In the analysis, published last week in the journal Nutrients, authors looked at trials that used the three carotenoids. Doing a search on terms that included xanthophyll carotenoids, lutein, zeaxanthin and meso-zeaxanthin, the authors came up with a potential field of 2,456 relevant publications. After reviewing the abstracts and weaning out duplicate publications, 133 articles were retrieved for detailed evaluation. Of these, many were excluded for various reasons including the lack of control group or lack of information about the standard deviations in the data, leaving 20 randomized, controlled trials that were included in the meta-analysis. The researchers, who are associated with five different medical research facilities in China, said the resulting field encompassed 938 patients with age-related macular degeneration (AMD) and 826 healthy subjects.
The researchers looked at the effects of xanthophyll carotenoid supplementation on the amount of macular pigment (macular pigment optical density or MPOD) in the macula, the specialized region of the retina where these yellowish pigments are concentrated. A dearth of these pigments has been associated with AMD and more recent research suggests that xanthophyll supplementation can actually improve certain parameters of visual performance among subjects who have yet to exhibit any AMD symptoms but who may have lower-than-average levels of MP. The researchers said the results form the publicized trials showed that overall xanthophyll carotenoid supplementation boosted MPOD in AMD patients and in healthy subjects in a dose-dependent relationship.
There has been some debate within the eye health ingredient community on the subject of the necessity of including meso-zeaxanthin in this trio. Proponents of this view argue that dietary sources of meso-zeaxanthin are few and far between, and while it is indisputable that this carotenoid is present in the MP, they argue that the body fixes it there by synthesizing it out of lutein.
Making the case for all three
The meta-analysis authors, while not weighing in specifically on that debate, did point to the importance of that molecule’s function in the eye. “[Meso-zeaxanthin] has the ability to protect against chronic and cumulative eye damage through its capacity to filter the most energetic and potentially damaging wavelengths of visible light and to neutralize free radicals produced by oxidative stress,” they wrote. The results of their analysis was unequivocal: Formulations that included meso-zeaxanthin performed better. “Stratified analysis showed a greater increase in MPOD among trials supplemented and combined with meso-zeaxanthin,” they wrote.
“Our results showed that the carotenoids supplementation significantly increased the level of MPOD and the inclusion of meso‐zeaxanthin resulted in a greater increase in macular pigment compared to supplements lacking this central carotenoid. The increment in MPOD was positively correlated with changes in blood xanthophyll carotenoids concentration. Furthermore, supplementation with these carotenoids for longer than 12 months, a higher dose and the three carotenoids in combination were more effective on MPOD augmentation,” they concluded.
Irish researcher John Nolan PhD, of the Waterford Institute of Technology, has worked on meso-zeaxanthin and its sister xanthophyll carotenoids for more than twenty years. He has come through the fire of the debates about what the best combination of these ought to be for optimal eye health supplementation and has long been a supporter of meso-zeaxanthin for eye health formulations.
“This question has now been dealt with by published science. The notion (and this is a notion) that retinal meso-zeaxanthin is wholly and solely derived from dietary lutein remains unclear and not fully tested,” Nolan said.
“Lutein, Zeaxanthin and Meso-zeaxanthin Supplementation Associated with Macular Pigment Optical Density.”
2016 Jul 12;8(7). pii: E426
Authors: Ma L, et al