New evidence continues to support dietary lutein, carotenoids, zeaxanthin, and meso-zeaxanthin as a means of inhibiting development of age-related macular degeneration (AMD). AMD is the leading cause of loss of vision in Western people over age 55.
A study published in 2010, in Archives of Biochemistry and Biophysics by the Department of Ophthalmology and Visual Sciences at University of Utah, found that production of singlet oxygen in the human retinal pigment epithelium (RPE) and choroid is prevented or reduced by lutein, zeaxanthin, and meso-zeaxanthin, which act as filters of short wavelength light. A combination of these carotenoids was found to be more effective in quenching singlet oxygen, which causes light-induced stress, than any of the carotenoids singularly at the same concentration.
It is key that when micronutrients are concerned, the whole is more than the sum of its parts.
In another crucial study published in the Journal of Lipid Research in 2008, researchers found that the xanthophyll carotenoids zeaxanthin and lutein, when compared to beta carotene, are preferentially taken up by retinal cells.
Also important in this research is the discovery of the way in which these two macular pigment carotenoids travel from the bloodstream to the eye in order to support eye health.
Past studies have shown the protein SR-BI (scavenger receptor class B, type 1) to function in the intestinal absorption of lutein and zeaxanthin. The authors of this study sought to discover whether SR-B1 could also be responsible for their transportation to the eye.
By observing the uptake of lutein, zeaxanthin, and beta carotene by human retinal pigment epithelial (RPE) cells, the authors found that lutein and zeaxanthin were more efficiently taken up by the RPEs than was beta carotene, and that the carotenoids were absorbed when the protein SR-BI was active. However, when compounds were added to inhibit the SR-BI, the uptake of zeaxanthin and beta-carotene was decreased by between 40 and 60 percent, whereas the inhibition of CD36 (another transport protein) made no effect. The researchers concluded that SR-BI does in fact aid in the transport and absorption of lutein and zeaxanthin in the eyes as well as the intestines.
Thus the study supports that lutein and zeaxanthin can help inhibit age-related macular degeneration by offering an explanation of the way in which these crucial nutrients are transported from bloodstream to eye.
A study published in the same year in Free Radical Biology Medicine showed that lutein in particular may decrease intracellular H(2)0(2) accumulation by scavenging superoxide and H(2)0(2) and the nuclear factor-kappaB (NF-kB) regulated inflammatory genes in lipopolysaccharide-stimulated macrophages. What this indicates is that dietary lutein could be significantly beneficial to those with increased risk of macular degeneration as well as Alzheimer’s, because the two diseases share an inflammatory component and many of the same genes.
This research builds on several other studies:
Study 1
In this one-year study, involving 90 patients at a midwest VA hospital, patients receiving lutein, lutein & other supplements, and placebo found improvement in the first two groups, but not the control. The authors noted that improvements in mean eye macular pigment optical density, visual acuity, and contrast sensitivity.
Source: Double-masked, placebo-controlled, randomized trial of lutein and antioxidant supplementation in the intervention of atrophic age-related macular degeneration: the Veterans LAST study (Lutein Antioxidant Supplementation Trial), Stiles, et al, Optometry. 2004 Apr;75(4):216-30.
Importantly, with adequate amounts of lutein available, lutein will be converted to meso-zeaxanthin by the eye for macula pigment. It is also important to note that the transport of lutein and zeaxanthin to the eye could be inhibited by excess body fat. Find out about dietary sources of lutein.
Study 2
Evidence continues to show that oxidative stress contributes to age-related maculopathy (ARM) and that consuming appropriate antioxidants such as zeaxanthin may protect against this condition.
The term maculopathy is associated with diseases of the macula, an area at the center of the retina that is associated with highly sensitive, accurate vision. Age-related macular degeneration (AMD) is an example of maculopathy.
A study published in the American Journal of Clinical Nutrition investigated the link between lower intakes of antioxidants and ARM. 828 healthy Irish participants between the ages of 20 and 60 years were analyzed for risk factors for ARM and dietary intake of relevant nutrients.
Researchers showed that several variables related to risk for ARM are associated with a relative lack of key nutrients in the diet. They determined that the most important and universal risk factor for ARM is a lack of dietary zeaxanthin.
Zeaxanthin is one of the two carotenoids contained within the retina of the eye. Ultraviolet radiation is absorbed by the lens, but visible or “blue” light penetrates to the retina, enabling us to see. Along with lutein, zeaxanthin absorbs the potentially harmful effects of blue light.
How can you ensure you are consuming zeaxanthin? Good dietary sources include green vegetables such as spinach, kale, turnip greens, collard greens, romaine lettuce, broccoli, zucchini, corn, garden peas and Brussels sprouts.