Xanthophyll consists of lutein, zeaxanthin, and zeaxanthin’s stereoisomer, meso-zeaxanthin, which are compounds that play a role in preserving the structure and function of the retina. They also function as antioxidants and can absorb blue light.
Writing in Nutrition Reviews, the researchers highlighted that intake of xanthophyll-rich foods or supplements has shown to improve eye health, but more benefits, especially improvement in visual acuity was seen in those with eye diseases.
Forty-three relevant research papers were sieved out from databases including PubMed, Scopus, Embase, CINAHL, Cochrane, and Web of Science for this meta-analysis and systematic review.
The goal of the meta-analysis was to evaluate the effect of intake of xanthophyll-rich food and supplements on the five major visual outcomes, including MPOD, visual acuity, photostress recovery, contrast sensitivity, and glare sensitivity.
Out of the 43 papers, 37 were intervention with xanthophyll supplementation, five with dietary interventions, and one compared the effect of dietary goji berry consumption with lutein and zeaxanthin supplementation.
The study duration ranged from eight weeks to over 300 weeks. Most studies had an intervention period of 10 to 49 weeks.
Findings showed that xanthophyll intake has enhanced macular pigment optical density (MPOD) in healthy and diseased individuals.
However, there was greater increase in MPOD in individuals with eye disease, which may be due to their lower baseline MPOD values as compared to the healthy individuals
MPOD is a direct measurement of the density of xanthophyll pigments in macula and can serve as a biomarker for eye diseases.
Therefore, the researchers pointed out that the increase in MPOD may indicate the effectiveness of xanthophyll intake in lowering the risks of eye diseases.
“Dietary xanthophyll is transported from the choroidal blood supply through the retinal pigment epithelium to the retina, where the pigments are accumulated at the highest density,” the researchers explained.
Secondly, the intake of xanthophyll has shown to improve visual acuity, but this was only seen in individuals with eye diseases, with no effect seen in healthy individuals.
“Increased xanthophyll accumulation has been suggested to improve visual acuity by attenuating the dispersion and chromatic distortion caused by the different light wavelengths,” the researchers said.
Thirdly, there was positive correlation not amounting to a significant change between the improvements in MPOD and serum lutein levels.
The researchers explained that in this case, the bioavailability of xanthophyll needs to be taken into consideration.
Xanthophyll is of low bioavailability due to its hydrophobic nature and low solubility in digestion fluids.
The bioavailability of xanthophyll can be increased by co-consuming dietary fat with xanthophyll-rich foods, such as unsaturated fatty acids, as well as other antioxidants such as vitamin C and polyphenols.
The study was funded by the National University of Singapore.
Source: Nutrition Reviews
Effect of xanthophyll-rich food and supplement intake on visual outcomes in healthy adults and those with eye disease: a systematic review, meta-analysis, and meta-regression of randomized controlled trials
Authors: Hu W, Shankar P, Yao Y, Su X, Kim JE.