Lutein is a xanthophyll and one of 600 known naturally occurring carotenoids. Lutein is synthesized only by plants and like other xanthophylls is found in high quantities in green leafy vegetables such as spinach, kale and yellow carrots. In green plants, xanthophylls act to modulate light energy and serve as non-photochemical quenching agents to deal with triplet chlorophyll (an excited form of chlorophyll), which is overproduced at very high light levels, during photosynthesis. Xanthophylls are taken for nutritional supplementation, and also for treating dietary shortage or imbalance. Xanthophylls have antioxidant activity and react with active oxygen species, producing biologically active degradation products. They also can inhibit peroxidation of membrane phospholipids and reduce lipofuscin formation, both of which contribute to their antioxidant properties. Lutein is naturally present in the macula of the human retina. It filters out potentially phototoxic blue light and near-ultraviolet radiation from the macula. The protective effect is due in part, to the reactive oxygen species quenching ability of these carotenoids. Lutein is more stable to decomposition by pro-oxidants than are other carotenoids such as beta-carotene and lycopene. Lutein is abundant in the region surrounding the fovea, and lutein is the predominant pigment at the outermost periphery of the macula. Zeaxanthin, which is fully conjugated (lutein is not), may offer somewhat better protection than lutein against phototoxic damage caused by blue and near-ultraviolet light radiation. Lutein is one of only two carotenoids that have been identified in the human lens, may be protective against age-related increases in lens density and cataract formation. Again, the possible protection afforded by lutein may be accounted for, in part, by its reactive oxygen species scavenging abilities. Carotenoids also provide protection from cancer. One of the mechanisms of this is by increasing the expression of the protein connexin-43, thereby stimulating gap junctional communication and preventing unrestrained cell proliferation. Lutein was found to be present in a concentrated area of the macula, a small area of the retina responsible for central vision. The hypothesis for the natural concentration is that lutein helps protect from oxidative stress and high-energy light. Several studies show that an increase in macula pigmentation decreases the risk for eye diseases such as Age-related Macular Degeneration (AMD). There is also epidemiological evidence that increasing lutein and zeaxanthin intake lowers the risk of cataract development. Consumption of more than 2.4 mg of lutein/zeaxanthin daily from foods and supplements was significantly correlated with reduced incidence of nuclear lens opacities, as revealed from data collected during a 13- to 15-year period in the Nutrition and Vision Project (NVP).