Lutein

Lutein
Space-filling model of lutein
Names
IUPAC name
β,ε-carotene-3,3'-diol
Other names
Luteine; trans-lutein; 4-​[18-​(4-​Hydroxy-​2,6,6-​trimethyl-​1-​cyclohexenyl)-​3,7,12,16-​tetramethyloctadeca-​1,3,5,7,9,11,13,15,17-​nonaenyl]-​3,5,5-​trimethyl-​cyclohex-​2-​en-​1-​ol
Xanthophyll
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.004.401
E number E161b (colours)
UNII
Properties
C40H56O2
Molar mass 568.871 g/mol
Appearance Red-orange crystalline solid
Melting point 190 °C (374 °F; 463 K)[1]
Insoluble
Solubility in fats Soluble
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Lutein (/ˈluːtiː.ɪn/ or /ˈluːtiːn/;[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.

Lutein is obtained by animals by ingesting plants.[3] In the human retina, lutein and zeaxanthin are absorbed from blood specifically into the macula lutea where they have presumed roles as an antioxidant and for protection against blue light.[4] Lutein is also 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.

Lutein is isomeric with zeaxanthin, differing only in the placement of one double bond. 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.

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][5] 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 is concentrated in the macula, a small area of the retina responsible for three-dimensional vision.[3] Although the precise functional role of retinal lutein has not been proven, its anatomical location in the macula indicates it likely serves to reduce oxidative stress and absorb the high-energy photons of blue light.[4]

Macular degeneration

In 2013, findings of the Age-Related Eye Disease Study showed that a dietary supplement formulation containing lutein reduced progression of age-related macular degeneration (AMD) by 25 percent.[6][7] 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."[7]

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.[6]

Cataract research

There is preliminary epidemiological evidence that increasing lutein and zeaxanthin intake lowers the risk of cataract development.[3][8][9] 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.[10]

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.[11][12] 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.[13]

Bright light sensitivity

A 2016 clinical trial presented evidence for improvement in visual performance and decrease in light sensitivity (glare) in subjects taking 10 mg lutein and 2 mg zeaxanthin per day for 12 months.[14]

In diet

Lutein is a natural part of human diet when orange-yellow fruits and leafy green vegetables are consumed. According to the NHANES 2013-2014 survey, adults in the United States average 1.7 mg/day of lutein and zeaxanthin combined.[15] No recommended dietary allowance currently exists for lutein. Some positive health effects have been seen at dietary intake levels of 6–10 mg/day.[16] The only definitive side effect of excess lutein consumption is bronzing of the skin (carotenodermia).

As a food additive, lutein has the E number E161b (INS number 161b) and is extracted from the petals of African marigold (Tagetes erecta).[17] It is approved for use in the EU[18] and Australia and New Zealand[19] 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. Example: lutein fed to chickens will show up in skin color and egg yolk color.

Some foods contain relatively high amounts of lutein:[3][8][20][21]

Product Lutein/zeaxanthin[3]
(micrograms per 100 grams)
nasturtium (yellow flowers, lutein levels only) 45,000 [21]
kale (raw) 39,550
kale (cooked) 18,246
dandelion leaves (raw) 13,610
nasturtium (leaves, lutein levels only) 13,600 [21]
turnip greens (raw) 12,825
spinach (raw) 12,198
spinach (cooked) 11,308
swiss chard (raw or cooked) 11,000
turnip greens (cooked) 8440
collard greens (cooked) 7694
watercress (raw) 5767
garden peas (raw) 2593
romaine lettuce 2312
zucchini 2125
brussels sprouts 1590
pistachio nuts 1205
broccoli 1121
carrot (cooked) 687
Maize/corn 642
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.[22] 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][22] Neither the U.S. Food and Drug Administration nor the European Food Safety Authority consider lutein an essential nutrient or have 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.

In the dietary supplement industry the major market is for products with claims of helping maintain eye health. 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.[23]

See also

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 "Carotenoids". Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis. July 2016. Retrieved 10 August 2017.
  4. 1 2 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. PMC 4698241 Freely accessible. PMID 26541886. doi:10.1016/j.preteyeres.2015.10.003.
  5. ↑ "Maintaining color stability". Natural Products Insider, Informa Exhibitions, LLC. 1 August 2006. Retrieved 10 August 2017.
  6. 1 2 "NIH study provides clarity on supplements for protection against blinding eye disease". US National Eye Institute, National Institutes of Health, Bethesda, MD. 5 May 2013. Retrieved 10 August 2017.
  7. 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.
  8. 1 2 SanGiovanni JP, Chew EY, Clemons TE (September 2007). "The relationship of dietary carotenoid and vitamin A, E, and C intake with age-related macular degeneration in a case-control study: AREDS Report No. 22". Arch. Ophthalmol. 125 (9): 1225–32. PMID 17846363. doi:10.1001/archopht.125.9.1225.
  9. ↑ 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. PMC 2562026 Freely accessible. PMID 18332316. doi:10.1001/archopht.126.3.354.
  10. ↑ 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. PMID 20590393. doi:10.1185/03007995.2010.494549.
  11. ↑ Liu XH, Yu RB, Liu R, Hao ZX, Han CC, Zhu ZH, Ma L (2014). "Association between lutein and zeaxanthin status and the risk of cataract: a meta-analysis". Nutrients. 6 (1): 452–65. PMC 3916871 Freely accessible. PMID 24451312. doi:10.3390/nu6010452.
  12. ↑ Ma L, Hao ZX, Liu RR, Yu RB, Shi Q, Pan JP (2014). "A dose-response meta-analysis of dietary lutein and zeaxanthin intake in relation to risk of age-related cataract". Graefes Arch. Clin. Exp. Ophthalmol. 252 (1): 63–70. PMID 24150707. doi:10.1007/s00417-013-2492-3.
  13. ↑ Chew EY, SanGiovanni JP, Ferris FL, Wong WT, Agron E, Clemons TE, Sperduto R, Danis R, Chandra SR, Blodi BA, Domalpally A, Elman MJ, Antoszyk AN, Ruby AJ, Orth D, Bressler SB, Fish GE, Hubbard GB, Klein ML, Friberg TR, Rosenfeld PJ, Toth CA, Bernstein P (2013). "Lutein/zeaxanthin for the treatment of age-related cataract: AREDS2 randomized trial report no. 4". JAMA Ophthalmol. 131 (7): 843–50. PMID 23645227. doi:10.1001/jamaophthalmol.2013.4412.
  14. ↑ Stringham JM, O'Brien KJ, Stringham NT (2016). "Macular carotenoid supplementation improves disability glare performance and dynamics of photostress recovery". Eye Vis (Lond). 3: 30. PMC 5106769 Freely accessible. PMID 27857944. doi:10.1186/s40662-016-0060-8.
  15. ↑ NHANES 2013-2014 survey results, reported as What We Eat In America
  16. ↑ Seddon JM, Ajani UA, Sperduto RD (November 1994). "Dietary carotenoids, vitamins A, C, and E, and advanced age-related macular degeneration. Eye Disease Case-Control Study Group". JAMA. 272 (18): 1413–20. PMID 7933422. doi:10.1001/jama.272.18.1413.
  17. ↑ WHO/FAO Codex Alimentarius General Standard for Food Additives
  18. ↑ UK Food Standards Agency: "Current EU approved additives and their E Numbers". Retrieved 2011-10-27.
  19. ↑ Australia New Zealand Food Standards Code."Standard 1.2.4 - Labelling of ingredients". Retrieved 2011-10-27.
  20. ↑ USDA National Nutrient Database for Standard Reference, Release 23 (2010) Archived 2015-03-03 at the Wayback Machine.
  21. 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. ISSN 1750-3841. doi:10.1111/j.1365-2621.2005.tb08336.x.
  22. 1 2 Shao A, Hathcock JN (2006). "Risk assessment for the carotenoids lutein and lycopene". Regulatory Toxicology and Pharmacology : RTP. 45 (3): 289–98. PMID 16814439. doi:10.1016/j.yrtph.2006.05.007. Retrieved 2016-07-17. 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.
  23. ↑ FOD025C The Global Market for Carotenoids, BCC Research
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