Zeaxanthin

Zeaxanthin is one of the two carotenoids contained within the retina.

Within the central macula, zeaxanthin is the dominant component, whereas in the peripheral retina, lutein predominates.

Lutein and zeaxanthin have identical chemical formulas and are isomers, but they are not stereoisomers. The main difference between them is in the location of a double bond in one of the end rings. This difference gives lutein three chiral centers whereas zeaxanthin has two.

As a food additive, zeaxanthin is a food dye with E number E161h.

Isomers
Because of symmetry, the (3R,3'S) and (3S,3'R) stereoisomers of zeaxanthin are identical. Therefore, zeaxanthin has only three stereoisomeric forms. The (3R,3'S) stereoisomer is called meso-zeaxanthin.

The principal natural form of zeaxanthin is (3R,3'R)-zeaxanthin.

The macula mainly contains the (3R,3'R)- and meso-zeaxanthin forms, but it also contains much smaller amounts of the third (3S,3'S) form.

Relationship with diseases of the eye
There is epidemiological evidence of a relationship between low plasma concentrations of lutein and zeaxanthin on the one hand, and the risk of developing age-related macular degeneration (AMD) on the other. Some studies support the view that supplemental lutein and/or zeaxanthin help protect against AMD.

There is also epidemiological evidence that increasing lutein and zeaxanthin intake lowers the risk of cataract development.

On September 10, 2007, in a 6-year study, researchers, led by John Paul SanGiovanni of the National Eye Institute, Maryland found that Lutein and zeaxanthin (nutrients in eggs, spinach and other green vegetables) protect against blindness (macular degeneration), affecting 1.2 million Americans, mostly after age 65. Lutein and zeaxanthin reduce the risk of AMD (journal Archives of Ophthalmology). Foods considered good sources of the nutrients also include kale, turnip greens, collard greens, romaine lettuce, broccoli, zucchini, corn, garden peas and Brussels sprouts.

Natural occurrence
Zeaxanthin is one of the most common carotenoid alcohols found in nature. It is the pigment that gives corn, saffron, and many other plants their characteristic color. Zeaxanthin breaks down to form picrocrocin and safranal, which are responsible for the taste and aroma of saffron.