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.
Health benefits for 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 [1-7]. Several studies also show that an increase in macula pigmentation decreases the risk for eye diseases such as Age-related Macular Degeneration (AMD) [8-10].
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, fortification via a sublingual spray ensures maximum benefit to the eyes. 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 levels of 6 mg/day . The only definitive side effect of excess lutein consumption is the same observed for β-carotene overdose, namely bronzing of the skin (carotenodermia). The normal levels of Lutein found in a daily vitamin tablet can be as low as 0.25mg.
The functional difference between the benefits of 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.