Zeaxanthin is a yellow-colored lipid-soluble xanthophyll, which is also an oxidized hydroxy derivative of beta-carotene. This biochemical, a strong antioxidant and one of two yellow carotenoids found in the retina, is abundant in spinach, collard greens, and corn. It is widely believed that zeaxanthin acts to filter and shield harmful blue light from the eye and protect against age-related macular degeneration, the leading cause of blindness in people over 65.
Popeye, the popular cartoon character known for his timely consumption of spinach, was correct in his assumption that this unpopular vegetable is healthy eating. So was mom. Ounce for ounce, spinach contains more than twice as much zeaxanthin and more than 60 times as much lutein as yellow corn. These carotenoids are now believed to protect against development of cataracts, and may have other health benefits as well.
Lutein and zeaxanthin are members of the carotenoid family, a family best known for another one of its members, beta-carotene. They are natural fat-soluble yellowish pigments found in some plants, algae and photosynthetic bacteria. They serve as accessory light-gathering pigments and to protect these organisms against the toxic effects of ultra-violet radiation and oxygen. They also appear to protect humans against phototoxic damage. Lutein and zeaxanthin are found in the macula of the human retina, as well as the human crystalline lens. They are thought to play a role in protection against age-related macular degeneration (ARMD) and age-related cataract formation. They may also be protective against some forms of cancer. These two carotenoids are sometimes referred to as macular yellow, retinal carotenoids or macular pigment.
Lutein and zeaxanthin belong to the xanthophyll class of carotenoids, also known as oxycarotenoids. The xanthophylls, which in addition to lutein and zeaxanthin, include alpha-and beta-cryptoxanthin, contain hydroxyl groups. This makes them more polar than carotenoids, such as beta-carotene and lycopene, which do not contain oxygen. Although lutein and zeaxanthin have identical chemical formulas and are isomers, they are not stereoisomers, as is sometimes believed. They are both polyisoprenoids containing 40 carbon atoms and cyclic structures at each end of their conjugated chains. Also, they both occur naturally as all-trans (all-E) geometric isomers. The principal difference between them is in the location of a double bond in one of the end rings. This difference gives lutein three chiral centers rather than the two that are found in zeaxanthin.
Zeaxanthin has two chiral centers and therefore, 22 or 4 stereoisomeric forms. One chiral center is the number 3 atom in the left end ring, while the other chiral center is the number 3' carbon in the right end ring. One stereoisomer is (3R,3'R)-zeaxanthin; another is (3S-3'S)-zeaxanthin. The third stereoisomer is (3R,3'S)-zeaxanthin, and the fourth, (3S,3'R)-zeaxanthin. However, since zeaxanthin, in contrast to lutein, is a symmetric molecule, the (3R,3'S)-and (3S,3'R)-stereoisomers are identical. Therefore, zeaxanthin has only three stereoisomeric forms. The (3R,3'S)-or (3S,3'R)-stereoisomer is called meso-zeaxanthin.
The principal natural form of zeaxanthin is (3R,3'R)-zeaxanthin. (3R,3'R)-and meso-zeaxanthin are found in the macula of the retina, with much smaller amounts of the (3S,3'S)-stereoisomer. It is thought that meso-zeaxanthin in the macula is formed from (3R,3'R,6'R)-lutein. Zeaxanthin is also known as beta, beta-carotene-3,3'-diol, all-trans-beta-carotene-3,3'-diol, (3R,3'R)-dihydroxy-beta-carotene (the principal natural stereoisomer), zeaxanthol and anchovyxanthin. Its molecular formula is C40H56O2 and its molecular weight is 568.88 daltons. Zeaxanthin is the principal pigment of yellow corn zea mays L, from which its name is derived. It is also produced by certain bacteria, such as Flavobacterium multivorum, which are yellow in color.
Food sources of lutein and zeaxanthin, include corn, egg yolks and green vegetables and fruits, such as broccoli, green beans, green peas, brussel sprouts, cabbage, kale, collard greens, spinach, lettuce, kiwi and honeydew. Lutein and zeaxanthin are also found in nettles, algae and the petals of many yellow flowers. In green vegetables, fruits and egg yolk, lutein and zeaxanthin exist in non-esterified forms. They also occur in plants in the form of mono-or diesters of fatty acids. For example, lutein and zeaxanthin dipalmitates, dimyristates and monomyristates are found in the petals of the marigold flower (Tagetes erecta). Many of the marketed lutein nutritional supplements contain lutein esters, with much smaller amounts of zeaxanthin esters, which are derived from the dried petals of marigold flowers.