Nutrition for vision and cognition
Breakthrough data is accumulating that link levels of the three carotenoids in the macula to cognitive function
The story of the effects of dietary supplementation with carotenoids found in the human macula is evolving as research in this area continues, according to John M. Nolan, PhD.
Available evidence shows that macular carotenoid supplementation has potential ocular health and visual function benefits for both eyes with age-related macular degeneration (AMD) and healthy (non-diseased) eyes. Clinical study findings also support the use of a formulation containing all three carotenoids that are present as macular pigments—meso-zeaxanthin (10mg), lutein (10mg), and zeaxanthin (2mg)—rather than just lutein and zeaxanthin. In addition, breakthrough data are accumulating that link levels of the three carotenoids in the macula to cognitive function, said Dr. Nolan, Director of the Nutrition Research Centre Ireland (NRCI; www.nrci.ie) and Principal Investigator of the Macular Pigment Research Group (MPRG) within that centre.
“There is a clear rationale for macular carotenoid supplementation and data to show that it increases macular pigment levels, improves visual function, and reduces AMD progression,” he commented.
“Now there is also evidence that the implications of optimising nutrition with macular carotenoid supplementation goes beyond ophthalmology.”
Of the approximately 700 carotenoids present in nature, meso-zeaxanthin, lutein, and zeaxanthin are uniquely found at the central retina where they are collectively know as macular pigment at this sensitive vision-mediating tissue in the human eye. Macular pigment exhibits several key properties, which make it ideal to protect the retina and enhance visual function. First, the carotenids protect against photo-oxidative tissue damage by absorbing (filtering) short-wavelength (blue) light. Secondly, the antioxidant properties of MP means that the carotenoids that scavenge reactive oxygen species protect the retina from oxidative damage. In addition, the optical properties of macular pigment are very important for visual performance. Indeed, the pre-receptoral location ensures that it filters blue light before it reaches the central retina. This reduces chromatic aberration and light scatter and thus enhances visual performance by enhancing contrast sensitivity.
There is also evidence that the implications of optimising nutrition with macular carotenoid supplementation goes beyond ophthalmology
Benefits in AMD
Dr. Nolan said that AREDS2 demonstrated a striking benefit of supplementation with lutein and zeaxanthin for reducing risk for progression to advanced AMD among participants who had low dietary intake of these carotenoids.
“Health care professionals who are making recommendations to patients about carotenoid supplementation should know that even the average person with a healthy diet rich in fruits and vegetables is not consuming enough of the macular carotenoids to change tissue levels,” he noted.
However, studies conducted by Dr. Nolan and colleagues indicate there are benefits for carotenoid supplementation using a formulation containing meso-zeaxanthin in addition to lutein and zeaxanthin, and particularly in a 10:10:2 mg/day ratio (meso-zeaxanthin:lutein:zeaxanthin) of the three carotenoids. An initial trial randomised 67 patients with early AMD to treatment with supplements containing 1) lutein 20 mg + zeaxanthin 0.86 mg; 2) meso-zeaxanthin 10 mg + lutein 10 mg + zeaxanthin 2 mg; or 3) meso-zeaxanthin 17 mg + lutein 3 mg + zeaxanthin 2 mg. After 36 months, all groups showed an increase in macular pigment as measured by macular pigment optical density (MPOD), but supplementation with meso-zeaxanthin was necessary for pigment enrichment in the central macula where meso-zeaxanthin is found and for optimal visual performance to be achieved.
Other analyses showed that contrast sensitivity enhancement was best in the group receiving the triple carotenoid supplement containing 10 mg meso-zeaxanthin. Furthermore, no patient receiving a triple carotenoid formula progressed to visually consequential AMD during the 3-year study. Putting those results into context, Dr. Nolan noted that in a previous trial where patients with early AMD received only lutein, half developed advanced AMD within 3 years.
Dr. Nolan also discussed the European Research Council-funded Central Retinal Enrichment Supplementation Trials. The project consists of two studies, and the first is already completed. It randomised individuals with healthy eyes but low central macular pigment to placebo or a supplement containing meso-zeaxanthin 10 mg, lutein 10 mg, and zeaxanthin 2 mg.
CHANGES IN CS OVER TIME
The primary endpoint analysis showed contrast sensitivity at 6 cycles per degree was significantly improved after 12 months in the patients consuming the carotenoid formulation. Statistically significant differences favoring the supplement group were also achieved in a number of secondary outcome measures that are being investigated, including in several cognitive function endpoints. Professor Nolan quoted his close colleague Professor Stephen Beatty, saying that this was the first discovery since the invention of spectacles that we have identified a way to improve vision in the healthy eye.
Carotenoids and the brain
Discussing the potential for macular carotenoid supplementation to improve cognitive function, Dr. Nolan noted that macular pigments are present in the human brain where their levels correlate directly with the amounts found in the macula.
Citing findings conducted by his research group, Dr. Nolan said that analyses of data from about 4500 adults aged ≥50 years enrolled in The Irish Longitudinal Study on Aging demonstrated an association between having higher levels of macular pigment and better performance on a variety of tests of cognition.
Other studies focusing on patients with Alzheimer’s disease showed several novel and important findings, Dr. Nolan said.
“We were the first to measure macular pigment in patients with Alzheimer’s disease. We found the levels to be very low, and we also found that about half of the patients with Alzheimer’s disease had AMD,” he reported.
“In addition, we demonstrated carotenoid supplement was effective for enriching the macular pigment levels and was associated with improved contrast sensitivity. Our research is continuing and is focusing on the implications of carotenoid supplementation for both visual and cognitive performance. This evidence means that carotenoid nutrition must now become part of eye care. We cannot ignore the importance of these findings for people patients who want to optomise their vision and reduce risk against AMD”