person. Glare and contrast sensitivity are affected by both external and internal variables, with internal referring to inner-eye changes over time, such as cataracts. While many variables can negatively impact visual performance, increasing carotenoids in the eye and brain improve nearly every component, Stringham said.
Macular pigment assists the retina in several fundamental ways, he said. It promotes healthy tissue by lowering oxidative stress and reducing inflammation; it filters blue light, resulting in decreased glare, and increases chromatic contrast enhancement; and it has neurophysiological effects on contrast sensitivity, visual cycle kinetics and visual processing speed. In fact, for every 0.1 log unit increase in macular pigment, temporal processing speed may increase by as much as 1 millisecond.
Macular pigment optical density is measured in log units ranging from 0 to 1.65, with every 0.3 log unit doubling the concentration of pigment (0.5 log units to 0.8 log units would be a doubling, as would 0.8 log units to 1.1 log units). An improvement from low to high macular pigment optical density can increase processing speed by as much as 10 milliseconds, which is significant (think professional athletes, video gamers, etc.).
Mark Roark, OD, who practices in Indiana, presented information from his clinical research on contrast sensitivity threshold (CST) in patients taking carotenoid supplements. He measured CST with the Macular Densitometer (developed by Billy R. Wooten, PhD, from Brown University) by using a rapid assessment, which can be easily performed using a variation of the Pelli-Robson chart on an LCD screen, he said.
This rapid assessment, the Harris Contrast Test, utilizes Sloan letters to measure CST and is documented for each eye by cycles per degree (cpd) at a percentage (for example: OD at 6 cpd 2.5%). Research shows that when no ocular pathology is present, the expected CST will most often measure an average of 2.0% to 2.5% photopic CST utilizing a 20/100 letter (Owsley and Sloan).
Roark presented a comparison of how improvement in contrast sensitivity correlates with an improvement in Snellen visual acuity: Improving two lines of Snellen visual acuity, from 20/32 to 20/20, would be the same as increasing CST from 2.5% to 1.6% (normal for young subjects ranges between 1.5% and 2.5%, and after 60 years of age, normal ranges between 2.5% and 3.2%).
Torsten Bohn, PhD, principal investigator and project leader for the Luxembourg Institute of Health, stated that bioavailability may vary profoundly based upon dietary factors, dietary lipids and divalent minerals. Host factors, such as intestinal diseases (eg, Crohn’s) can affect how nutrients are absorbed. Other lifestyle factors may also play a role, such as obesity, alcohol consumption and smoking. And there may be inherent genetic differences that alter digestion, transport, metabolism and tissue uptake of dietary consumed carotenoids.
Whenever a tissue exhibits highly selective uptake of a compound, it is likely that one or more specific binding proteins are involved in the process, Bohn said. Li and colleagues found carotenoid-binding proteins from the human retina including a Pi isoform of glutathione S-transferase (GSTP1) as a zeaxanthin-binding protein, a member of the steroidogenic acute regulatory protein (StARP) family as a lutein-binding protein and tubulin as a less specific, but higher capacity, site for carotenoid deposition. Dietary carotenoids are released from ingested foods after ester saponification if necessary and incorporated into lipid micelles. Scavenger receptor class B type 1 (SRB1), located on the surface of intestine cell, then facilitates uptake and transport to the portal circulation in the chylomicron fraction (Goti et al., Rigotti et al.).
Lutein transport mechanism
Earl Harrison, PhD, presented research about lutein’s transport mechanism to the eye. He said that lutein is carried by both HDL and LDL, while beta carotene is primarily carried by LDL. Zeaxanthin and mesozeaxanthin are taken up much more efficiently than lutein.
He and Thomas found that zeaxanthin and mesozeaxanthin are taken up more by HDL than LDL, whereas lutein is taken up more by LDL than HDL. For this reason, Harrison theorized that lutein does not compete with zeaxanthin or mesozeaxanthin due to the utilization of different cholesterol molecules and binding proteins.
Nutrients and cognitive function
Jirayu Tanprasertsuk, of the USDA Jean Mayer Human Nutrition Research Center on Aging at Tufts University, discussed the Georgia Centenarian Study on nutrient patterns associated with cognitive function in older adults without dementia.
The study population consisted of 47 donors, with an average age of 102 years. Most were female Caucasians (89%), and about half had dementia at the time of death. All of the tissue samples were measured for vitamin K, monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFAs), transfatty acids, saturated fatty acids (SFAs) and carotenoids. Both brain nutrient patterns and serum concentrations were analyzed.
It was found that serum concentrations of carotenoids, tocopherols and omega-3 fatty acids reflected brain concentrations when adjusted for sex, race, BMI, cognitive status, hypertension and diabetes. Tanprasertsuk stated that brain nutrition patterns in older adults without dementia were higher in omega-3 fatty acids, saturated fatty acids and carotenoids. The same individuals showed lower amounts of vitamin A, monounsaturated fatty acids and transfatty acids.
The discovery of higher levels of omega-3 fatty acids and carotenoids in nondemented human serum and tissue samples from older adults is promising for the future of carotenoid research and development in cognitive function.
Carotenoid intake lacking
Nearly all the researchers in attendance felt that the dietary amount of carotenoids consumed by individuals in most countries is well below the amounts desired. The lutein intake in the U.S. is very low. The 50th percentile of the U.S. population ingests only 1 mg of lutein daily, while the 95th percentile ingests only 5 mg/day to 7 mg/day.
According to Seddon and colleagues, 6 mg of lutein per day related to a 43% reduction in AMD. As such, Johnson and Erdman stated at the conference that the evidence is now sufficient to recommend lutein daily allowance (RDA) standards in the U.S. and Europe.
Nearly all components of visual performance are enhanced through increased carotenoid intake. The overlapping conclusions from research presenters at this conference once again emphasizes the need for practitioners to discuss the importance of carotenoid nutrition.
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- For more information:
- Kristin McArdle is a student intern from the Southern College of Optometry. She can be reached at email@example.com.
- David W. Nelson, OD, MBA, is in a private group practice in Madison, Wis. He can be reached at firstname.lastname@example.org.
Disclosures: McArdle reports no relevant financial disclosures. Nelson reports he is a consultant for MacuHealth.