Lutein is a xanthophyll and one of 600 known naturally occurring carotenoids. Lutein is
synthesized only by plants and like other xanthophylls is found in high quantities in
green leafy vegetables such as spinach, kale and yellow carrots. In green plants, xanthophylls
act to modulate light energy and serve as non-photochemical quenching agents to deal
with triplet chlorophyll, which is overproduced at very high light levels, during photosynthesis.
See xanthophyll cycle for this topic. Lutein is obtained by animals directly or
indirectly, from plants. Lutein is apparently employed by animals as an antioxidant and
for blue light absorption. Lutein is found in egg yolks and animal fats. In addition
to coloring yolks, lutein causes the yellow color of chicken skin and fat, and is used
in chicken feed for this purpose. The human retina accumulates lutein and zeaxanthin.
The latter predominates at the macula lutea while lutein predominates elsewhere in the
retina. There, it may serve as a photoprotectant for retina from the damaging effects of free
radicals produced by blue light. The principal natural stereoisomer of lutein
is-beta,epsilon-carotene-3,3′-diol. Lutein is a lipophilic molecule and is generally
insoluble in water. The presence of the long chromophore of conjugated double bonds provides
the distinctive light-absorbing properties. The polyene chain is susceptible to oxidative
degradation by light or heat and is chemically unstable in acids.
Lutein is present in plants as fatty-acid esters, with one or two fatty acids bound
to the two hydroxyl-groups. For this reason, saponification of lutein esters to yield free
lutein may yield lutein in any ratio from 1:1 to 1:2 molar ratio with the saponifying
fatty acid. Lutein is isomeric with zeaxanthin, differing
only in the placement of one double bond.
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 improve the 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 concentrated in the
macula, a small area of the retina responsible for central vision. The hypothesis for the
natural concentration is that lutein helps keep the eyes safe from oxidative stress and
the high-energy photons of blue light. Various research studies have shown that a direct
relationship exists between lutein intake and pigmentation in the eye.
Lutein may play a role in Haidinger's brush, an entoptic phenomenon that allows humans
to detect polarized light. Macular degeneration
Several studies show that an increase in macula pigmentation decreases the risk for eye diseases
such as age-related macular degeneration. The only randomized clinical trial to demonstrate
a benefit for lutein in macular degeneration was a small study, in which the authors concluded
that visual function is improved with lutein alone or lutein together with other nutrients
and also that more study was needed. There is epidemiological evidence of a relationship
between low plasma concentrations of lutein and zeaxanthin, and an increased risk of developing
age-related macular degeneration. Some studies support the view that supplemental lutein
and/or zeaxanthin help protect against AMD. In 2007, in a six-year study, John Paul SanGiovanni
of the National Eye Institute, Maryland found that lutein and zeaxanthin protect against
blindness, affecting 1.2 million Americans, mostly after age 65. Lutein and zeaxanthin
reduce the risk of AMD. In 2013, findings of the Age-related Eye Disease
Study 2 were reported in JAMA; AREDS2 was a five-year study designed to test whether
the original AREDS formulation that was shown to reduce progression of age-related macular
degeneration by 25 percent would be improved by adding omega-3 fatty acids; adding lutein
and zeaxanthin; removing beta-carotene; or reducing zinc. In AREDS2, participants took
one of four AREDS formulations: the original AREDS formulation, AREDS formulation with
no beta-carotene, AREDS with low zinc, AREDS with no beta-carotene and low zinc. In addition,
they took one of four additional supplement or combinations including lutein and zeaxanthin,
omega-3 fatty acids, lutein/zeaxanthin and omega-3 fatty acids, or placebo. The study
reported that there was no overall additional benefit from adding omega-3 fatty acids or
lutein and zeaxanthin to the formulation. However, the study did find benefits in two
subgroups of participants: those not given beta-carotene, and those who had very little
lutein and zeaxanthin in their diets. Removing beta-carotene did not curb the formulation's
protective effect against developing advanced AMD, which was important given that high doses
of beta-carotene had been linked to higher risk of lung cancers in smokers. It was recommended
to replace beta-carotene with lutein and zeaxanthin in future formulations for these reasons.
Cataracts There is also epidemiological evidence that
increasing lutein and zeaxanthin intake lowers the risk of cataract development. Consumption
of more than 2.4 mg of lutein/zeaxanthin daily from foods and supplements was significantly
correlated with reduced incidence of nuclear lens opacities, as revealed from data collected
during a 13- to 15-year period in the Nutrition and Vision Project.
Photophobia A study by Stringham and Hammond, published
in the January/February 2010 issue of Journal of Food Science, discusses the improvement
in visual performance and decrease in light sensitivity in subjects taking 10 mg lutein
and 2 mg zeaxanthin per day. In nutrition
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 6–10 mg/day. The only definitive side effect of excess
lutein consumption is bronzing of the skin. The functional difference between lutein 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 and is extracted from the petals of marigold. It is approved for use in the EU
and Australia and New Zealand but is banned in the USA.
Some foods are considered good sources of the nutrients:
Commercial value The lutein market is segmented into pharmaceutical,
nutraceutical, food, pet foods, and animal 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, skins and as an
antioxidant. It is one of the fastest growing areas of the US$2 billion carotenoid market.
See also List of antioxidants in food
List of phytochemicals in food References
External links Lutein Information Bureau