Lutein

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Contents

Lutein
Luteine - Lutein.svg
Lutein molecule spacefill.png
Names
IUPAC name
(3R,6R,3′R)-β,ε-Carotene-3,3′-diol
Systematic IUPAC name
(1R,4R)-4-{(1E,3E,5E,7E,9E,11E,13E,15E,17E)-18-[(4R)-4-Hydroxy-2,6,6-trimethylcyclohex-1-en-1-yl]-3,7,12,16-tetramethyloctadeca-1,3,5,7,9,11,13,15,17-nonaen-1-yl}-3,5,5-trimethylcyclohex-2-en-1-ol
Other names
  • Luteine
  • trans-Lutein
  • Xanthophyll
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.004.401 OOjs UI icon edit-ltr-progressive.svg
E number E161b (colours)
PubChem CID
UNII
  • InChI=1S/C40H56O2/c1-29(17-13-19-31(3)21-23-37-33(5)25-35(41)27-39(37,7)8)15-11-12-16-30(2)18-14-20-32(4)22-24-38-34(6)26-36(42)28-40(38,9)10/h11-25,35-37,41-42H,26-28H2,1-10H3/b12-11+,17-13+,18-14+,23-21+,24-22+,29-15+,30-16+,31-19+,32-20+/t35-,36+,37-/m0/s1 Yes check.svgY
    Key: KBPHJBAIARWVSC-RGZFRNHPSA-N Yes check.svgY
  • InChI=1S/C40H56O2/c1-29(17-13-19-31(3)21-23-37-33(5)25-35(41)27-39(37,7)8)15-11-12-16-30(2)18-14-20-32(4)22-24-38-34(6)26-36(42)28-40(38,9)10/h11-25,35-37,41-42H,26-28H2,1-10H3/b12-11+,17-13+,18-14+,23-21+,24-22+,29-15+,30-16+,31-19+,32-20+/t35-,36+,37-/m0/s1
    Key: KBPHJBAIARWVSC-RGZFRNHPBY
  • Key: KBPHJBAIARWVSC-RGZFRNHPSA-N
  • CC1=C(C(C[C@@H](C1)O)(C)C)/C=C/C(=C/C=C/C(=C/C=C/C=C(\C)/C=C/C=C(\C)/C=C/[C@H]2C(=C[C@@H](CC2(C)C)O)C)/C)/C
Properties
C40H56O2
Molar mass 568.871 g/mol
AppearanceRed-orange crystalline solid
Melting point 190 °C (374 °F; 463 K) [1]
Insoluble
Solubility in fatsSoluble
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Lutein ( /ˈljuːtiɪn,-tiːn/ ; [2] from Latin luteus meaning "yellow") 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, an excited form of chlorophyll which is overproduced at very high light levels during photosynthesis. See xanthophyll cycle for this topic.

Animals obtain lutein by ingesting plants. [3] In the human retina, lutein is absorbed from blood specifically into the macula lutea, [4] although its precise role in the body is unknown. [3] Lutein is also found in egg yolks and animal fats.

Lutein is isomeric with zeaxanthin, differing only in the placement of one double bond. Lutein and zeaxanthin can be interconverted in the body through an intermediate called meso-zeaxanthin. [5] 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-esterification) 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.

As a pigment

This xanthophyll, like its sister compound zeaxanthin, has primarily been used in food and supplement manufacturing as a colorant due to its yellow-red color. [3] [6] Lutein absorbs blue light and therefore appears yellow at low concentrations and orange-red at high concentrations.

Many songbirds (like golden oriole, evening grosbeak, yellow warbler, common yellowthroat and Javan green magpies, but not American goldfinch or yellow canaries [7] ) deposit lutein obtained from the diet into growing tissues to color their feathers. [8] [9]

Role in human eyes

Although lutein is concentrated in the macula – a small area of the retina responsible for three-color vision – the precise functional role of retinal lutein has not been determined. [3]

Macular degeneration

In 2013, findings of the Age-Related Eye Disease Study (AREDS2) showed that a dietary supplement formulation containing lutein reduced progression of age-related macular degeneration (AMD) by 25 percent. [10] [11] However, lutein and zeaxanthin had no overall effect on preventing AMD, but rather "the participants with low dietary intake of lutein and zeaxanthin at the start of the study, but who took an AREDS formulation with lutein and zeaxanthin during the study, were about 25 percent less likely to develop advanced AMD compared with participants with similar dietary intake who did not take lutein and zeaxanthin." [11]

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 (10 mg and 2 mg), omega-3 fatty acids (1,000 mg), 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 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. [10]

Cataract research

There is preliminary epidemiological evidence that increasing lutein and zeaxanthin intake lowers the risk of cataract development. [3] [17] [18] 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 one study. [19]

Two meta-analyses confirm a correlation between high diet content or high serum concentrations of lutein and zeaxanthin and a decrease in the risk of cataract. [20] [21] There is only one published clinical intervention trial testing for an effect of lutein and zeaxanthin supplementation on cataracts. The AREDS2 trial enrolled subjects at risk for progression to advanced age-related macular degeneration. Overall, the group getting lutein (10 mg) and zeaxanthin (2 mg) were NOT less likely to progress to needing cataract surgery. The authors speculated that there may be a cataract prevention benefit for people with low dietary intake of lutein and zeaxanthin, but recommended more research. [22]

In diet

Lutein is a natural part of a human diet found in orange-yellow fruits and flowers, and in leafy vegetables. According to the NHANES 2013-2014 survey, adults in the United States consume on average 1.7 mg/day of lutein and zeaxanthin combined. [23] No recommended dietary allowance currently exists for lutein. Some positive health effects have been seen at dietary intake levels of 6–10 mg/day. [24] The only definitive side effect of excess lutein consumption is bronzing of the skin (carotenodermia).[ citation needed ]

As a food additive, lutein has the E number E161b (INS number 161b) and is extracted from the petals of African marigold ( Tagetes erecta ). [25] It is approved for use in the EU [26] and Australia and New Zealand. [27] In the United States lutein may not be used as a food coloring for foods intended for human consumption, but can be added to animal feed and is allowed as a human dietary supplement often in combination with zeaxanthin. Example: lutein fed to chickens will show up in skin color and egg yolk color. [28] [29]

Some foods contain relatively high amounts of lutein: [3] [17] [30] [31] [32] [33]

ProductLutein + zeaxanthin [3]
(micrograms per 100 grams)
nasturtium (yellow flowers, lutein levels only)45,000 [31]
pot marigold (yellow and orange flowers, lutein levels only)29,800
kale (raw)39,550
kale (cooked)18,246
dandelion leaves (raw)13,610
nasturtium (leaves, lutein levels only)13,600 [31]
turnip greens (raw)12,825
spinach (raw)12,198
spinach (cooked)11,308
swiss chard (raw or cooked)11,000
turnip greens (cooked)8,440
collard greens (cooked)7,694
watercress (raw)5,767
garden peas (raw)2,593
romaine lettuce 2,312
zucchini (courgettes)2,125
brussels sprouts 1,590
broccoli, raw1,403
pistachio nuts1,205
broccoli, cooked1,121
carrot (cooked)687
maize/corn642
egg (hard boiled)353
avocado (raw)271
carrot (raw)256
kiwifruit 122

Safety

In humans, the Observed Safe Level (OSL) for lutein, based on a non-government organization evaluation, is 20 mg/day. [34] Although much higher levels have been tested without adverse effects and may also be safe, the data for intakes above the OSL are not sufficient for a confident conclusion of long-term safety. [3] [34] Neither the U.S. Food and Drug Administration nor the European Food Safety Authority considers lutein an essential nutrient or has acted to set a tolerable upper intake level. [3]

Commercial value

The lutein market is segmented into pharmaceutical, dietary supplement, food, pet food, and animal and fish feed. The pharmaceutical market for lutein is estimated to be about US$190 million, and the nutraceutical and food categories are estimated to be about US$110 million. Pet food and other animal applications for lutein are estimated at US$175 million annually. This includes chickens (usually in combination with other carotenoids), to get color in egg yolks, and fish farms to color the flesh closer to wild-caught color. [35] In the dietary supplement industry, the major market for lutein is for products with claims of helping maintain eye health. [36] Newer applications are emerging in oral and topical products for skin health. Skin health via orally consumed supplements is one of the fastest growing areas of the US$2 billion carotenoid market. [37]

See also

Related Research Articles

<span class="mw-page-title-main">Carotene</span> Class of compounds

The term carotene (also carotin, from the Latin carota, "carrot") is used for many related unsaturated hydrocarbon substances having the formula C40Hx, which are synthesized by plants but in general cannot be made by animals (with the exception of some aphids and spider mites which acquired the synthesizing genes from fungi). Carotenes are photosynthetic pigments important for photosynthesis. Carotenes contain no oxygen atoms. They absorb ultraviolet, violet, and blue light and scatter orange or red light, and (in low concentrations) yellow light.

<span class="mw-page-title-main">Lycopene</span> Carotenoid pigment

Lycopene is an organic compound classified as a tetraterpene and a carotene. Lycopene is a bright red carotenoid hydrocarbon found in tomatoes and other red fruits and vegetables.

Tocopherols are a class of organic compounds comprising various methylated phenols, many of which have vitamin E activity. Because the vitamin activity was first identified in 1936 from a dietary fertility factor in rats, it was named tocopherol, from Greek τόκοςtókos 'birth' and φέρεινphérein 'to bear or carry', that is 'to carry a pregnancy', with the ending -ol signifying its status as a chemical alcohol.

<span class="mw-page-title-main">Vitamin A</span> Essential nutrient

Vitamin A is a fat-soluble vitamin and an essential nutrient for animals. The term "vitamin A" encompasses a group of chemically related organic compounds that includes retinol, retinal, retinoic acid, and several provitamin (precursor) carotenoids, most notably beta-carotene. Vitamin A has multiple functions: it is essential for embryo development and growth, for maintenance of the immune system, and for vision, where it combines with the protein opsin to form rhodopsin – the light-absorbing molecule necessary for both low-light and color vision.

<span class="mw-page-title-main">Macula</span> Oval-shaped pigmented area near the center of the retina

The macula (/ˈmakjʊlə/) or macula lutea is an oval-shaped pigmented area in the center of the retina of the human eye and in other animals. The macula in humans has a diameter of around 5.5 mm (0.22 in) and is subdivided into the umbo, foveola, foveal avascular zone, fovea, parafovea, and perifovea areas.

<span class="mw-page-title-main">Carotenoid</span> Class of chemical compounds; yellow, orange or red plant pigments

Carotenoids are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, corn, tomatoes, canaries, flamingos, salmon, lobster, shrimp, and daffodils. Over 1,100 identified carotenoids can be further categorized into two classes – xanthophylls and carotenes.

The National Eye Institute (NEI) is part of the U.S. National Institutes of Health (NIH), an agency of the U.S. Department of Health and Human Services. The mission of NEI is "to eliminate vision loss and improve quality of life through vision research." NEI consists of two major branches for research: an extramural branch that funds studies outside NIH and an intramural branch that funds research on the NIH campus in Bethesda, Maryland. Most of the NEI budget funds extramural research.

<span class="mw-page-title-main">Yolk</span> Part of an egg which feeds the developing embryo

Among animals which produce eggs, the yolk is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example because they are laid in situations where the food supply is sufficient or because the embryo develops in the parent's body, which supplies the food, usually through a placenta. Reproductive systems in which the mother's body supplies the embryo directly are said to be matrotrophic; those in which the embryo is supplied by yolk are said to be lecithotrophic. In many species, such as all birds, and most reptiles and insects, the yolk takes the form of a special storage organ constructed in the reproductive tract of the mother. In many other animals, especially very small species such as some fish and invertebrates, the yolk material is not in a special organ, but inside the egg cell.

β-Carotene Red-orange pigment of the terpenoids class

β-Carotene (beta-carotene) is an organic, strongly colored red-orange pigment abundant in fungi, plants, and fruits. It is a member of the carotenes, which are terpenoids (isoprenoids), synthesized biochemically from eight isoprene units and thus having 40 carbons.

<span class="mw-page-title-main">Xanthophyll</span> Chemical compounds subclass

Xanthophylls are yellow pigments that occur widely in nature and form one of two major divisions of the carotenoid group; the other division is formed by the carotenes. The name is from Greek: xanthos (ξανθός), meaning "yellow", and phyllon (φύλλον), meaning "leaf"), due to their formation of the yellow band seen in early chromatography of leaf pigments.

<span class="mw-page-title-main">Multivitamin</span> Dietary supplement containing vitamins

A multivitamin is a preparation intended to serve as a dietary supplement with vitamins, dietary minerals, and other nutritional elements. Such preparations are available in the form of tablets, capsules, pastilles, powders, liquids, or injectable formulations. Other than injectable formulations, which are only available and administered under medical supervision, multivitamins are recognized by the Codex Alimentarius Commission as a category of food.

<span class="mw-page-title-main">Macular degeneration</span> Medical condition associated with vision loss

Macular degeneration, also known as age-related macular degeneration, is a medical condition which may result in blurred or no vision in the center of the visual field. Early on there are often no symptoms. Over time, however, some people experience a gradual worsening of vision that may affect one or both eyes. While it does not result in complete blindness, loss of central vision can make it hard to recognize faces, drive, read, or perform other activities of daily life. Visual hallucinations may also occur.

<span class="mw-page-title-main">Astaxanthin</span> Chemical compound

Astaxanthin is a keto-carotenoid within a group of chemical compounds known as terpenes. Astaxanthin is a metabolite of zeaxanthin and canthaxanthin, containing both hydroxyl and ketone functional groups. It is a lipid-soluble pigment with red coloring properties, which result from the extended chain of conjugated double bonds at the center of the compound. The presence of the hydroxyl functional groups and the hydrophobic hydrocarbons render the molecule amphiphilic.

The Age-Related Eye Disease Study (AREDS) was a clinical trial sponsored by the National Eye Institute that ran from 1992 to 2001. The study was designed to:

<span class="mw-page-title-main">Cone dystrophy</span> Medical condition

A cone dystrophy is an inherited ocular disorder characterized by the loss of cone cells, the photoreceptors responsible for both central and color vision.

<span class="mw-page-title-main">Zeaxanthin</span> Chemical compound

Zeaxanthin is one of the most common carotenoids in nature, and is used in the xanthophyll cycle. Synthesized in plants and some micro-organisms, it is the pigment that gives paprika, corn, saffron, goji (wolfberries), and many other plants and microbes their characteristic color.

<span class="mw-page-title-main">Carotenosis</span> Skin discoloration caused by carotenoids

Carotenosis is a benign and reversible medical condition where an excess of dietary carotenoids results in orange discoloration of the outermost skin layer. The discoloration is most easily observed in light-skinned people and may be mistaken for jaundice. Carotenoids are lipid-soluble compounds that include alpha- and beta-carotene, beta-cryptoxanthin, lycopene, lutein, and zeaxanthin. The primary serum carotenoids are beta-carotene, lycopene, and lutein. Serum levels of carotenoids vary between region, ethnicity, and sex in the healthy population. All are absorbed by passive diffusion from the gastrointestinal tract and are then partially metabolized in the intestinal mucosa and liver to vitamin A. From there they are transported in the plasma into the peripheral tissues. Carotenoids are eliminated via sweat, sebum, urine, and gastrointestinal secretions. Carotenoids contribute to normal-appearing human skin color, and are a significant component of physiologic ultraviolet photoprotection.

Capsanthin is a natural red dye of the xanthophyll class of carotenoids. As a food coloring, it has the E number E160c(i). Capsanthin is the main carotenoid in the Capsicum annuum species of plants including red bell pepper, New Mexico chile, and cayenne peppers and a component of paprika oleoresin. Capsanthin is also found in some species of lily. Among other carotenoids, capsanthin is considered to have the greatest antioxidant capacity due to the presence of eleven conjugated double bonds, a conjugated keto group, and a cyclopentane ring.

<i>meso</i>-Zeaxanthin Xanthophyll carotenoid

meso-Zeaxanthin (3R,3´S-Zeaxanthin) is a xanthophyll carotenoid and is one of the three stereoisomers of zeaxanthin. Of the three stereoisomers, meso-zeaxanthin is the second most abundant in nature after 3R,3´R-zeaxanthin, which is produced by plants and algae. meso-Zeaxanthin has been identified in specific tissues of marine organisms and in the macula lutea, also known as the "yellow spot", of the human retina.

<span class="mw-page-title-main">Emily Chew</span> American ophthalmologist

Emily Ying Chew is an American ophthalmologist and an expert on the human retina with a strong clinical and research interest in diabetic eye disease and age-related eye diseases. She currently works for the National Eye Institute (NEI) at the National Institutes of Health (NIH) in Bethesda, Maryland, where she serves as deputy director of the Division of Epidemiology and Clinical Applications (DECA) and the Institute's deputy clinical director. She designs and implements Phase 1, 2 and 3 clinical trials at the NIH Clinical Center. Chew is board certified in ophthalmology.

References

  1. ↑ MSDS at Carl Roth (Lutein Rotichrom, German).
  2. ↑ "Lutein", Random House Webster's Unabridged Dictionary.
  3. 1 2 3 4 5 6 7 8 9 "Carotenoids". Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis. July 2016. Retrieved 10 August 2017.
  4. ↑ Bernstein, P. S.; Li, B; Vachali, P. P.; Gorusupudi, A; Shyam, R; Henriksen, B. S.; Nolan, J. M. (2015). "Lutein, Zeaxanthin, and meso-Zeaxanthin: The Basic and Clinical Science Underlying Carotenoid-based Nutritional Interventions against Ocular Disease". Progress in Retinal and Eye Research. 50: 34–66. doi:10.1016/j.preteyeres.2015.10.003. PMC   4698241 . PMID   26541886.
  5. ↑ Krinksy, Norman; Landrum, John; Bone, Richard (2003). "Biological Mechanisms of the Protective Role of Lutein and Zeaxanthin in the Eye". Annual Review of Nutrition. 23 (1): 171–201. doi:10.1146/annurev.nutr.23.011702.073307. PMID   12626691.
  6. ↑ "Maintaining color stability". Natural Products Insider, Informa Exhibitions, LLC. 1 August 2006. Archived from the original on 10 August 2017. Retrieved 10 August 2017.
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  8. ↑ McGraw KJ, Beebee MD, Hill GE, Parker RS (August 2003). "Lutein-based plumage coloration in songbirds is a consequence of selective pigment incorporation into feathers". Comparative Biochemistry and Physiology. Part B, Biochemistry & Molecular Biology. 135 (4): 689–96. doi:10.1016/S1096-4959(03)00164-7. PMID   12892761.
  9. ↑ Gill, Victoria. "Sold for a song: The forest birds captured for their tuneful voices". BBC News. Retrieved 31 December 2017.
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  11. 1 2 "The AREDS Formulation and Age-Related Macular Degeneration". US National Eye Institute, National Institutes of Health, Bethesda, MD. November 2011. Retrieved 10 August 2017.
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  13. ↑ Wang X, Jiang C, Zhang Y, et al. (2014). "Role of lutein supplementation in the management of age-related macular degeneration: meta-analysis of randomized controlled trials". Ophthalmic Res. 52 (4): 198–205. doi:10.1159/000363327. PMID   25358528. S2CID   5055854.
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  15. 1 2 Evans, Jennifer R.; Lawrenson, John G. (13 September 2023). "Antioxidant vitamin and mineral supplements for slowing the progression of age-related macular degeneration". The Cochrane Database of Systematic Reviews. 2023 (9): CD000254. doi:10.1002/14651858.CD000254.pub5. ISSN   1469-493X. PMC  10498493. PMID   37702300.
  16. ↑ "Lutein + Zeaxanthin Content of Selected Foods". Linus Pauling Institute, Oregon State University, Corvallis. 2014. Retrieved 20 May 2014.
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  18. ↑ Moeller SM, Voland R, Tinker L, Blodi BA, Klein ML, Gehrs KM, Johnson EJ, Snodderly DM, Wallace RB, Chappell RJ, Parekh N, Ritenbaugh C, Mares JA (2008). "Associations between age-related nuclear cataract and lutein and zeaxanthin in the diet and serum in the Carotenoids in the Age-Related Eye Disease Study, an Ancillary Study of the Women's Health Initiative". Arch Ophthalmol. 126 (3): 354–64. doi:10.1001/archopht.126.3.354. PMC   2562026 . PMID   18332316.
  19. ↑ Barker Fm, 2nd (2010). "Dietary supplementation: effects on visual performance and occurrence of AMD and cataracts". Current Medical Research and Opinion. 26 (8): 2011–23. doi:10.1185/03007995.2010.494549. PMID   20590393. S2CID   206965363.{{cite journal}}: CS1 maint: numeric names: authors list (link)
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  23. ↑ NHANES 2013-2014 survey results, reported as What We Eat In America
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  25. ↑ WHO/FAO Codex Alimentarius General Standard for Food Additives
  26. ↑ UK Food Standards Agency: "Current EU approved additives and their E Numbers" . Retrieved 27 October 2011.
  27. ↑ Australia New Zealand Food Standards Code. "Standard 1.2.4 - Labelling of ingredients" . Retrieved 27 October 2011.
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  29. ↑ Lokaewmanee, Kanda; Yamauchi, Koh-en; Komori, Tsutomu; Saito, Keiko (2011). "Enhancement of Yolk Color in Raw and Boiled Egg Yolk with Lutein from Marigold Flower Meal and Marigold Flower Extract". Journal of Poultry Science. 48 (1): 25–32. doi: 10.2141/jpsa.010059 . ISSN   1346-7395 . Retrieved 21 February 2020.
  30. ↑ USDA National Nutrient Database for Standard Reference, Release 23 (2010) Archived 3 March 2015 at the Wayback Machine
  31. 1 2 3 Niizu, P.Y.; Delia B. Rodriguez-Amaya (2005). "Flowers and Leaves of Tropaeolum majus L. as Rich Sources of Lutein". Journal of Food Science. 70 (9): S605–S609. doi:10.1111/j.1365-2621.2005.tb08336.x. ISSN   1750-3841.
  32. ↑ Eisenhauer, Bronwyn; Natoli, Sharon; Liew, Gerald; Flood, Victoria M. (9 February 2017). "Lutein and Zeaxanthin—Food Sources, Bioavailability and Dietary Variety in Age-Related Macular Degeneration Protection". Nutrients. 9 (2): 120. doi: 10.3390/nu9020120 . PMC   5331551 . PMID   28208784.
  33. ↑ Manke Natchigal, A.; Oliveira Stringheta, A.C.; Corrêa Bertoldi, M.; Stringheta, P.C. (2012). "QUANTIFICATION AND CHARACTERIZATION OF LUTEIN FROM TAGETES (TAGETES PATULA L.) AND CALENDULA (CALENDULA OFFICINALIS L.) FLOWERS". Acta Hortic. 939, 309–314. Archived from the original on 14 May 2021. Retrieved 3 July 2019.
  34. 1 2 Shao A, Hathcock JN (2006). "Risk assessment for the carotenoids lutein and lycopene". Regulatory Toxicology and Pharmacology. 45 (3): 289–98. doi:10.1016/j.yrtph.2006.05.007. PMID   16814439. The OSL risk assessment method indicates that the evidence of safety is strong at intakes up to 20mg/d for lutein, and 75 mg/d for lycopene, and these levels are identified as the respective OSLs. Although much higher levels have been tested without adverse effects and may be safe, the data for intakes above these levels are not sufficient for a confident conclusion of long-term safety.
  35. ↑ Lokaewmanee, Kanda & Yamauchi (2011). "Enhancement of Yolk Color in Raw and Boiled Egg Yolk with Lutein from Marigold Flower Meal and Marigold Flower Extract". The Journal of Poultry Science. 48: 25–32. doi: 10.2141/jpsa.010059 – via ResearchGate.
  36. ↑ Campbell, J. (14 January 2021). "Natural Eye Supplements Care For Your Long-Term Vision". Intechra Health. Retrieved 16 January 2021.
  37. ↑ FOD025C The Global Market for Carotenoids, BCC Research
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