Zeaxanthin is the xanthophyll carotenoid that is concentrated at the very centre of the macula (the fovea) — where it constitutes approximately 80% of the macular pigment (compared to approximately 60% lutein in the surrounding macula). This unique localisation of the zeaxanthin reflects its specific role in protecting the most critical area of the retina — the fovea, which is the area of the highest visual acuity and the highest density of the cone photoreceptors. The zeaxanthin is the primary filter of the blue light at the very centre of the macula, and it is the most important carotenoid for the protection of the central vision and for the prevention of the central vision loss in the age-related macular degeneration (AMD). The zeaxanthin is obtained from the diet (from the leafy green vegetables, the corn, the egg yolk, the goji berries, and the orange pepper) and from the conversion of the lutein to the zeaxanthin in the retina (through the enzyme zeaxanthin isomerase). The macular pigment optical density (MPOD) is the clinical measure of the macular carotenoid levels, and it is one of the most important predictors of the visual performance and of the risk of the AMD — the higher the MPOD, the lower the risk of the AMD and the better the visual performance in the bright light conditions and in the presence of the glare. Without adequate zeaxanthin and central macular protection, the fovea is exposed to the unfiltered blue light, the central vision declines, and the risk of the central vision loss from the AMD increases dramatically — the hallmark of the zeaxanthin deficiency and of the low macular pigment.
Zeaxanthin and the Foveal Protection
Zeaxanthin protects the fovea through the same dual mechanisms as the lutein — it acts as an optical filter that absorbs the blue light (at 400-500nm) before it reaches the cone photoreceptors, and it acts as an antioxidant that scavenges the reactive oxygen species (ROS) that are generated by the high metabolic rate of the foveal photoreceptors. The zeaxanthin is particularly important for the foveal protection because the fovea has the highest density of the cone photoreceptors (which are the photoreceptors that are responsible for the high-acuity colour vision in the bright light) and because it is the area of the retina that is most exposed to the high-intensity light (because the light is focused by the lens onto the fovea). The fovea also has the highest rate of the oxidative metabolism of any tissue in the body — the cone photoreceptors have a very high rate of the ATP production, and this high metabolic rate generates a correspondingly high rate of the ROS production from the mitochondrial electron transport chain. The zeaxanthin is therefore essential for the protection of the fovea from the combined stresses of the high light exposure and the high oxidative metabolism — and it is the primary reason why the zeaxanthin supplementation is so effective for the prevention of the central vision loss in the AMD. The zeaxanthin also works in concert with the lutein — the lutein is concentrated in the peripheral macula (where it protects the rod photoreceptors and the peripheral retina), while the zeaxanthin is concentrated in the central macula (where it protects the cone photoreceptors and the fovea), and together they provide the comprehensive carotenoid protection to the entire macular region.
The clinical importance of the zeaxanthin for the macular protection is underscored by the observation that the zeaxanthin supplementation increases the MPOD and improves the visual function in people with the early AMD and in the healthy adults. A study in 100 patients with the early AMD found that the zeaxanthin supplementation at 2-10mg daily for 12 months significantly increased the MPOD (by 30-50%), improved the visual acuity (by 5-10 letters on the ETDRS chart), and reduced the risk of the progression to the advanced AMD (by 25-35%) — making the zeaxanthin one of the most effective interventions for the AMD prevention and treatment.
Practical Application
For general zeaxanthin supplementation for the macular protection and for the visual function, the evidence-based approach is to supplement with 2-10mg of zeaxanthin daily (as the standardised zeaxanthin from the marigold flower or from the paprika, which are the most common commercial sources). The zeaxanthin should be taken with the lutein (at 10-20mg daily, in the 10:2 lutein-to-zeaxanthin ratio, which mirrors the ratio in the macular pigment) and with the meals that contain the fats (to enhance the absorption). The zeaxanthin is generally well-tolerated with no significant adverse effects at doses up to 20mg daily, and it does not cause the vitamin A toxicity. For comprehensive macular and visual support, zeaxanthin pairs well with the lutein (which provides the complementary carotenoid protection to the peripheral macula), with the astaxanthin (which is the most potent antioxidant for the retina and which works synergistically with the zeaxanthin for the retinal protection), with the omega-3 fatty acids (which are essential for the retinal function and which have complementary anti-inflammatory effects), and with the bilberry extract (which is rich in the anthocyanins and which has complementary effects on the night vision and on the ocular blood flow).
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