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Lutein, Zeaxanthin and AMD Risk

The low values of macular pigment density seen in some people, coupled with the age-related decline of natural defenses in the retina and RPE can increase oxidative stress, a risk factor for AMD. AMD risk is thought to be further increased by exposure to blue (short-wavelength) light, although the results of observational studies have been conflicting.

One of the observational studies reports that estimated lifetime blue light exposure increased the risk of neovascular AMD specifically in individuals with low plasma levels of antioxidants, including zeaxanthin. However, experiments to evaluate the relationship of the macular pigment xanthophylls (lutein and zeaxanthin) to light damage and macular disease have been few, due to a lack of appropriate animal models. Only higher primates have a macula lutea, with its high foveal concentration of macular pigment.

Working with a unique set of rhesus monkeys raised on lutein and zeaxanthin-free diets, a research team has now looked at the effects of macular pigment absence – followed by xanthophyll supplementation – on blue light damage. The researchers also examined whether a deficiency of omega-3 fatty acids affects sensitivity to blue light as well.

Study Design and Methods

The study included 8 rhesus monkeys with no lifelong intake of xanthophylls and no detectable macular pigment. Four of the monkeys had low omega-3 intake and 4 had adequate dietary intake.

Retinas received 150 μm-diameter exposures of low-power 476 nm laser light either at 0.5 mm [~2(o)] eccentricity, adjacent to the macular pigment peak, or parafoveally at 1.5 mm [~6(o)]. Exposures of xanthophyll-free animals were repeated after supplementation with pure lutein or zeaxanthin for 22-28 weeks.

Visible lesion areas were plotted as a function of exposure energy, with greater slopes of the regression lines indicating greater sensitivity to damage. The results were compared to data from control animals with typical levels of xanthophylls and omega-3 in their diets and retinas.

Results

For control animals with normal macular pigment, the fovea was less sensitive to blue light damage than the parafovea. However in the monkeys lacking macular pigment, fovea and parafovea were equally vulnerable.

After supplementation, foveal protection in xanthophyll-free animals did not differ from controls. And, like controls, the fovea was now less sensitive to damage than the parafovea.

In the parafovea (but not the fovea), animals low in omega-3 fatty acids showed greater sensitivity to damage compared to those with adequate omega-3.

Comments

These findings confirm the photo-protective effect of lutein and zeaxanthin in the fovea where their con-centration is greatest, and indicate that omega-3 fatty acids lessen damage in the parafovea. Although the study showed protection against acute blue light damage, it seems probable that these nutrients would also protect the macula against chronic blue light exposure.

The omega-3 fatty acid DHA is present at exceptionally high levels in the retina, particularly in photoreceptor outer segment membranes. There are a number of ways by which DHA could act to lessen blue light damage: it serves as the precursor for neuroprotective factors and helps counter inflammation. In addition DHA helps block abnormal vessel growth (see EduFacts Vol. 12 No. 1).

“Our results”, conclude the study authors, “offer hope that good nutrition, augmented by supplementation when appropriate, can contribute to reduction of risk for AMD, especially for persons with reduced macular xanthophyll levels due to retinal disease, poor diet, or genetic predisposition”.

References

Barker FM, et al. Nutritional Manipulation of Primate Retinas. V: Effects of Lutein, Zeaxanthin and n–3 Fatty Acids on Retinal Sensitivity to Blue Light Damage. IOVS Papers in Press. Published on January 18, 2011 as Manuscript iovs.10-5898