Lutein and zeaxanthin belong to the class of carotenoids known as xanthophylls and both 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. They are both polyisoprenoids containing 40 carbon atoms and cyclic structures at each end of their conjugated chains. The main difference between them is in the location of a double bond in one of the end rings giving lutein three chiral centers as opposed to two in zeaxanthin (see structure below).

Zeaxanthin Structure

Lutein and zeaxanthin are phytochemicals found most often in leafy green vegetables, but also in other fruits and vegetables. Chicken egg yolks are a rich food source of lutein and zeaxanthin; he average amount of lutein in chicken egg yolk is approximately 290 micrograms per yolk, and the average amount of zeaxanthin, approximately 210 micrograms per yolk.

Xanthophylls 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.