Lutein, Zeaxanthin, and meso-zeaxanthin – the three exclusive carotenoids found in the eye – have been well-studied as dietary ingredients correlated with healthy eyesight, highlighted by large-scale clinical trials, due to their role in preventing age-related macular degeneration. Along with their antioxidant activity within the eye, these pigments also protect the eye by filtering out blue light.
 
In a recent review appearing in Advances in Nutrition, researchers analyzed data from 46 clinical studies, concluding that evidence is compelling that adults with higher concentrations of these three carotenoids within the macula of their eyes are significantly more likely to have healthy eyesight.
 
Because humans can’t synthesize lutein and zeaxanthin and must obtain them from their diet, the authors of the study set the goal of establishing a minimal daily intake for the two nutrients that would confer optimal benefits to eyesight, as there are currently no dietary recommendations on the daily intake of lutein and zeaxanthin.
 
The search for literature, conducted in July 2020, utilized the Ovid MEDLINE, Cochrane Central Register of Studies, and Commonwealth of Agriculture Bureau databases, and all studies included were human clinical trials involving healthy adult participants. The dosage categories evaluated were <5 mg daily, 5 to 20 mg.
 
For the lowest dosage, the authors said that their confidence in the ability for it to increase macular pigment optical density (MPOD) was very low. For the moderate dosage, six trials were evaluated, and it was found that dosages in this range increased MPOD by 0.04 units on average following lutein/zeaxanthin supplementation. Lastly, the high-dosage supplementation periods across the studies increased MPOD by 0.11 units on average in adults with healthy eyes, establishing a dose-response relationship between supplementation and MPOD.
 
The authors concluded that supplementation with lutein and zeaxanthin at doses of over 5 mg daily were sufficient in increasing MPOD in adults with healthy eyesight, and there were no differences in supplements with or without meso-zeaxanthin, a form of the carotenoid which is formed at the macula by metabolic transformations of ingested carotenoids.
 
However, they concluded that further research is warranted to determine the minimum dose and duration of lutein/zeaxanthin needed to induce a clinically important change in MPOD or visual function.