Irish and UK-based researchers reported recently that a combination of zeaxanthin, lutein, and meso-zeaxanthin may be produce better results that a combination of lutein and zeaxanthin.
“In other words, it appears that a formulation containing all three macular carotenoids was more efficacious in terms of achieving a higher concentration of circulating levels of total macular carotenoids, thereby potentially optimizing the bioavailability of these compounds for capture by the target tissue (retina),” they wrote in the British Journal of Nutrition.
Challenging this hypothesis
However, in a letter to NutraIngredients-USA, experts from Kemin, including Richard Roberts, PhD, Justin Green, PhD, and Samanta Maci, MS, said that: “Kemin submits that the well-established science on this important topic and the limitations of this study do not support this statement.
“Contrary to the hypothesis that all three carotenoids may be required in eye health formulations, there is an extensive body of established scientific literature consistently reporting that supplementation with lutein and zeaxanthin in the absence of meso-zeaxanthin (MZ) increases macular pigment (MP) and improves visual function in healthy subjects or patients suffering from AMD or other eye diseases.
“There is no evidence proving that MZ supplementation or high serum MZ translates to high MZ in the retina, since in the few MZ supplementation studies conducted up to now, lutein (L) and zeaxanthin (Z) were also always present in the MZ formulations evaluated.
“Furthermore, MP measurement does not discriminate among the three macular carotenoids but instead provides a single, collective measurement of pigment density based upon the combined presence in the retina of L, Z and MZ. Therefore, an increase in MP after supplementation with MZ, L and Z does not necessarily mean that it is the MZ that has contributed to that increase.”
Roberts, Green and Maci added that lutein and zeaxanthin cannot be synthesized de-novo in mammals so their presence in the macula is due to the ingestion of common foods rich in these two carotenoids.
Meso-zeaxathin, they noted, is not present in the human diet and has only recently been introduced via supplementation. This carotenoid originates from lutein metabolism in the macula, they said.
“Accordingly, a proper intake of lutein and zeaxanthin without MZ already supplies the eye with the three carotenoids and can increase macula pigment.”
Apples and pears
“It is known that lutein pharmacokinetics is not linear and that the capacity for intestinal absorption may become limited with increasing doses of carotenoids. The cited study clearly shows that high MZ is not very well absorbed by the body and that a high MZ can instead have the adverse effect of impairing L and Z absorption.
“The researchers compared two commercially available supplements and one experimental supplement formula which were manufactured in different places by different companies with different manufacturing methods and equipment. These three supplements may have contained different excipients and potentially even different softgel matrices.
“This is an important and relevant limitation for any trial designed to assess and compare the absorption and bioavailability of ingredients, since dissolution of the capsule and its contents may have a profound impact on absorption of the ingredients under evaluation. It is impossible to verify if the increase in serum lutein observed in group 2 is impacted by the MZ content or whether it is a result of formulation differences.
“Importantly, the amount of total carotenoids in serum is relevant only if all of these carotenoids are taken up in the retina; if they increase the density of the MP; and, of utmost importance, benefit visual function and health.
“One could also supplement with beta-carotene or lycopene to achieve higher serum carotenoids, but such an increase would be unlikely to increase retinal carotenoids or visual performance because those carotenoids are not deposited in the macula.
“There is MZ in the retina, but it occurs via the body’s own metabolic processes without MZ in the diet or the serum.
“It is established from primate studies that MZ is there as a result of conversion from lutein, and contrary to the above claim, does not have to be introduced from an exogenous source to accumulate in the retina and provide eye health benefits.”