Lutein
Lutein (LOO-teen) (from Latin lutea meaning "yellow") is one of over 600 known naturally occurring carotenoids. Found in green leafy vegetables such as spinach and kale, lutein is employed by organisms as an antioxidant and for blue light absorption. Lutein is covalently bound to one or more fatty acids present in some fruits and flowers, notably marigolds (Tagetes). Saponification of lutein esters yields lutein in approximately a 2:1 weight-to-weight conversion.
Lutein is a lipophilic molecule and is generally insoluble in water. The presence of the long chromophore of conjugated double bonds (polyene chain) provides the distinctive light-absorbing properties.  The polyene chain is susceptible to oxidative degradation by light or heat and is chemically unstable in acids.
The principal natural stereoisomer of lutein is         
(3R,3'R,6'R)-beta, epsilon-Carotene-3,3'-diol.

# As a pigment
This xanthophyll, like its sister compound zeaxanthin, has primarily been used as a natural colorant due to its orange-red color. Lutein absorbs blue light and therefore appears yellow at low concentrations and orange-red at high concentrations.
Lutein was traditionally used in chicken feed to provide the yellow color of broiler chicken skin.  Polled consumers viewed yellow chicken skin more favorably than white chicken skin. Such lutein fortification also results in a darker yellow egg yolk. Today the coloring of the egg yolk has become the primary reason for feed fortification.  Lutein is not used as a colorant in other foods due to its limited stability, especially in the presence of other dyes.

# Role in human eyes
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. Various research studies have shown that a direct relationship exists between lutein intake and pigmentation in the eye . Several studies also show that an increase in macula pigmentation decreases the risk for eye diseases such as Age-related Macular Degeneration (AMD) . The only randomized clinical trial to demonstrate a benefit for lutein in Macular Degeneration was a small study, in which the authors concluded that more study was needed.
Lutein is a natural part of human diet when fruits and vegetables are consumed. For individuals lacking sufficient lutein intake, lutein-fortified foods are available, or in the case of elderly people with a poorly absorbing digestive system, a sublingual spray is available. As early as 1996, lutein has been incorporated into dietary supplements.  While no recommended daily allowance currently exists for lutein as for other nutrients, positive effects have been seen at dietary intake levels of 6 mg/day Template:Ref N. The only definitive side effect of excess lutein consumption is bronzing of the skin (carotenodermia).
The functional difference between lutein (free form) and lutein esters is not entirely known. It is suggested that the bioavailability is lower for lutein esters, but much debate continues.
As a food additive, lutein has the E number E161b.
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.

# Commercial value
The Lutein market is segmented into Pharmaceutical, Nutraceutical, Food, Pet Foods and Animal Feed and Fish Feed. The Pharmaceutical market is estimated to be about US $ 190 Million, Nutraceutical and Food is estimated to be about US $ 110 Million. Pet foods and other applications are estimated at US $ 175 Million annually.  Apart from the customary Age related Macular Degeneration applications , newer applications are emerging in Cosmetics, Skin Care and as an Antioxidant.  It is one of the fastest growing areas of the $ 2 Billion carotenoid market Template:Ref N. There are several lutein ester suppliers, but few pure lutein (Free Form) suppliers due primarily to patent protections on obtaining purified Lutein from natural products, namely marigolds. Companies like Indus Biotech Pvt. Ltd, OmniActive Health Technologies and Kemin Industries have patents.  The market size of lutein is anticipated to grow at an average annual growth rate of over 22%.