Lutein
Encyclopedia
Lutein is a xanthophyll
and one of 600 known naturally occurring carotenoid
s. Lutein is synthesized only by plants and like other xanthophylls is found in high quantities in green leafy vegetables such as spinach
and kale
. In green plants, xanthophylls act to modulate light energy and serve as non-photochemical quenching
agents to deal with triplet chlorophyll (an excited form of 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 to protect the retina from the ionizing effect of blue light.
The principal natural stereoisomer of lutein is (3R,3′R,6′R)-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 (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.
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
(de-esterfication) 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 isomer
ic with zeaxanthin
, differing only in the placement of one double bond.
, 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.
, 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.
(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 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 (AMD). Some studies support the view that supplemental lutein and/or zeaxanthin help protect against AMD.
In 2007, in a 6-year study, 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.
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 (NVP).
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 (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 (INS number 161b) and is extracted from the petals of marigold (Tagetes
erecta). It is approved for use in the EU and Australia and New Zealand however is banned in the USA.
Some foods are considered good sources of the nutrients:
. It is one of the fastest growing areas of the US $2 billion carotenoid market.
Xanthophyll
Xanthophylls are yellow pigments that form one of two major divisions of the carotenoid group. The name is from Greek xanthos + phyllon , due to their formation of the yellow band seen in early chromatography of leaf pigments...
and one of 600 known naturally occurring carotenoid
Carotenoid
Carotenoids are tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some bacteria, and some types of fungus. Carotenoids can be synthesized fats and other basic organic metabolic building...
s. Lutein is synthesized only by plants and like other xanthophylls is found in high quantities in green leafy vegetables such as spinach
Spinach
Spinach is an edible flowering plant in the family of Amaranthaceae. It is native to central and southwestern Asia. It is an annual plant , which grows to a height of up to 30 cm. Spinach may survive over winter in temperate regions...
and kale
Kale
Kale is very high in beta carotene, vitamin K, vitamin C, lutein, zeaxanthin, and reasonably rich in calcium. Kale, as with broccoli and other brassicas, contains sulforaphane , a chemical with potent anti-cancer properties. Boiling decreases the level of sulforaphane; however, steaming,...
. In green plants, xanthophylls act to modulate light energy and serve as non-photochemical quenching
Non-photochemical quenching
Non-photochemical quenching is a mechanism employed by plants and algae to protect themselves from the adverse effects of high light intensity. It involves the quenching of singlet excited state chlorophylls via enhanced internal conversion to the ground state , thus harmlessly dissipating...
agents to deal with triplet chlorophyll (an excited form of 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
Antioxidant
An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...
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
Lutein
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 and kale...
and zeaxanthin
Zeaxanthin
Zeaxanthin is one of the most common carotenoid alcohols found in nature. It is important in the xanthophyll cycle. Synthesized in plants & some micro-organisms, it is the pigment that gives paprika , corn, saffron, and many other plants & microbes their characteristic color.The name is derived...
. The latter predominates at the macula lutea while lutein predominates elsewhere in the retina. There, it may serve to protect the retina from the ionizing effect of blue light.
The principal natural stereoisomer of lutein is (3R,3′R,6′R)-beta,epsilon-carotene-3,3′-diol.
Lutein is a lipophilic
Lipophilic
Lipophilicity, , refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. These non-polar solvents are themselves lipophilic — the axiom that like dissolves like generally holds true...
molecule and is generally insoluble in water. The presence of the long chromophore
Chromophore
A chromophore is the part of a molecule responsible for its color. The color arises when a molecule absorbs certain wavelengths of visible light and transmits or reflects others. The chromophore is a region in the molecule where the energy difference between two different molecular orbitals falls...
of conjugated double bonds (polyene
Polyene
Polyenes are poly-unsaturated organic compounds that contain one or more sequences of alternating double and single carbon-carbon bonds. These double carbon-carbon bonds interact in a process known as conjugation, which results in an overall lower energy state of the molecule.Organic compounds with...
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.
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
Saponification
Saponification is a process that produces soap, usually from fats and lye. In technical terms, saponification involves base hydrolysis of triglycerides, which are esters of fatty acids, to form the sodium salt of a carboxylate. In addition to soap, such traditional saponification processes...
(de-esterfication) 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 isomer
Isomer
In chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...
ic with zeaxanthin
Zeaxanthin
Zeaxanthin is one of the most common carotenoid alcohols found in nature. It is important in the xanthophyll cycle. Synthesized in plants & some micro-organisms, it is the pigment that gives paprika , corn, saffron, and many other plants & microbes their characteristic color.The name is derived...
, differing only in the placement of one double bond.
As a pigment
This xanthophyllXanthophyll
Xanthophylls are yellow pigments that form one of two major divisions of the carotenoid group. The name is from Greek xanthos + phyllon , due to their formation of the yellow band seen in early chromatography of leaf pigments...
, like its sister compound zeaxanthin
Zeaxanthin
Zeaxanthin is one of the most common carotenoid alcohols found in nature. It is important in the xanthophyll cycle. Synthesized in plants & some micro-organisms, it is the pigment that gives paprika , corn, saffron, and many other plants & microbes their characteristic color.The name is derived...
, has primarily been used as a natural colorant due to its orange-red color
Color
Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...
. Lutein absorbs blue
Blue
Blue is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 440–490 nm. It is considered one of the additive primary colours. On the HSV Colour Wheel, the complement of blue is yellow; that is, a colour corresponding to an equal...
light and therefore appears yellow
Yellow
Yellow is the color evoked by light that stimulates both the L and M cone cells of the retina about equally, with no significant stimulation of the S cone cells. Light with a wavelength of 570–590 nm is yellow, as is light with a suitable mixture of red and green...
at low concentrations and orange-red at high concentrations.
Lutein was traditionally used in chicken
Chicken
The chicken is a domesticated fowl, a subspecies of the Red Junglefowl. As one of the most common and widespread domestic animals, and with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird...
feed to provide the yellow color of broiler
Broiler
A broiler is a type of chicken raised specifically for meat production. Modern commercial broilers, typically known as Cornish crosses or Cornish-Rocks are specially bred for large scale, efficient meat production and grow much faster than egg or traditional dual purpose breeds...
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
Egg yolk
An egg yolk is a part of an egg which feeds the developing embryo. The egg yolk is suspended in the egg white by one or two spiral bands of tissue called the chalazae...
. 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 maculaMacula
The macula or macula lutea is an oval-shaped highly pigmented yellow spot near the center of the retina of the human eye. It has a diameter of around 5 mm and is often histologically defined as having two or more layers of ganglion cells...
, 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
Oxidative stress
Oxidative stress represents an imbalance between the production and manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage...
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
Haidinger's brush
Haidinger's brush is an entoptic phenomenon first described by Austrianphysicist Wilhelm Karl von Haidinger in 1844.Many people are able to perceive polarization of light....
, an entoptic phenomenon
Entoptic phenomenon
Entoptic phenomena are visual effects whose source is within the eye itself. In Helmholtz's words:...
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 degenerationMacular degeneration
Age-related macular degeneration is a medical condition which usually affects older adults and results in a loss of vision in the center of the visual field because of damage to the retina. It occurs in “dry” and “wet” forms. It is a major cause of blindness and visual impairment in older adults...
(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 visual function is improved with lutein alone or lutein together with other nutrients and also that more study was needed .
There is epidemiological
Epidemiology
Epidemiology is the study of health-event, health-characteristic, or health-determinant patterns in a population. It is the cornerstone method of public health research, and helps inform policy decisions and evidence-based medicine by identifying risk factors for disease and targets for preventive...
evidence of a relationship between low plasma
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
concentrations of lutein and zeaxanthin, and an increased risk of developing age-related macular degeneration (AMD). Some studies support the view that supplemental lutein and/or zeaxanthin help protect against AMD.
In 2007, in a 6-year study, John Paul SanGiovanni of the National Eye Institute
National Eye Institute
The National Eye Institute is one of the US National Institutes of Health that was established in 1968. The mission of NEI is to prolong and protect the vision of the American people. The NEI conducts and performs research into treating and preventing diseases affecting the eye or vision....
, Maryland
Maryland
Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...
found that lutein and zeaxanthin (nutrients in eggs
Egg (food)
Eggs are laid by females of many different species, including birds, reptiles, amphibians, and fish, and have probably been eaten by mankind for millennia. Bird and reptile eggs consist of a protective eggshell, albumen , and vitellus , contained within various thin membranes...
, spinach
Spinach
Spinach is an edible flowering plant in the family of Amaranthaceae. It is native to central and southwestern Asia. It is an annual plant , which grows to a height of up to 30 cm. Spinach may survive over winter in temperate regions...
and other green vegetables) protect against blindness
Blindness
Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...
(macular degeneration
Macular degeneration
Age-related macular degeneration is a medical condition which usually affects older adults and results in a loss of vision in the center of the visual field because of damage to the retina. It occurs in “dry” and “wet” forms. It is a major cause of blindness and visual impairment in older adults...
), affecting 1.2 million Americans
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, mostly after age 65. Lutein and zeaxanthin reduce the risk of AMD.
Cataracts
There is also epidemiological evidence that increasing lutein and zeaxanthin intake lowers the risk of cataractCataract
A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...
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 (NVP).
Photophobia (abnormal human optical light sensitivity)
A study by Stringham and Hammond, published in the Jan-Feb issue of Journal of Food Science, discusses the improvement in visual performance and decrease in light sensitivity (glare) 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 sublingualSublingual
Sublingual, literally 'under the tongue', from Latin, refers to the pharmacological route of administration by which drugs diffuse into the blood through tissues under the tongue...
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 (carotenodermia).
The functional difference between lutein (free form) and lutein esters is not entirely known. It is suggested that the bioavailability
Bioavailability
In pharmacology, bioavailability is a subcategory of absorption and is used to describe the fraction of an administered dose of unchanged drug that reaches the systemic circulation, one of the principal pharmacokinetic properties of drugs. By definition, when a medication is administered...
is lower for lutein esters, but much debate continues.
As a food additive
Food additive
Food additives are substances added to food to preserve flavor or enhance its taste and appearance.Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines...
, lutein has the E number
E number
E numbers are number codes for food additives that have been assessed for use within the European Union . They are commonly found on food labels throughout the European Union. Safety assessment and approval are the responsibility of the European Food Safety Authority...
E161b (INS number 161b) and is extracted from the petals of marigold (Tagetes
Tagetes
Tagetes is a genus of 56 species of annual and perennial mostly herbaceous plants in the sunflower family . The genus is native to North and South America, but some species have become naturalized around the world. One species, T...
erecta). It is approved for use in the EU and Australia and New Zealand however is banned in the USA.
Some foods are considered good sources of the nutrients:
| Product | Lutein/zeaxanthin (micrograms per hundred grams) |
|---|---|
| kale Kale Kale is very high in beta carotene, vitamin K, vitamin C, lutein, zeaxanthin, and reasonably rich in calcium. Kale, as with broccoli and other brassicas, contains sulforaphane , a chemical with potent anti-cancer properties. Boiling decreases the level of sulforaphane; however, steaming,... (cooked) |
18246 |
| turnip Turnip The turnip or white turnip is a root vegetable commonly grown in temperate climates worldwide for its white, bulbous taproot. Small, tender varieties are grown for human consumption, while larger varieties are grown as feed for livestock... greens (raw) |
12825 |
| spinach Spinach Spinach is an edible flowering plant in the family of Amaranthaceae. It is native to central and southwestern Asia. It is an annual plant , which grows to a height of up to 30 cm. Spinach may survive over winter in temperate regions... (raw) |
12198 |
| spinach Spinach Spinach is an edible flowering plant in the family of Amaranthaceae. It is native to central and southwestern Asia. It is an annual plant , which grows to a height of up to 30 cm. Spinach may survive over winter in temperate regions... (cooked) |
11308 |
| turnip Turnip The turnip or white turnip is a root vegetable commonly grown in temperate climates worldwide for its white, bulbous taproot. Small, tender varieties are grown for human consumption, while larger varieties are grown as feed for livestock... greens (raw) |
8440 |
| collard greens (cooked) | 7694 |
| Watercress Watercress Watercresses are fast-growing, aquatic or semi-aquatic, perennial plants native from Europe to central Asia, and one of the oldest known leaf vegetables consumed by human beings... raw |
5767 |
| garden peas PEAS P.E.A.S. is an acronym in artificial intelligence that stands for Performance, Environment, Actuators, Sensors.-Performance:Performance is a function that measures the quality of the actions the agent did.... |
2593 |
| romaine lettuce Romaine lettuce Romaine or cos lettuce is a variety of lettuce which grows in a tall head of sturdy leaves with a firm rib down the center. Unlike most lettuces, it is tolerant of heat... |
2312 |
| zucchini Zucchini The zucchini is a summer squash which often grows to nearly a meter in length, but which is usually harvested at half that size or less. It is a hybrid of the cucumber. Along with certain other squashes, it belongs to the species Cucurbita pepo. Zucchini can be dark or light green... |
2125 |
| Brussels sprouts | 1590 |
| Pistachio Pistachio The pistachio, Pistacia vera in the Anacardiaceae family, is a small tree originally from Persia , which now can also be found in regions of Syria, Lebanon, Turkey, Greece, Kyrgyzstan, Turkmenistan, India, Pakistan, Egypt, Sicily and possibly Afghanistan , as well as in the United States,... nuts |
1205 |
| broccoli Broccoli Broccoli is a plant in the cabbage family, whose large flower head is used as a vegetable.-General:The word broccoli, from the Italian plural of , refers to "the flowering top of a cabbage".... |
1121 |
| Maize/corn Maize Maize known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable... |
644 |
| egg Egg (food) Eggs are laid by females of many different species, including birds, reptiles, amphibians, and fish, and have probably been eaten by mankind for millennia. Bird and reptile eggs consist of a protective eggshell, albumen , and vitellus , contained within various thin membranes... |
353 |
| carrot Carrot The carrot is a root vegetable, usually orange in colour, though purple, red, white, and yellow varieties exist. It has a crisp texture when fresh... |
256 |
| kiwifruit Kiwifruit The kiwifruit, often shortened to kiwi in many parts of the world, is the edible berry of a cultivar group of the woody vine Actinidia deliciosa and hybrids between this and other species in the genus Actinidia.... |
122 |
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 antioxidantAntioxidant
An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...
. 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
- Lutein-free dietLutein-free dietThe Lutein-free diet is one of several specific diets reported to be beneficial to people with autism spectrum disorders. It is based on the theory of phagocytosis of pigments first described by research nutritionist Sandra Desorgher The Lutein-free diet is also known as 'Sara's Diet' The diet...
(for autism spectrum disorders) - Macular DegenerationMacular degenerationAge-related macular degeneration is a medical condition which usually affects older adults and results in a loss of vision in the center of the visual field because of damage to the retina. It occurs in “dry” and “wet” forms. It is a major cause of blindness and visual impairment in older adults...
- ZeaxanthinZeaxanthinZeaxanthin is one of the most common carotenoid alcohols found in nature. It is important in the xanthophyll cycle. Synthesized in plants & some micro-organisms, it is the pigment that gives paprika , corn, saffron, and many other plants & microbes their characteristic color.The name is derived...