Β-Carotene: Difference between revisions

β-Carotene
	; Skeletal formula
	; Ball-and-stick model
	; Space-filling model
Names
	IUPAC name β,β-Carotene
	Systematic IUPAC name 1,1′-[(1E,3E,5E,7E,9E,11E,13E,15E,17E)-3,7,12,16-Tetramethyloctadeca-1,3,5,7,9,11,13,15,17-nonaene-1,18-diyl]bis(2,6,6-trimethylcyclohex-1-ene)
	Other names Betacarotene (INN), β-Carotene, Food Orange 5, Provitamin A
Identifiers
CAS Number	7235-40-7 ;
3D model (JSmol)	Interactive image;
3DMet	B00389;
Beilstein Reference	1917416
ChEBI	CHEBI:17579 ;
ChEMBL	ChEMBL1293 ;
ChemSpider	4444129 ;
ECHA InfoCard	100.027.851
EC Number	230-636-6;
E number	E160a (colours)
KEGG	C02094;
PubChem CID	5280489;
UNII	01YAE03M7J ;
CompTox Dashboard (EPA)	DTXSID3020253 ;
	InChI InChI=1S/C40H56/c1-31(19-13-21-33(3)25-27-37-35(5)23-15-29-39(37,7)8) 17-11-12-18-32(2)20-14-22-34(4)26-28-38-36(6)24-16-30-40(38,9) 10/h11-14,17-22,25-28H,15-16,23-24,29-30H2,1-10H3 Key: OENHQHLEOONYIE-UHFFFAOYSA-N ;
	SMILES CC2(C)CCCC(\C)=C2\C=C\C(\C)=C\C=C\C(\C)=C\C=C\C=C(/C)\C=C\C=C(/C)\C=C\C1=C(/C)CCCC1(C)C;
Properties
Chemical formula	C40H56
Molar mass	536.888 g·mol−1
Appearance	Dark orange crystals
Density	1.00 g/cm3
Melting point	183 °C (361 °F; 456 K) ; decomposes
Boiling point	654.7 °C (1,210.5 °F; 927.9 K) ; at 760 mmHg (101324 Pa)
Solubility in water	Insoluble
Solubility	Soluble in CS2, benzene, CHCl3, ethanol; Insoluble in glycerin
Solubility in dichloromethane	4.51 g/kg (20 °C) = 5.98 g/L (given BCM density of 1.3266 g/cm3 at 20°C)
Solubility in hexane	0.1 g/L
log P	14.764
Vapor pressure	2.71·10−16 mmHg
Refractive index (nD)	1.565
Pharmacology
ATC code	A11CA02 (WHO) D02BB01 (WHO)
Hazards
	GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H315, H319, H412
Precautionary statements	P264, P273, P280, P302+P352, P305+P351+P338, P321, P332+P313, P337+P313, P362, P501
NFPA 704 (fire diamond)	0 1 0
Flash point	103 °C (217 °F; 376 K)
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

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β-Carotene (beta-carotene) is an organic, strongly colored red-orange pigment abundant in fungi,^[7] 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.

Dietary β-carotene is a provitamin A compound, converting in the body to retinol (vitamin A).^[8] In foods, it has rich content in carrots, pumpkin, spinach, and sweet potato.^[8] It is used as a dietary supplement and may be prescribed to treat erythropoietic protoporphyria, an inherited condition of sunlight sensitivity.^[9]

β-carotene is the most common carotenoid in plants.^[8] When used as a food coloring, it has the E number E160a.^[10]^: 119 The structure was deduced in 1930.^[11]

Isolation of β-carotene from fruits abundant in carotenoids is commonly done using column chromatography. It is industrially extracted from richer sources such as the algae Dunaliella salina.^[12] The separation of β-carotene from the mixture of other carotenoids is based on the polarity of a compound. β-Carotene is a non-polar compound, so it is separated with a non-polar solvent such as hexane.^[13] Being highly conjugated, it is deeply colored, and as a hydrocarbon lacking functional groups, it is lipophilic.

Provitamin A activity

Plant carotenoids are the primary dietary source of provitamin A worldwide, with β-carotene as the best-known provitamin A carotenoid.^[8] Others include α-carotene and β-cryptoxanthin.^[8] Carotenoid absorption is restricted to the duodenum of the small intestine. One molecule of β-carotene can be cleaved by the intestinal enzyme β,β-carotene 15,15'-monooxygenase into two molecules of vitamin A.^[8]^[14]^[15]

Absorption, metabolism and excretion

As part of the digestive process, food-sourced carotenoids must be separated from plant cells and incorporated into lipid-containing micelles to be bioaccessible to intestinal enterocytes.^[8] If already extracted (or synthetic) and then presented in an oil-filled dietary supplement capsule, there is greater bioavailability compared to that from foods.^[16]

At the enterocyte cell wall, β-carotene is taken up by the membrane transporter protein scavenger receptor class B, type 1 (SCARB1). Absorbed β-carotene is then either incorporated as such into chylomicrons or first converted to retinal and then retinol, bound to retinol binding protein 2, before being incorporated into chylomicrons.^[8] The conversion process consists of one molecule of β-carotene cleaved by the enzyme beta-carotene 15,15'-dioxygenase, which is encoded by the BCO1 gene, into two molecules of retinal.^[8] When plasma retinol is in the normal range the gene expression for SCARB1 and BCO1 are suppressed, creating a feedback loop that suppresses β-carotene absorption and conversion.^[16]

The majority of chylomicrons are taken up by the liver, then secreted into the blood repackaged into low density lipoproteins (LDLs).^[8] From these circulating lipoproteins and the chylomicrons that bypassed the liver, β-carotene is taken into cells via receptor SCARB1. Human tissues differ in expression of SCARB1, and hence β-carotene content. Examples expressed as ng/g, wet weight: liver=479, lung=226, prostate=163 and skin=26.^[16]

Once taken up by peripheral tissue cells, the major usage of absorbed β-carotene is as a precursor to retinal via symmetric cleavage by the enzyme beta-carotene 15,15'-dioxygenase, which is encoded by the BCO1 gene.^[8] A lesser amount is metabolized by the mitochondrial enzyme beta-carotene 9',10'-dioxygenase, which is encoded by the BCO2 gene. The products of this asymmetric cleavage are two beta-ionone molecules and rosafluene. BCO2 appears to be involved in preventing excessive accumulation of carotenoids; a BCO2 defect in chickens results in yellow skin color due to accumulation in subcutaneous fat.^[17]^[18]

Conversion factors

For counting dietary vitamin A intake, β-carotene may be converted either using the newer retinol activity equivalents (RAE) or the older international unit (IU).^[8]

Retinol activity equivalents (RAEs)

Since 2001, the US Institute of Medicine uses retinol activity equivalents (RAE) for their Dietary Reference Intakes, defined as follows:^[8]^[19]

1 μg RAE = 1 μg retinol from food or supplements
1 μg RAE = 2 μg all-trans-β-carotene from supplements
1 μg RAE = 12 μg of all-trans-β-carotene from food
1 μg RAE = 24 μg α-carotene or β-cryptoxanthin from food

RAE takes into account carotenoids' variable absorption and conversion to vitamin A by humans better than and replaces the older retinol equivalent (RE) (1 μg RE = 1 μg retinol, 6 μg β-carotene, or 12 μg α-carotene or β-cryptoxanthin).^[19] RE was developed 1967 by the United Nations/World Health Organization Food and Agriculture Organization (FAO/WHO).^[20]

International Units

Another older unit of vitamin A activity is the international unit (IU).^[8] Like retinol equivalent, the international unit does not take into account carotenoid variable absorption and conversion to vitamin A by humans, as well as the more modern retinol activity equivalent. Unfortunately, food and supplement labels still generally use IU, but IU can be converted to the more useful retinol activity equivalent as follows:^[19]

1 μg RAE = 3.33 IU retinol
1 IU retinol = 0.3 μg RAE
1 IU β-carotene from supplements = 0.3 μg RAE
1 IU β-carotene from food = 0.05 μg RAE
1 IU α-carotene or β-cryptoxanthin from food = 0.025 μg RAE1

Dietary sources

The average daily intake of β-carotene is in the range 2–7 mg, as estimated from a pooled analysis of 500,000 women living in the US, Canada, and some European countries.^[21] Beta-carotene is found in many foods and is sold as a dietary supplement.^[8] β-Carotene contributes to the orange color of many different fruits and vegetables. Vietnamese gac (Momordica cochinchinensis Spreng.) and crude palm oil are particularly rich sources, as are yellow and orange fruits, such as cantaloupe, mangoes, pumpkin, and papayas, and orange root vegetables such as carrots and sweet potatoes.^[8]

The color of β-carotene is masked by chlorophyll in green leaf vegetables such as spinach, kale, sweet potato leaves, and sweet gourd leaves.^[8]^[22]

The U.S. Department of Agriculture lists foods high in β-carotene content:^[23]

Food	Beta-carotene Milligrams per 100 g
Sweet potato, skinned, boiled	9.4
Carrot juice	9.3
Carrots, raw or boiled	9.2
Kale, boiled	8.8
Pumpkin, canned	6.9
Spinach, canned	5.9

No dietary requirement

Government and non-government organizations have not set a dietary requirement for β-carotene.^[16]

Side effects

Excess β-carotene is predominantly stored in the fat tissues of the body.^[8] The most common side effect of excessive β-carotene consumption is carotenodermia, a physically harmless condition that presents as a conspicuous orange skin tint arising from deposition of the carotenoid in the outermost layer of the epidermis.^[8]^[9]^[16]^[24]

Carotenosis

Carotenoderma, also referred to as carotenemia, is a benign and reversible medical condition where an excess of dietary carotenoids results in orange discoloration of the outermost skin layer.^[8] It is associated with a high blood β-carotene value. This can occur after a month or two of consumption of beta-carotene rich foods, such as carrots, carrot juice, tangerine juice, mangos, or in Africa, red palm oil. β-carotene dietary supplements can have the same effect. The discoloration extends to palms and soles of feet, but not to the white of the eye, which helps distinguish the condition from jaundice. Carotenodermia is reversible upon cessation of excessive intake.^[25] Consumption of greater than 30 mg/day for a prolonged period has been confirmed as leading to carotenemia.^[16]^[26]

No risk for hypervitaminosis A

At the enterocyte cell wall, β-carotene is taken up by the membrane transporter protein scavenger receptor class B, type 1 (SCARB1). Absorbed β-carotene is then either incorporated as such into chylomicrons or first converted to retinal and then retinol, bound to retinol binding protein 2, before being incorporated into chylomicrons. The conversion process consists of one molecule of β-carotene cleaved by the enzyme beta-carotene 15,15'-dioxygenase, which is encoded by the BCO1 gene, into two molecules of retinal. When plasma retinol is in the normal range the gene expression for SCARB1 and BCO1 are suppressed, creating a feedback loop that suppresses absorption and conversion. Because of these two mechanisms, high intake will not lead to hypervitaminosis A.^[16]

Drug interactions

β-Carotene can interact with medication used for lowering cholesterol.^[8] Taking them together can lower the effectiveness of these medications and is considered only a moderate interaction.^[8] Bile acid sequestrants and proton-pump inhibitors can decrease absorption of β-carotene.^[27] Consuming alcohol with β-carotene can decrease its ability to convert to retinol and could possibly result in hepatotoxicity.^[28]

β-Carotene and lung cancer in smokers

Chronic high doses of β-carotene supplementation increases the probability of lung cancer in smokers^[8]^[29] while its natural vitamer, retinol, increases lung cancer in smokers and nonsmokers. The effect is specific to supplementation dose as no lung damage has been detected in those who are exposed to cigarette smoke and who ingest a physiological dose of β-carotene (6 mg), in contrast to high pharmacological dose (30 mg).^[8]^[30].

Increases in lung cancer have been attributed to the tendency of β-carotene to oxidize,^[31] yet based on the pharmacokinetics of β-carotene absorption and transport through the intestine and the lack of specific β-carotene transporters, it is unlikely that β-carotene reaches the lung of smokers in sufficient quantities.^[32] Additional research is required to understand the link between the increased risk of cancer and all-cause mortality following β-carotene supplementation.

Additionally, supplemental, high-dose β-carotene may increase the risk of prostate cancer, intracerebral hemorrhage, and cardiovascular and total mortality irrespective of smoking status.^[8]^[9]

Industrial sources

β-carotene is industrially made either by total synthesis (see Retinol § Industrial synthesis) or by extraction from biological sources such as vegetables, microalgae (especially Dunaliella salina), and genetically-engineered microbes. The synthetic path is low-cost and high-yield.^[33]

Research

Medical authorities generally recommend obtaining beta-carotene from food rather than dietary supplements.^[8] A 2013 meta-analysis of randomized controlled trials concluded that high-dosage (≥9.6 mg/day) beta-carotene supplementation is associated with a 6% increase in the risk of all-cause mortality, while low-dosage (<9.6 mg/day) supplementation does not have a significant effect on mortality.^[34] Research is insufficient to determine whether a minimum level of beta-carotene consumption is necessary for human health and to identify what problems might arise from insufficient beta-carotene intake.^[35] However, a 2018 meta-analysis mostly of prospective cohort studies found that both dietary and circulating beta-carotene are associated with a lower risk of all-cause mortality. The highest circulating beta-carotene category, compared to the lowest, correlated with a 37% reduction in the risk of all-cause mortality, while the highest dietary beta-carotene intake category, compared to the lowest, was linked to an 18% decrease in the risk of all-cause mortality.^[36]

Macular degeneration

Age-related macular degeneration (AMD) represents the leading cause of irreversible blindness in elderly people. AMD is an oxidative stress, retinal disease that affects the macula, causing progressive loss of central vision.^[37] β-carotene content is confirmed in human retinal pigment epithelium.^[16] Reviews reported mixed results for observational studies, with some reporting that diets higher in β-carotene correlated with a decreased risk of AMD whereas other studies reporting no benefits.^[38] Reviews reported that for intervention trials using only β-carotene, there was no change to risk of developing AMD.^[8]^[38]^[39]

Cancer

A meta-analysis concluded that supplementation with β-carotene does not appear to decrease the risk of cancer overall, nor specific cancers including: pancreatic, colorectal, prostate, breast, melanoma, or skin cancer generally.^[8]^[40] High levels of β-carotene may increase the risk of lung cancer in current and former smokers.^[8]^[41] Results are not clear for thyroid cancer.^[42]

Cataract

A Cochrane review looked at supplementation of β-carotene, vitamin C, and vitamin E, independently and combined, on people to examine differences in risk of cataract, cataract extraction, progression of cataract, and slowing the loss of visual acuity. These studies found no evidence of any protective effects afforded by β-carotene supplementation on preventing and slowing age-related cataract.^[43] A second meta-analysis compiled data from studies that measured diet-derived serum beta-carotene and reported a not statistically significant 10% decrease in cataract risk.^[44]

Erythropoietic protoporphyria

High doses of β-carotene (up to 180 mg per day) may be used as a treatment for erythropoietic protoporphyria, a rare inherited disorder of sunlight sensitivity, without toxic effects.^[8]^[9]

Food drying

Foods rich in carotenoid dyes show discoloration upon drying. This is due to thermal degradation of carotenoids, possibly via isomerization and oxidation reactions.^[45]

References

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[Hursthouse-1] Hursthouse MB, Nathani SC, Moss GP (2004). "CSD Entry: CARTEN02". Cambridge Structural Database: Access Structures. Cambridge Crystallographic Data Centre. doi:10.5517/cc8j3mh. Retrieved 9 July 2022.

[Senge-2] Senge MO, Hope H, Smith KM (1992). "Structure and Conformation of Photosynthetic Pigments and Related Compounds 3. Crystal Structure of β-Carotene". Z. Naturforsch. C. 47 (5–6): 474–476. doi:10.1515/znc-1992-0623. S2CID 100905826.

[Scifinder-3] "SciFinder – CAS Registry Number 7235-40-7". Retrieved 21 October 2009.

[r1-4] Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. p. 3.94. ISBN 978-1439855119.

[pubchem-5] "Beta-carotene". PubChem, US National Library of Medicine. 27 January 2024. Retrieved 31 January 2024.

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@@ Line 1: / Line 1: @@
-{{short description|Chemical compound}}
+{{Short description|Red-orange pigment of the terpenoids class}}
+{{cs1 config|name-list-style=vanc|display-authors=6}}
-{{distinguish|beta-keratin}}
+{{Distinguish|beta-keratin}}
-{{use dmy dates |date=April 2021}}
+{{Use dmy dates|date=February 2024}}
 {{DISPLAYTITLE:β-Carotene}}
 {{Chembox
@@ Line 17: / Line 18: @@
 | ImageSize1 = 250
 | ImageAlt1 = Ball-and-stick model
-| ImageCaption1 = [[Ball-and-stick model]]<ref name="Hursthouse">{{ cite journal | url = https://dx.doi.org/10.5517/cc8j3mh | title = CSD Entry: CARTEN02 | website = [[Cambridge Structural Database]]: Access Structures | year = 2004 | publisher = [[Cambridge Crystallographic Data Centre]] | doi = 10.5517/cc8j3mh | access-date = 2022-07-09 | first1 = M. B. | last1 = Hursthouse | first2 = S. C. | last2 = Nathani | first3 = G. P. | last3 = Moss }}</ref><ref name="Senge">{{ cite journal | title = Structure and Conformation of Photosynthetic Pigments and Related Compounds 3. Crystal Structure of β-Carotene | first1 = Mathias O. | last1 = Senge | first2 = Häkon | last2 = Hope | first3 = Kevin M. | last3 = Smith | journal = [[Zeitschrift für Naturforschung C|Z. Naturforsch. C]] | year = 1992 | volume = 47 | issue = 5–6 | pages = 474–476 | doi = 10.1515/znc-1992-0623 | s2cid = 100905826 }}</ref>
+| ImageCaption1 = [[Ball-and-stick model]]<ref name="Hursthouse">{{ cite journal | url = https://dx.doi.org/10.5517/cc8j3mh | title = CSD Entry: CARTEN02 | website = [[Cambridge Structural Database]]: Access Structures | year = 2004 | publisher = [[Cambridge Crystallographic Data Centre]] | doi = 10.5517/cc8j3mh | access-date = 9 July 2022 | first1 = M. B. | last1 = Hursthouse | first2 = S. C. | last2 = Nathani | first3 = G. P. | last3 = Moss }}</ref><ref name="Senge">{{ cite journal | title = Structure and Conformation of Photosynthetic Pigments and Related Compounds 3. Crystal Structure of β-Carotene | first1 = Mathias O. | last1 = Senge | first2 = Häkon | last2 = Hope | first3 = Kevin M. | last3 = Smith | journal = [[Zeitschrift für Naturforschung C|Z. Naturforsch. C]] | year = 1992 | volume = 47 | issue = 5–6 | pages = 474–476 | doi = 10.1515/znc-1992-0623 | s2cid = 100905826 | doi-access = free }}</ref>
 | ImageFile2 = Beta-carotene-from-xtal-3D-sf.png
 | ImageFile2_Ref = {{Chemboximage|correct|??}}
@@ Line 26: / Line 27: @@
 | ImageSize3 = 250
 | IUPACName = β,β-Carotene
-| PIN = 1,1′-[(1''E'',3''E'',5''E'',7''E'',9''E'',11''E'',13''E'',15''E'',17''E'')-3,7,12,16-Tetramethyloctadeca-1,3,5,7,9,11,13,15,17-nonaene-1,18-diyl]bis(2,6,6-trimethylcyclohex-1-ene)
+| SystematicName = 1,1′-[(1''E'',3''E'',5''E'',7''E'',9''E'',11''E'',13''E'',15''E'',17''E'')-3,7,12,16-Tetramethyloctadeca-1,3,5,7,9,11,13,15,17-nonaene-1,18-diyl]bis(2,6,6-trimethylcyclohex-1-ene)
-| OtherNames = Betacarotene <small>([[International nonproprietary name|INN]])</small>, β-Carotene,<ref name='Scifinder'>{{cite web|url=https://scifinder.cas.org |title=SciFinder – CAS Registry Number 7235-40-7|access-date=Oct 21, 2009}}</ref> Food Orange 5, Provitamin A
+| OtherNames = Betacarotene <small>([[International nonproprietary name|INN]])</small>, β-Carotene,<ref name='Scifinder'>{{cite web|url=https://scifinder.cas.org |title=SciFinder – CAS Registry Number 7235-40-7|access-date=21 October 2009}}</ref> Food Orange 5, Provitamin A
 |Section1={{Chembox Identifiers
 | CASNo = 7235-40-7
@@ Line 56: / Line 57: @@
 | MeltingPtC = 183
 | MeltingPt_ref =<ref name=r1>{{cite book | editor= Haynes, William M. | year = 2011 | title = CRC Handbook of Chemistry and Physics | edition = 92nd | publisher = [[CRC Press]] | isbn = 978-1439855119|page=3.94| title-link = CRC Handbook of Chemistry and Physics }}</ref>
-| MeltingPt_notes = <br> decomposes<ref name=sigma />
+| MeltingPt_notes = <br /> decomposes<ref name=sigma />
 | BoilingPtC = 654.7
-| BoilingPt_notes = <br> at 760 mmHg (101324 Pa)
+| BoilingPt_notes = <br /> at 760 mmHg (101324 Pa)
 | Solubility = Insoluble
-| SolubleOther = Soluble in [[carbon disulfide|CS<sub>2</sub>]], [[benzene]], [[chloroform|CHCl<sub>3</sub>]], [[ethanol]]<br> Insoluble in [[glycerin]]
+| SolubleOther = Soluble in [[carbon disulfide|CS<sub>2</sub>]], [[benzene]], [[chloroform|CHCl<sub>3</sub>]], [[ethanol]]<br /> Insoluble in [[glycerin]]
-| Solubility1 = 4.51 g/kg (20&nbsp;°C)<ref name=chemister>[http://chemister.ru/Database/properties-en.php?dbid=1&id=3518 β-carotene]. chemister.ru</ref> = 5.98 g/L (given BCM density of 1.3266 g/cm<sup>3</sup> at 20°C)
+| Solubility1 = 4.51 g/kg (20&nbsp;°C)<ref name="pubchem">{{cite web |title=Beta-carotene |url=https://pubchem.ncbi.nlm.nih.gov/compound/5280489 |publisher=PubChem, US National Library of Medicine |access-date=31 January 2024 |date=27 January 2024}}</ref> = 5.98 g/L (given BCM density of 1.3266 g/cm<sup>3</sup> at 20°C)
 | Solvent1 = dichloromethane
 | Solubility2 = 0.1 g/L
@@ Line 83: / Line 84: @@
 | NFPA-R = 0
 | FlashPtC = 103
-| FlashPt_ref = <ref name=sigma>[[Sigma-Aldrich|Sigma-Aldrich Co.]], [http://www.sigmaaldrich.com/catalog/product/sigma/22040 β-Carotene]. Retrieved on 2014-05-27.</ref>
+| FlashPt_ref = <ref name=sigma>[[Sigma-Aldrich|Sigma-Aldrich Co.]], [http://www.sigmaaldrich.com/catalog/product/sigma/22040 β-Carotene]. Retrieved on 27 May 2014.</ref>
 }}
 }}
-'''β-Carotene''' (''beta''-carotene) is an [[organic compound|organic]], strongly coloured red-orange [[pigment]] abundant in fungi,<ref name=":0">{{Cite journal|last1=Lee|first1=Soo Chan|last2=Ristaino|first2=Jean B.|last3=Heitman|first3=Joseph|date=13 December 2012|title=Parallels in Intercellular Communication in Oomycete and Fungal Pathogens of Plants and Humans|journal=PLOS Pathogens|volume=8|issue=12|pages=e1003028|doi=10.1371/journal.ppat.1003028|pmid=23271965|pmc=3521652}}</ref> plants, and fruits. It is a member of the [[carotene]]s, which are [[terpenoid]]s (isoprenoids), synthesized biochemically from eight [[isoprene]] units and thus having 40 [[carbon]]s. Among the carotenes, β-carotene is distinguished by having [[Carotene|beta-rings]] at both ends of the [[molecule]].<ref name=Hursthouse/><ref name=Senge/> β-Carotene is biosynthesized from [[geranylgeranyl pyrophosphate]].<ref name=Kirk/>
+'''β-Carotene''' (''beta''-carotene) is an [[organic compound|organic]], strongly colored red-orange [[pigment]] abundant in fungi,<ref name=":0">{{cite journal|last1=Lee|first1=Soo Chan|last2=Ristaino|first2=Jean B.|last3=Heitman|first3=Joseph|date=13 December 2012|title=Parallels in Intercellular Communication in Oomycete and Fungal Pathogens of Plants and Humans|journal=PLOS Pathogens|volume=8|issue=12|pages=e1003028|doi=10.1371/journal.ppat.1003028 |doi-access=free|pmid=23271965|pmc=3521652}}</ref> plants, and fruits. It is a member of the [[carotene]]s, which are [[terpenoid]]s (isoprenoids), synthesized biochemically from eight [[isoprene]] units and thus having 40 [[carbon]]s.
+Dietary β-carotene is a pro[[vitamin A]] compound, converting in the body to [[retinol]] (vitamin A).<ref name="lpi">{{cite web |title=α-Carotene, β-Carotene, β-Cryptoxanthin, Lycopene, Lutein, and Zeaxanthin |url=https://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals/carotenoids |publisher=Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis |access-date=31 January 2024 |date=October 2023}}</ref> In foods, it has rich content in [[carrot]]s, [[pumpkin]], [[spinach]], and [[sweet potato]].<ref name=lpi/> It is used as a [[dietary supplement]] and may be prescribed to treat [[erythropoietic protoporphyria]], an inherited condition of sunlight sensitivity.<ref name="mlp">{{cite web |title=Beta-carotene |url=https://medlineplus.gov/druginfo/natural/999.html |publisher=MedlinePlus, National Library of Medicine, US National Institutes of Health |access-date=31 January 2024 |date=27 January 2023}}</ref>
-In some [[Mucorales|Mucoralean]] fungi, β-carotene is a precursor to the synthesis of [[trisporic acid]].<ref name=":0" />
-β-carotene is the most common form of carotene in plants. When used as a [[food coloring]], it has the [[E number]] E160a.<ref name="isbn0-471-73518-3">{{cite book |author=Milne, George W. A. |title=Gardner's commercially important chemicals: synonyms, trade names, and properties |publisher=Wiley-Interscience |location=New York |year=2005 |isbn=978-0-471-73518-2 }}</ref>{{rp|119}} The structure was deduced by Karrer et al. in 1930.<ref>{{cite journal | title = Pflanzenfarbstoffe XXV. Über die Konstitution des Lycopins und Carotins | vauthors = Karrer P, Helfenstein A, Wehrli H | author4 = Wettstein, A. | journal = [[Helvetica Chimica Acta]] | volume = 13 | issue = 5 | pages = 1084–1099 | year = 1930 | doi = 10.1002/hlca.19300130532 }}</ref> In nature, β-carotene is a precursor (inactive form) to [[vitamin A]] via the action of [[beta-carotene 15,15'-monooxygenase]].<ref name="Kirk">{{citation
+β-carotene is the most common carotenoid in plants.<ref name=lpi/> When used as a [[food coloring]], it has the [[E number]] E160a.<ref name="isbn0-471-73518-3">{{cite book |author=Milne, George W. A. |title=Gardner's commercially important chemicals: synonyms, trade names, and properties |publisher=Wiley-Interscience |location=New York |year=2005 |isbn=978-0-471-73518-2 }}</ref>{{rp|119}} The structure was deduced in 1930.<ref>{{cite journal | title = Pflanzenfarbstoffe XXV. Über die Konstitution des Lycopins und Carotins | vauthors = Karrer P, Helfenstein A, Wehrli H | author4 = Wettstein, A. | journal = [[Helvetica Chimica Acta]] | volume = 13 | issue = 5 | pages = 1084–1099 | year = 1930 | doi = 10.1002/hlca.19300130532 }}</ref>
-| title = Kirk-Othmer Encyclopedia of Chemical Technology
-| author = Van Arnum, Susan D.
-| publisher = John Wiley
-| location = New York
-| issue = 45
-| pages =99–107
-| year = 1998
-| doi = 10.1002/0471238961.2209200101181421.a01
-| chapter = Vitamin A
-| isbn = 978-0-471-23896-6}}</ref>
-Isolation of β-carotene from fruits abundant in [[carotenoid]]s is commonly done using column [[chromatography]]. It can also be extracted from the beta-carotene rich algae, ''[[Dunaliella salina]]''.<ref>{{cite patent
+Isolation of β-carotene from fruits abundant in carotenoids is commonly done using column [[chromatography]]. It is industrially extracted from richer sources such as the algae ''[[Dunaliella salina]]''.<ref name=us4439629>{{cite patent
 | country = United States
 | number = 4439629
 | status = expired
 | title = Extraction Process for Beta-Carotene
-| pubdate = March 27, 1984
+| pubdate = 27 March 1984
 | gdate =
-| fdate = November 6, 1981
+| fdate = 6 November 1981
 | pridate =
 | inventor = Rüegg, Rudolf
@@ Line 118: / Line 109: @@
 | assign2 =
 | class =
-}}</ref> The separation of β-carotene from the mixture of other carotenoids is based on the polarity of a compound. β-Carotene is a non-polar compound, so it is separated with a non-polar solvent such as [[hexane]].<ref>{{cite journal | vauthors = Mercadante AZ, Steck A, Pfander H | title = Carotenoids from guava (Psidium guajava l.): isolation and structure elucidation | journal = Journal of Agricultural and Food Chemistry | volume = 47 | issue = 1 | pages = 145–51 | date = January 1999 | pmid = 10563863 | doi = 10.1021/jf980405r }}</ref> Being highly [[conjugated system|conjugated]], it is deeply colored, and as a [[hydrocarbon]] lacking functional groups, it is very [[lipophilic]].
+}}</ref> The separation of β-carotene from the mixture of other carotenoids is based on the polarity of a compound. β-Carotene is a non-polar compound, so it is separated with a non-polar solvent such as [[hexane]].<ref>{{cite journal | vauthors = Mercadante AZ, Steck A, Pfander H | title = Carotenoids from guava (Psidium guajava l.): isolation and structure elucidation | journal = Journal of Agricultural and Food Chemistry | volume = 47 | issue = 1 | pages = 145–51 | date = January 1999 | pmid = 10563863 | doi = 10.1021/jf980405r }}</ref> Being highly [[conjugated system|conjugated]], it is deeply colored, and as a [[hydrocarbon]] lacking functional groups, it is [[lipophilic]].
 ==Provitamin A activity==
-Plant carotenoids are the primary dietary source of [[provitamin]] A worldwide, with β-carotene as the best-known provitamin A carotenoid. Others include [[alpha-Carotene|α-carotene]] and [[cryptoxanthin|β-cryptoxanthin]]. Carotenoid absorption is restricted to the [[duodenum]] of the [[small intestine]]. One molecule of β-carotene can be cleaved by the intestinal enzyme ''β,β-carotene 15,15'-monooxygenase'' into two molecules of [[vitamin A]].<ref>{{Cite book | title = Conversion of β-carotene to retinal pigment | year = 2007 | vauthors =Biesalski HK, Chichili GR, Frank J, von Lintig J, Nohr D | volume = 75 | pages = 117–30| pmid=17368314 | doi = 10.1016/S0083-6729(06)75005-1 | series = Vitamins & Hormones | isbn = 978-0-12-709875-3| chapter = Conversion of β‐Carotene to Retinal Pigment }}</ref><ref>{{cite journal |vauthors=Eroglu A, Harrison EH |title=Carotenoid metabolism in mammals, including man: formation, occurrence, and function of apocarotenoids |journal=J Lipid Res |volume=54 |issue=7 |pages=1719–30 |date=July 2013 |pmid=23667178 |pmc=3679377 |doi=10.1194/jlr.R039537 |url=}}</ref>
+Plant carotenoids are the primary dietary source of [[provitamin]] A worldwide, with β-carotene as the best-known provitamin A carotenoid.<ref name=lpi/> Others include [[alpha-Carotene|α-carotene]] and [[cryptoxanthin|β-cryptoxanthin]].<ref name=lpi/> Carotenoid absorption is restricted to the [[duodenum]] of the [[small intestine]]. One molecule of β-carotene can be cleaved by the intestinal enzyme ''β,β-carotene 15,15'-monooxygenase'' into two molecules of vitamin A.<ref name=lpi/><ref>{{cite book | title = Conversion of β-carotene to retinal pigment | year = 2007 | vauthors =Biesalski HK, Chichili GR, Frank J, von Lintig J, Nohr D | volume = 75 | pages = 117–30| pmid=17368314 | doi = 10.1016/S0083-6729(06)75005-1 | series = Vitamins & Hormones | isbn = 978-0-12-709875-3}}</ref><ref>{{cite journal |vauthors=Eroglu A, Harrison EH |title=Carotenoid metabolism in mammals, including man: formation, occurrence, and function of apocarotenoids |journal=J Lipid Res |volume=54 |issue=7 |pages=1719–30 |date=July 2013 |pmid=23667178 |pmc=3679377 |doi=10.1194/jlr.R039537  |doi-access=free |url=}}</ref>
 ==Absorption, metabolism and excretion==
-As part of the digestive process, food-sourced carotenoids must be separated from plant cells and incorporated into lipid-containing micelles to be bioaccessible to intestinal [[enterocytes]]. If already extracted (or synthetic) and then presented in an oil-filled dietary supplement capsule, there is greater bioavailability compared to that from foods.<ref name=PKIN2020Carotenoids/> At the enterocyte cell wall, β-carotene is taken up by the membrane transporter protein scavenger receptor class B, type 1 (SCARB1). Absorbed β-carotene is then either incorporated as such into [[chylomicron]]s or first converted to retinal and then retinol, bound to [[RBP2|retinol binding protein 2]], before being incorporated into chylomicrons. The conversion process consists of one molecule of β-carotene cleaved by the enzyme [[beta-carotene 15,15'-dioxygenase]], which is encoded by the BC01 gene, into two molecules of retinal. When plasma retinol is in the normal range the gene expression for SCARB1 and BC01 are suppressed, creating a feedback loop that suppresses β-carotene absorption and conversion.<ref name=PKIN2020Carotenoids/> The majority of chylomicrons are taken up by the liver, then secreted into the blood repackaged into [[low density lipoprotein]]s (LDLs). From these circulating lipoproteins and the chylomicrons that bypassed the liver, β-carotene is taken into cells via receptor SCARB1. Human tissues differ in expression of SCARB1, and hence β-carotene content. Examples expressed as ng/g, wet weight: liver=479, lung=226, prostate=163 and skin=26.<ref name=PKIN2020Carotenoids/>
+As part of the digestive process, food-sourced carotenoids must be separated from plant cells and incorporated into lipid-containing micelles to be bioaccessible to intestinal [[enterocytes]].<ref name=lpi/> If already extracted (or synthetic) and then presented in an oil-filled dietary supplement capsule, there is greater bioavailability compared to that from foods.<ref name=PKIN2020Carotenoids/>
+At the enterocyte cell wall, β-carotene is taken up by the membrane transporter protein scavenger receptor class B, type 1 (SCARB1). Absorbed β-carotene is then either incorporated as such into [[chylomicron]]s or first converted to retinal and then retinol, bound to [[RBP2|retinol binding protein 2]], before being incorporated into chylomicrons.<ref name=lpi/> The conversion process consists of one molecule of β-carotene cleaved by the enzyme [[beta-carotene 15,15'-dioxygenase]], which is encoded by the BCO1 gene, into two molecules of retinal.<ref name=lpi/> When plasma retinol is in the normal range the gene expression for SCARB1 and BCO1 are suppressed, creating a feedback loop that suppresses β-carotene absorption and conversion.<ref name=PKIN2020Carotenoids/>
-Once taken up by peripheral tissue cells, the major usage of absorbed β-carotene is as a precursor to retinal via symmetric cleavage by the enzyme beta-carotene 15,15'-dioxygenase, which is encoded by the BC01 gene. A lesser amount is metabolized by the mitochondrial enzyme beta-carotene 9',10'-dioxygenase, which is encoded by the BC02 gene. The products of this asymmetric cleavage are two [[beta-ionone]] molecules and rosafluene. BC02 appears to be involved in preventing excessive accumulation of carotenoids; a BC02 defect in chickens results in yellow skin color due to accumulation in subcutaneous fat.<ref name="Babino2015">{{cite journal |vauthors=Babino D, Palczewski G, Widjaja-Adhi MA, Kiser PD, Golczak M, von Lintig J |title=Characterization of the Role of β-Carotene 9,10-Dioxygenase in Macular Pigment Metabolism |journal=J Biol Chem |volume=290 |issue=41 |pages=24844–57 |date=October 2015 |pmid=26307071 |pmc=4598995 |doi=10.1074/jbc.M115.668822 |url=|doi-access=free }}</ref><ref name=Wu2016>{{cite journal |vauthors=Wu L, Guo X, Wang W, Medeiros DM, Clarke SL, Lucas EA, Smith BJ, Lin D |title=Molecular aspects of β, β-carotene-9', 10'-oxygenase 2 in carotenoid metabolism and diseases |journal=Exp Biol Med (Maywood) |volume=241 |issue=17 |pages=1879–1887 |date=November 2016 |pmid=27390265 |pmc=5068469 |doi=10.1177/1535370216657900 |url=}}</ref>
+The majority of chylomicrons are taken up by the liver, then secreted into the blood repackaged into [[low density lipoprotein]]s (LDLs).<ref name=lpi/> From these circulating lipoproteins and the chylomicrons that bypassed the liver, β-carotene is taken into cells via receptor SCARB1. Human tissues differ in expression of SCARB1, and hence β-carotene content. Examples expressed as ng/g, wet weight: liver=479, lung=226, prostate=163 and skin=26.<ref name=PKIN2020Carotenoids/>
+Once taken up by peripheral tissue cells, the major usage of absorbed β-carotene is as a precursor to retinal via symmetric cleavage by the enzyme beta-carotene 15,15'-dioxygenase, which is encoded by the BCO1 gene.<ref name=lpi/> A lesser amount is metabolized by the mitochondrial enzyme beta-carotene 9',10'-dioxygenase, which is encoded by the BCO2 gene. The products of this asymmetric cleavage are two [[beta-ionone]] molecules and rosafluene. BCO2 appears to be involved in preventing excessive accumulation of carotenoids; a BCO2 defect in chickens results in yellow skin color due to accumulation in subcutaneous fat.<ref name="Babino2015">{{cite journal |vauthors=Babino D, Palczewski G, Widjaja-Adhi MA, Kiser PD, Golczak M, von Lintig J |title=Characterization of the Role of β-Carotene 9,10-Dioxygenase in Macular Pigment Metabolism |journal=J Biol Chem |volume=290 |issue=41 |pages=24844–57 |date=October 2015 |pmid=26307071 |pmc=4598995 |doi=10.1074/jbc.M115.668822 |url=|doi-access=free }}</ref><ref name=Wu2016>{{cite journal |vauthors=Wu L, Guo X, Wang W, Medeiros DM, Clarke SL, Lucas EA, Smith BJ, Lin D |title=Molecular aspects of β, β-carotene-9', 10'-oxygenase 2 in carotenoid metabolism and diseases |journal=Exp Biol Med (Maywood) |volume=241 |issue=17 |pages=1879–1887 |date=November 2016 |pmid=27390265 |pmc=5068469 |doi=10.1177/1535370216657900 |url=}}</ref>
 ==Conversion factors==
+For counting dietary vitamin A intake, β-carotene may be converted either using the newer retinol activity equivalents (RAE) or the older international unit (IU).<ref name=lpi/>
-Since 2001, the US Institute of Medicine uses retinol activity equivalents (RAE) for their Dietary Reference Intakes, defined as follows:<ref name=DRI_A>{{cite book|title=Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium and Zinc|year=2001|publisher=National Academy Press|location=(free download)|doi=10.17226/10026|pmid=25057538|isbn=978-0-309-07279-3|author1=Institute of Medicine (US) Panel on Micronutrients|s2cid=44243659}}</ref>
 ===Retinol activity equivalents (RAEs)===
+Since 2001, the US Institute of Medicine uses retinol activity equivalents (RAE) for their Dietary Reference Intakes, defined as follows:<ref name=lpi/><ref name=DRI_A>{{cite book|title=Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium and Zinc|year=2001|publisher=National Academy Press|location=(free download)|doi=10.17226/10026|pmid=25057538|isbn=978-0-309-07279-3|author1=Institute of Medicine (US) Panel on Micronutrients|s2cid=44243659}}</ref>
-&nbsp;µg RAE = 1&nbsp;µg retinol
+* 1&nbsp;μg RAE = 1&nbsp;μg retinol from food or supplements
-&nbsp;µg RAE = 2&nbsp;µg all-''trans''-β-carotene from supplements
+* 1&nbsp;μg RAE = 2&nbsp;μg all-''trans''-β-carotene from supplements
+* 1&nbsp;μg RAE = 12&nbsp;μg of all-''trans''-β-carotene from food
-&nbsp;µg RAE = 12&nbsp;µg of all-''trans''-β-carotene from food
+* 1&nbsp;μg RAE = 24&nbsp;μg α-carotene or β-cryptoxanthin from food
-&nbsp;µg RAE = 24&nbsp;µg α-carotene or β-cryptoxanthin from food
-RAE takes into account carotenoids' variable absorption and conversion to vitamin A by humans better than and replaces the older retinol equivalent (RE) (1&nbsp;µg RE = 1&nbsp;µg retinol, 6&nbsp;µg β-carotene, or 12&nbsp;µg α-carotene or β-cryptoxanthin).<ref name=DRI_A /> RE was developed 1967 by the United Nations/[[World Health Organization]] Food and Agriculture Organization (FAO/WHO).<ref>{{cite book|last= Food and Agriculture Organization/World Health Organization|year= 1967 |title= Requirement of Vitamin A, Thiamine, Riboflavin and Niacin|location= Rome |series= FAO Food and Nutrition Series B}}</ref>
+RAE takes into account carotenoids' variable absorption and conversion to vitamin A by humans better than and replaces the older retinol equivalent (RE) (1&nbsp;μg RE = 1&nbsp;μg retinol, 6&nbsp;μg β-carotene, or 12&nbsp;μg α-carotene or β-cryptoxanthin).<ref name=DRI_A /> RE was developed 1967 by the United Nations/[[World Health Organization]] Food and Agriculture Organization (FAO/WHO).<ref>{{cite book|publisher= Food and Agriculture Organization/World Health Organization|year= 1967 |title= Requirement of Vitamin A, Thiamine, Riboflavin and Niacin|location=Rome |series= FAO Food and Nutrition Series B}}</ref>
-Another older unit of vitamin A activity is the international unit (IU). Like retinol equivalent, the international unit does not take into account carotenoids' variable absorption and conversion to vitamin A by humans, as well as the more modern retinol activity equivalent. Unfortunately, food and supplement labels still generally use IU, but IU can be converted to the more useful retinol activity equivalent as follows:<ref name=DRI_A />
 ===International Units===
+Another older unit of vitamin A activity is the international unit (IU).<ref name=lpi/> Like retinol equivalent, the international unit does not take into account carotenoid variable absorption and conversion to vitamin A by humans, as well as the more modern retinol activity equivalent. Unfortunately, food and supplement labels still generally use IU, but IU can be converted to the more useful retinol activity equivalent as follows:<ref name=DRI_A />
-* 1&nbsp;µg RAE = 3.33 IU retinol
+* 1&nbsp;μg RAE = 3.33 IU retinol
 * 1 IU retinol = 0.3 μg RAE
 * 1 IU β-carotene from supplements = 0.3 μg RAE
@@ Line 152: / Line 144: @@
 ==Dietary sources==
-The average daily intake of β-carotene is in the range 2–7&nbsp;mg, as estimated from a pooled analysis of 500,000 women living in the US, Canada, and some European countries.<ref>{{cite journal |vauthors = Koushik A, Hunter DJ, Spiegelman D, Anderson KE, Buring JE, Freudenheim JL, Goldbohm RA, Hankinson SE, Larsson SC, Leitzmann M, Marshall JR, McCullough ML, Miller AB, Rodriguez C, Rohan TE, Ross JA, Schatzkin A, Schouten LJ, Willett WC, Wolk A, Zhang SM, Smith-Warner SA | display-authors = 6 | title = Intake of the major carotenoids and the risk of epithelial ovarian cancer in a pooled analysis of 10 cohort studies | journal = International Journal of Cancer | volume = 119 | issue = 9 | pages = 2148–54 | date = November 2006 | pmid = 16823847 | doi = 10.1002/ijc.22076 | s2cid = 22948131 | doi-access = free }}</ref> Beta-carotene is found in many foods and is sold as a [[dietary supplement]]. β-Carotene contributes to the orange color of many different fruits and vegetables. [[Vietnam]]ese [[gac]] (''Momordica cochinchinensis'' Spreng.) and crude [[palm oil]] are particularly rich sources, as are yellow and orange fruits, such as [[cantaloupe]], [[mangoes]], [[pumpkin]], and [[papayas]], and orange [[root vegetables]] such as [[carrots]] and [[sweet potato]]es.<!-- real yams are not particularly high --> The color of β-carotene is masked by [[chlorophyll]] in green [[leaf vegetable]]s such as [[spinach]], [[kale]], sweet potato leaves, and sweet [[gourd]] leaves.<ref>{{cite journal | vauthors = Kidmose U, Edelenbos M, Christensen LP, Hegelund E | title = Chromatographic determination of changes in pigments in spinach (Spinacia oleracea L.) during processing | journal = Journal of Chromatographic Science | volume = 43 | issue = 9 | pages = 466–72 | date = October 2005 | pmid = 16212792 | doi = 10.1093/chromsci/43.9.466 | doi-access = free }}</ref> Vietnamese gac and crude palm oil have the highest content of β-carotene of any known plant sources, 10 times higher than carrots, for example. However, gac is quite rare and unknown outside its native region of Southeast Asia, and crude palm oil is typically processed to remove the carotenoids before sale to improve the color and clarity.<ref>{{cite journal | vauthors = Mustapa AN, Manan ZA, Azizi CM, Setianto WB, Omar AM |url= http://www.cheme.utm.my/cheme/images/Research/Journal_Articles/2011/journal-16-2011.pdf |archive-url= https://web.archive.org/web/20140107040317/http://www.cheme.utm.my/cheme/images/Research/Journal_Articles/2011/journal-16-2011.pdf |url-status=dead |archive-date=2014-01-07 |title=Extraction of β-carotenes from palm oil mesocarp using sub-critical R134a |journal=Food Chemistry |volume=125 |pages=262–267 |doi=10.1016/j.foodchem.2010.08.042 |year=2011 }}</ref>
+The average daily intake of β-carotene is in the range 2–7&nbsp;mg, as estimated from a pooled analysis of 500,000 women living in the US, Canada, and some European countries.<ref>{{cite journal |vauthors = Koushik A, Hunter DJ, Spiegelman D, Anderson KE, Buring JE, Freudenheim JL, Goldbohm RA, Hankinson SE, Larsson SC, Leitzmann M, Marshall JR, McCullough ML, Miller AB, Rodriguez C, Rohan TE, Ross JA, Schatzkin A, Schouten LJ, Willett WC, Wolk A, Zhang SM, Smith-Warner SA | title = Intake of the major carotenoids and the risk of epithelial ovarian cancer in a pooled analysis of 10 cohort studies | journal = International Journal of Cancer | volume = 119 | issue = 9 | pages = 2148–54 | date = November 2006 | pmid = 16823847 | doi = 10.1002/ijc.22076 | s2cid = 22948131 | doi-access = free }}</ref> Beta-carotene is found in many foods and is sold as a [[dietary supplement]].<ref name=lpi/> β-Carotene contributes to the orange color of many different fruits and vegetables. [[Vietnam]]ese [[gac]] (''Momordica cochinchinensis'' Spreng.) and crude [[palm oil]] are particularly rich sources, as are yellow and orange fruits, such as [[cantaloupe]], [[mangoes]], [[pumpkin]], and [[papayas]], and orange [[root vegetables]] such as [[carrots]] and [[sweet potato]]es.<ref name=lpi/>
+The color of β-carotene is masked by [[chlorophyll]] in green [[leaf vegetable]]s such as [[spinach]], [[kale]], sweet potato leaves, and sweet [[gourd]] leaves.<ref name=lpi/><ref>{{cite journal | vauthors = Kidmose U, Edelenbos M, Christensen LP, Hegelund E | title = Chromatographic determination of changes in pigments in spinach (Spinacia oleracea L.) during processing | journal = Journal of Chromatographic Science | volume = 43 | issue = 9 | pages = 466–72 | date = October 2005 | pmid = 16212792 | doi = 10.1093/chromsci/43.9.466 | doi-access = free }}</ref>
-The U.S. Department of Agriculture lists high in β-carotene content.<ref>{{cite web|url=https://ods.od.nih.gov/pubs/usdandb/VitA-betaCarotene-Content.pdf#search=%22beta-carotene%22 |title=USDA National Nutrient Database for Standard Reference, Release 28 |date=28 October 2015 |access-date=5 February 2022}}</ref>
+The U.S. Department of Agriculture lists foods high in β-carotene content:<ref>{{cite web|url=https://ods.od.nih.gov/pubs/usdandb/VitA-betaCarotene-Content.pdf#search=%22beta-carotene%22 |title=USDA National Nutrient Database for Standard Reference, Release 28 |date=28 October 2015 |access-date=5 February 2022}}</ref>
-{| class="wikitable" style="float:right; clear:left; width:18em; text-align:center;"
+{| class="wikitable" style="float:right; clear:right; width:18em; text-align:center;"
 |-
 ! Food
@@ Line 184: / Line 178: @@
 ===No dietary requirement===
-Government and non-government organization have not set a dietary requirement for β-carotene.<ref name=PKIN2020Carotenoids/>
+Government and non-government organizations have not set a dietary requirement for β-carotene.<ref name=PKIN2020Carotenoids/>
 == Side effects ==
-Excess β-carotene is predominantly stored in the fat tissues of the body. The most common side effect of excessive β-carotene consumption is carotenodermia, a physically harmless condition that presents as a conspicuous [[orange (colour)|orange]] [[skin]] tint arising from deposition of the carotenoid in the outermost layer of the [[Epidermis (skin)|epidermis]].<ref name=PKIN2020VitA>{{cite book |vauthors=Blaner WS |title = Present Knowledge in Nutrition, Eleventh Edition |chapter = Vitamin A |editor=BP Marriott |editor2=DF Birt |editor3=VA Stallings|editor4=AA Yates |publisher = Academic Press (Elsevier) |year=2020 |location = London, United Kingdom |pages = 73–92 |isbn=978-0-323-66162-1}}</ref><ref name=PKIN2020Carotenoids>{{cite book |vauthors=von Lintig J |title = Present Knowledge in Nutrition, Eleventh Edition |chapter = Carotenoids |editor=BP Marriott |editor2=DF Birt |editor3=VA Stallings|editor4=AA Yates |publisher = Academic Press (Elsevier) |year=2020 |location = London, United Kingdom |pages = 531–49 |isbn=978-0-323-66162-1}}</ref>
+Excess β-carotene is predominantly stored in the fat tissues of the body.<ref name=lpi/> The most common side effect of excessive β-carotene consumption is [[carotenodermia]], a physically harmless condition that presents as a conspicuous [[orange (colour)|orange]] [[skin]] tint arising from deposition of the carotenoid in the outermost layer of the [[Epidermis (skin)|epidermis]].<ref name=lpi/><ref name=mlp/><ref name=PKIN2020Carotenoids>{{cite book |vauthors=von Lintig J |title = Present Knowledge in Nutrition, Eleventh Edition |chapter = Carotenoids |editor=BP Marriott |editor2=DF Birt |editor3=VA Stallings|editor4=AA Yates |publisher = Academic Press (Elsevier) |year=2020 |location = London, United Kingdom |pages = 531–49 |isbn=978-0-323-66162-1}}</ref><ref name=PKIN2020VitA>{{cite book |vauthors=Blaner WS |title = Present Knowledge in Nutrition, Eleventh Edition |chapter = Vitamin A |editor=BP Marriott |editor2=DF Birt |editor3=VA Stallings|editor4=AA Yates |publisher = Academic Press (Elsevier) |year=2020 |location = London, United Kingdom |pages = 73–92 |isbn=978-0-323-66162-1}}</ref>
 ===Carotenosis===
-[[Carotenosis|Carotenoderma]], also referred to as carotenemia, is a benign and reversible medical condition where an excess of dietary carotenoids results in orange discoloration of the outermost skin layer. It is associated with a high blood β-carotene value. This can occur after a month or two of consumption of beta-carotene rich foods, such as carrots, carrot juice, tangerine juice, mangos, or in Africa, red palm oil. β-carotene dietary supplements can have the same effect. The discoloration extends to palms and soles of feet, but not to the [[sclera|white of the eye]], which helps distinguish the condition from [[jaundice]]. Carotenodermia is reversible upon cessation of excessive intake.<ref>{{cite journal |vauthors=Maharshak N, Shapiro J, Trau H |title=Carotenoderma--a review of the current literature |journal=Int J Dermatol |volume=42 |issue=3 |pages=178–81 |date=March 2003 |pmid=12653910 |doi=10.1046/j.1365-4362.2003.01657.x |s2cid=27934066 |url=}}</ref> Consumption of greater than 30&nbsp;mg/day for a prolonged period has been confirmed as leading to carotenemia.<ref name=PKIN2020Carotenoids/><ref>{{cite journal|vauthors=Nasser Y, Jamal Z, Albuteaey M |title=Carotenemia |journal=StatPearls |volume= |issue=  |pages= |date= 11 August 2021 |pmid=30521299 |doi=10.1007/s00253-001-0902-7|s2cid=22232461 }}</ref>
+[[Carotenosis|Carotenoderma]], also referred to as carotenemia, is a benign and reversible medical condition where an excess of dietary carotenoids results in orange discoloration of the outermost skin layer.<ref name=lpi/> It is associated with a high blood β-carotene value. This can occur after a month or two of consumption of beta-carotene rich foods, such as carrots, carrot juice, tangerine juice, mangos, or in Africa, red palm oil. β-carotene dietary supplements can have the same effect. The discoloration extends to palms and soles of feet, but not to the [[sclera|white of the eye]], which helps distinguish the condition from [[jaundice]]. Carotenodermia is reversible upon cessation of excessive intake.<ref>{{cite journal |vauthors=Maharshak N, Shapiro J, Trau H |title=Carotenoderma--a review of the current literature |journal=Int J Dermatol |volume=42 |issue=3 |pages=178–81 |date=March 2003 |pmid=12653910 |doi=10.1046/j.1365-4362.2003.01657.x |s2cid=27934066 |url=|doi-access=free }}</ref> Consumption of greater than 30&nbsp;mg/day for a prolonged period has been confirmed as leading to carotenemia.<ref name=PKIN2020Carotenoids/><ref>{{cite journal|vauthors=Nasser Y, Jamal Z, Albuteaey M |title=Carotenemia |journal=StatPearls |volume= |issue=  |pages= |date= 11 August 2021 |pmid=30521299 |doi=10.1007/s00253-001-0902-7|s2cid=22232461 }}</ref>
 ===No risk for hypervitaminosis A===
-At the [[enterocyte]] cell wall, β-carotene is taken up by the membrane transporter protein scavenger receptor class B, type 1 (SCARB1). Absorbed β-carotene is then either incorporated as such into chylomicrons or first converted to retinal and then retinol, bound to [[RBP2|retinol binding protein 2]], before being incorporated into chylomicrons. The conversion process consists of one molecule of β-carotene cleaved by the enzyme [[beta-carotene 15,15'-dioxygenase]], which is encoded by the BC01 gene, into two molecules of retinal. When plasma retinol is in the normal range the gene expression for SCARB1 and BC01 are suppressed, creating a feedback loop that suppresses absorption and conversion. Because of these two mechanisms, high intake will not lead to [[hypervitaminosis A]].<ref name=PKIN2020Carotenoids/>
+At the [[enterocyte]] cell wall, β-carotene is taken up by the membrane transporter protein scavenger receptor class B, type 1 (SCARB1). Absorbed β-carotene is then either incorporated as such into chylomicrons or first converted to retinal and then retinol, bound to [[RBP2|retinol binding protein 2]], before being incorporated into chylomicrons. The conversion process consists of one molecule of β-carotene cleaved by the enzyme [[beta-carotene 15,15'-dioxygenase]], which is encoded by the BCO1 gene, into two molecules of retinal. When plasma retinol is in the normal range the gene expression for SCARB1 and BCO1 are suppressed, creating a feedback loop that suppresses absorption and conversion. Because of these two mechanisms, high intake will not lead to [[hypervitaminosis A]].<ref name=PKIN2020Carotenoids/>
 ===Drug interactions===
-β-Carotene can interact with medication used for lowering [[cholesterol]]. Taking them together can lower the effectiveness of these medications and is considered only a moderate interaction.<ref>{{cite web | last=Web MD | title=Beta-Carotene Interactions | url=http://www.webmd.com/vitamins-supplements/ingredientmono-999-BETA-CAROTENE.aspx?activeIngredientId=999&activeIngredientName=BETA-CAROTENE| access-date = 28 May 2012}}</ref> [[Bile acid sequestrant]]s and [[proton-pump inhibitor]]s can decrease absorption of β-carotene.<ref>{{cite web | last=Meschino Health | title=Comprehensive Guide to Beta-Carotene | url=http://www.meschinohealth.com/books/beta_carotene| access-date = 29 May 2012}}</ref> Consuming alcohol with β-carotene can decrease its ability to convert to retinol and could possibly result in [[hepatotoxicity]].<ref>{{cite journal | vauthors = Leo MA, Lieber CS | title = Alcohol, vitamin A, and beta-carotene: adverse interactions, including hepatotoxicity and carcinogenicity | journal = The American Journal of Clinical Nutrition | volume = 69 | issue = 6 | pages = 1071–85 | date = June 1999 | pmid = 10357725 | doi = 10.1093/ajcn/69.6.1071 | doi-access = free }}</ref>
+β-Carotene can interact with medication used for lowering [[cholesterol]].<ref name=lpi/> Taking them together can lower the effectiveness of these medications and is considered only a moderate interaction.<ref name=lpi/> [[Bile acid sequestrant]]s and [[proton-pump inhibitor]]s can decrease absorption of β-carotene.<ref>{{cite web | last=Meschino Health | title=Comprehensive Guide to Beta-Carotene | url=http://www.meschinohealth.com/books/beta_carotene| access-date = 29 May 2012}}</ref> Consuming alcohol with β-carotene can decrease its ability to convert to retinol and could possibly result in [[hepatotoxicity]].<ref>{{cite journal | vauthors = Leo MA, Lieber CS | title = Alcohol, vitamin A, and beta-carotene: adverse interactions, including hepatotoxicity and carcinogenicity | journal = The American Journal of Clinical Nutrition | volume = 69 | issue = 6 | pages = 1071–85 | date = June 1999 | pmid = 10357725 | doi = 10.1093/ajcn/69.6.1071 | doi-access = free }}</ref>
 ===β-Carotene and lung cancer in smokers===
-Chronic high doses of β-carotene supplementation increases the probability of lung cancer in [[Health effects of tobacco|smokers]].<ref>{{cite journal | vauthors = Tanvetyanon T, Bepler G | title = Beta-carotene in multivitamins and the possible risk of lung cancer among smokers versus former smokers: a meta-analysis and evaluation of national brands | journal = Cancer | volume = 113 | issue = 1 | pages = 150–7 | date = July 2008 | pmid = 18429004 | doi = 10.1002/cncr.23527 | s2cid = 33827601 | doi-access = free }}</ref> The effect is specific to supplementation dose as no [[lung]] damage has been detected in those who are exposed to cigarette smoke and who ingest a physiologic dose of β-carotene (6&nbsp;mg), in contrast to high pharmacologic dose (30&nbsp;mg). Therefore, the [[oncology]] from β-carotene is based on both cigarette smoke and high daily doses of β-carotene.<ref>{{cite journal | doi = 10.1351/pac200274081461 | title = Beta-carotene and lung cancer | author = Russel, R.M. | journal = [[Pure Appl. Chem.]] | volume = 74 | issue = 8 | pages = 1461–1467 | year = 2002| citeseerx = 10.1.1.502.6550 | s2cid = 15046337 }}</ref>
+Chronic high doses of β-carotene supplementation increases the probability of lung cancer in [[Health effects of tobacco|smokers]]<ref name=lpi/><ref>{{cite journal | vauthors = Tanvetyanon T, Bepler G | title = Beta-carotene in multivitamins and the possible risk of lung cancer among smokers versus former smokers: a meta-analysis and evaluation of national brands | journal = Cancer | volume = 113 | issue = 1 | pages = 150–7 | date = July 2008 | pmid = 18429004 | doi = 10.1002/cncr.23527 | s2cid = 33827601 | doi-access = free }}</ref> while its natural vitamer, retinol, increases lung cancer in smokers and nonsmokers. The effect is specific to supplementation dose as no [[lung]] damage has been detected in those who are exposed to cigarette smoke and who ingest a physiological dose of β-carotene (6&nbsp;mg), in contrast to high pharmacological dose (30&nbsp;mg).<ref name=lpi/><ref>{{cite journal | doi = 10.1351/pac200274081461 | title = Beta-carotene and lung cancer | author = Russel, R.M. | journal = [[Pure Appl. Chem.]] | volume = 74 | issue = 8 | pages = 1461–1467 | year = 2002| citeseerx = 10.1.1.502.6550 | s2cid = 15046337 }}</ref>.
-Increases in lung cancer may be due to the tendency of β-carotene to oxidize,<ref>{{cite journal | vauthors = Hurst JS, Saini MK, Jin GF, Awasthi YC, van Kuijk FJ | title = Toxicity of oxidized beta-carotene to cultured human cells | journal = Experimental Eye Research | volume = 81 | issue = 2 | pages = 239–43 | date = August 2005 | pmid = 15967438 | doi = 10.1016/j.exer.2005.04.002 }}</ref> and may hasten oxidation more than other food colors such as [[annatto]]. A β-carotene breakdown product suspected of causing cancer at high dose is ''trans''-β-apo-8'-carotenal (common [[apocarotenal]]), which has been found in one study to be mutagenic and genotoxic in cell cultures which do not respond to β-carotene itself.<ref>{{cite journal | vauthors = Alija AJ, Bresgen N, Sommerburg O, Siems W, Eckl PM | title = Cytotoxic and genotoxic effects of beta-carotene breakdown products on primary rat hepatocytes | journal = Carcinogenesis | volume = 25 | issue = 5 | pages = 827–31 | date = May 2004 | pmid = 14688018 | doi = 10.1093/carcin/bgh056 | doi-access = free }}</ref>
+Increases in lung cancer have been attributed to the tendency of β-carotene to oxidize,<ref>{{cite journal | vauthors = Hurst JS, Saini MK, Jin GF, Awasthi YC, van Kuijk FJ | title = Toxicity of oxidized beta-carotene to cultured human cells | journal = Experimental Eye Research | volume = 81 | issue = 2 | pages = 239–43 | date = August 2005 | pmid = 15967438 | doi = 10.1016/j.exer.2005.04.002 }}</ref> yet based on the pharmacokinetics of β-carotene absorption and transport through the intestine and the lack of specific β-carotene transporters, it is unlikely that β-carotene reaches the lung of smokers in sufficient quantities.<ref>{{Cite journal |last1=Babino |first1=Darwin |last2=Palczewski |first2=Grzegorz |last3=Widjaja-Adhi |first3=M. Airanthi K. |last4=Kiser |first4=Philip D. |last5=Golczak |first5=Marcin |last6=von Lintig |first6=Johannes |date=2015-10-09 |title=Characterization of the Role of β-Carotene 9,10-Dioxygenase in Macular Pigment Metabolism |journal=The Journal of Biological Chemistry |volume=290 |issue=41 |pages=24844–24857 |doi=10.1074/jbc.M115.668822 |doi-access=free |issn=1083-351X |pmc=4598995 |pmid=26307071}}</ref> Additional research is required to understand the link between the increased risk of cancer and all-cause mortality following β-carotene supplementation.
-Additionally, supplemental, high-dose β-carotene may increase the risk of [[prostate cancer]], [[intracerebral hemorrhage]], and cardiovascular and total mortality in people who smoke [[cigarette]]s or have a history of high-level exposure to [[asbestos]].<ref>[https://www.nlm.nih.gov/medlineplus/druginfo/natural/patient-betacarotene.html#Safety Beta-carotene], MedlinePlus</ref>
+Additionally, supplemental, high-dose β-carotene may increase the risk of [[prostate cancer]], [[intracerebral hemorrhage]], and cardiovascular and total mortality irrespective of smoking status.<ref name=lpi/><ref name=mlp/>
+== Industrial sources ==
+β-carotene is industrially made either by total synthesis (see {{section link|Retinol|Industrial synthesis
+}}) or by extraction from biological sources such as vegetables, microalgae (especially ''Dunaliella salina''), and genetically-engineered microbes. The synthetic path is low-cost and high-yield.<ref name="singh">{{cite journal |last1=Singh |first1=Rahul Vikram |last2=Sambyal |first2=Krishika |title=An overview of β-carotene production: Current status and future prospects |journal=Food Bioscience |date=June 2022 |volume=47 |pages=101717 |doi=10.1016/j.fbio.2022.101717|s2cid=248252973 }}<!-- some weird allegation of the two versions not being identical in cancer potential (also found in doi:10.1093/fqsafe/fyy004), I call BS. --></ref>
 ==Research==
-Medical authorities generally recommend obtaining beta-carotene from food rather than dietary supplements.<ref name=Web2016>{{cite web | last=WebMD | title=Find a Vitamin or Supplement – Beta Carotene | url=http://www.webmd.com/vitamins-supplements/ingredientmono-999-BETA-CAROTENE.aspx?activeIngredientId=999&activeIngredientName=BETA-CAROTENE | access-date = 29 May 2012}}</ref> Research is insufficient to determine whether a minimum level of beta-carotene consumption is necessary for human health and to identify what problems might arise from insufficient beta-carotene intake.<ref name=Impli>{{cite book|last1=Stargrove|first1=Mitchell|title= Herb, nutrient, and drug interactions : clinical implications and therapeutic strategies|date=2007-12-20|publisher=Mosby|isbn=978-0323029643|edition=1}}</ref>
+Medical authorities generally recommend obtaining beta-carotene from food rather than dietary supplements.<ref name=lpi/> A 2013 meta-analysis of [[randomized controlled trial]]s concluded that high-dosage (≥9.6 mg/day) beta-carotene supplementation is associated with a 6% increase in the risk of all-cause [[Mortality rate|mortality]], while low-dosage (<9.6 mg/day) supplementation does not have a significant effect on mortality.<ref name=Bjelakovic2014>{{cite journal | vauthors = Bjelakovic G, Nikolova D, Gluud C | title = Meta-regression analyses, meta-analyses, and trial sequential analyses of the effects of supplementation with beta-carotene, vitamin A, and vitamin E singly or in different combinations on all-cause mortality: do we have evidence for lack of harm? |journal = PLOS ONE| volume = 8 |issue = 9 |pages = e74558 |date = 2013 |pmid = 24040282 |pmc = 3765487 | doi = 10.1371/journal.pone.0074558 | bibcode = 2013PLoSO...874558B | doi-access = free }}</ref> Research is insufficient to determine whether a minimum level of beta-carotene consumption is necessary for human health and to identify what problems might arise from insufficient beta-carotene intake.<ref name=Impli>{{cite book|last1=Stargrove|first1=Mitchell|title= Herb, nutrient, and drug interactions : clinical implications and therapeutic strategies|date=20 December 2007|publisher=Mosby|isbn=978-0323029643|edition=1}}</ref> However, a 2018 meta-analysis mostly of [[prospective cohort studies]] found that both dietary and [[Blood test|circulating]] beta-carotene are associated with a lower risk of all-cause mortality. The highest circulating beta-carotene category, compared to the lowest, correlated with a 37% reduction in the risk of all-cause mortality, while the highest dietary beta-carotene intake category, compared to the lowest, was linked to an 18% decrease in the risk of all-cause mortality.<ref name="pmid30239557">{{cite journal| vauthors=Jayedi A, Rashidy-Pour A, Parohan M, Zargar MS, Shab-Bidar S| title=Dietary Antioxidants, Circulating Antioxidant Concentrations, Total Antioxidant Capacity, and Risk of All-Cause Mortality: A Systematic Review and Dose-Response Meta-Analysis of Prospective Observational Studies. | journal=Adv Nutr | year= 2018 | volume= 9 | issue= 6 | pages= 701–716 | pmid=30239557 | doi=10.1093/advances/nmy040 | pmc=6247336}} </ref>
 ===Macular degeneration===
 {{Main|Macular degeneration}}
-Age-related macular degeneration (AMD) represents the leading cause of irreversible blindness in elderly people. AMD is an oxidative stress, retinal disease that affects the macula, causing progressive loss of central vision.<ref name="DiCarlo2021">{{cite journal |vauthors=Di Carlo E, Augustin AJ |title=Prevention of the Onset of Age-Related Macular Degeneration |journal=J Clin Med |volume=10 |issue=15 |date=July 2021 |page=3297 |pmid=34362080 |pmc=8348883 |doi=10.3390/jcm10153297 |url=|doi-access=free }}</ref> β-carotene content is confirmed in human retinal pigment epithelium.<ref name=PKIN2020Carotenoids/> Reviews reported mixed results for observational studies, with some reporting that diets higher in β-carotene correlated with a decreased risk of AMD whereas other studies reporting no benefits.<ref name="Gorus2017">{{cite journal |vauthors=Gorusupudi A, Nelson K, Bernstein PS |title=The Age-Related Eye Disease 2 Study: Micronutrients in the Treatment of Macular Degeneration |journal=Adv Nutr |volume=8 |issue=1 |pages=40–53 |date=January 2017 |pmid=28096126 |pmc=5227975 |doi=10.3945/an.116.013177 |url=}}</ref> Reviews reported that for intervention trials using only β-carotene, there was no change to risk of developing AMD.<ref name="Gorus2017"/><ref>{{cite journal |vauthors=Evans JR, Lawrenson JG |title=Antioxidant vitamin and mineral supplements for preventing age-related macular degeneration |journal=Cochrane Database Syst Rev |volume=2017 |issue= 7|pages=CD000253 |date=July 2017 |pmid=28756617 |pmc=6483250 |doi=10.1002/14651858.CD000253.pub4 |url=}}</ref>
+Age-related macular degeneration (AMD) represents the leading cause of irreversible blindness in elderly people. AMD is an oxidative stress, retinal disease that affects the macula, causing progressive loss of central vision.<ref name="DiCarlo2021">{{cite journal |vauthors=Di Carlo E, Augustin AJ |title=Prevention of the Onset of Age-Related Macular Degeneration |journal=J Clin Med |volume=10 |issue=15 |date=July 2021 |page=3297 |pmid=34362080 |pmc=8348883 |doi=10.3390/jcm10153297 |url=|doi-access=free }}</ref> β-carotene content is confirmed in human retinal pigment epithelium.<ref name=PKIN2020Carotenoids/> Reviews reported mixed results for observational studies, with some reporting that diets higher in β-carotene correlated with a decreased risk of AMD whereas other studies reporting no benefits.<ref name="Gorus2017">{{cite journal |vauthors=Gorusupudi A, Nelson K, Bernstein PS |title=The Age-Related Eye Disease 2 Study: Micronutrients in the Treatment of Macular Degeneration |journal=Adv Nutr |volume=8 |issue=1 |pages=40–53 |date=January 2017 |pmid=28096126 |pmc=5227975 |doi=10.3945/an.116.013177 |url=}}</ref> Reviews reported that for intervention trials using only β-carotene, there was no change to risk of developing AMD.<ref name=lpi/><ref name="Gorus2017"/><ref>{{cite journal |vauthors=Evans JR, Lawrenson JG |title=Antioxidant vitamin and mineral supplements for preventing age-related macular degeneration |journal=Cochrane Database Syst Rev |volume=2017 |issue= 7|pages=CD000253 |date=July 2017 |pmid=28756617 |pmc=6483250 |doi=10.1002/14651858.CD000253.pub4 |url=}}</ref>
 ===Cancer===
-A meta-analysis concluded that supplementation with β-carotene does not appear to decrease the risk of cancer overall, nor specific cancers including: pancreatic, colorectal, prostate, breast, melanoma, or skin cancer generally.<ref name=Druesne2010>{{cite journal | vauthors = Druesne-Pecollo N, Latino-Martel P, Norat T, Barrandon E, Bertrais S, Galan P, Hercberg S | title = Beta-carotene supplementation and cancer risk: a systematic review and metaanalysis of randomized controlled trials | journal = International Journal of Cancer | volume = 127 | issue = 1 | pages = 172–84 | date = July 2010 | pmid = 19876916 | doi = 10.1002/ijc.25008 | s2cid = 24850769 | doi-access = free }}</ref> High levels of β-carotene may increase the risk of lung cancer in current and former smokers.<ref>{{cite journal | vauthors = Misotti AM, Gnagnarella P | title = Vitamin supplement consumption and breast cancer risk: a review | journal = ecancermedicalscience | volume = 7 | pages = 365 | date = October 2013 | pmid = 24171049 | pmc = 3805144 | doi = 10.3332/ecancer.2013.365 }}</ref> This is likely because beta-carotene is unstable in cigarette smoke-exposed lungs where it forms oxidized metabolites that can induce carcinogen-bioactivating enzymes.<ref>{{cite journal | vauthors = Russell RM | title = The enigma of beta-carotene in carcinogenesis: what can be learned from animal studies | journal = The Journal of Nutrition | volume = 134 | issue = 1 | pages = 262S–268S | date = January 2004 | pmid = 14704331 | doi = 10.1093/jn/134.1.262S | doi-access = free }}</ref> Results are not clear for thyroid cancer.<ref>{{cite journal | vauthors = Zhang LR, Sawka AM, Adams L, Hatfield N, Hung RJ | title = Vitamin and mineral supplements and thyroid cancer: a systematic review | journal = European Journal of Cancer Prevention | volume = 22 | issue = 2 | pages = 158–68 | date = March 2013 | pmid = 22926510 | doi = 10.1097/cej.0b013e32835849b0 | s2cid = 35660646 }}</ref> In a single, small clinical study published in 1989, natural beta-carotene appeared to reduce premalignant gastric lesions.<ref name=Impli/>{{rp|177}}
+A meta-analysis concluded that supplementation with β-carotene does not appear to decrease the risk of cancer overall, nor specific cancers including: pancreatic, colorectal, prostate, breast, melanoma, or skin cancer generally.<ref name=lpi/><ref name=Druesne2010>{{cite journal | vauthors = Druesne-Pecollo N, Latino-Martel P, Norat T, Barrandon E, Bertrais S, Galan P, Hercberg S | title = Beta-carotene supplementation and cancer risk: a systematic review and metaanalysis of randomized controlled trials | journal = International Journal of Cancer | volume = 127 | issue = 1 | pages = 172–84 | date = July 2010 | pmid = 19876916 | doi = 10.1002/ijc.25008 | s2cid = 24850769 | doi-access = free }}</ref> High levels of β-carotene may increase the risk of lung cancer in current and former smokers.<ref name=lpi/><ref>{{cite journal | vauthors = Misotti AM, Gnagnarella P | title = Vitamin supplement consumption and breast cancer risk: a review | journal = ecancermedicalscience | volume = 7 | pages = 365 | date = October 2013 | pmid = 24171049 | pmc = 3805144 | doi = 10.3332/ecancer.2013.365 }}</ref> Results are not clear for thyroid cancer.<ref>{{cite journal | vauthors = Zhang LR, Sawka AM, Adams L, Hatfield N, Hung RJ | title = Vitamin and mineral supplements and thyroid cancer: a systematic review | journal = European Journal of Cancer Prevention | volume = 22 | issue = 2 | pages = 158–68 | date = March 2013 | pmid = 22926510 | doi = 10.1097/cej.0b013e32835849b0 | s2cid = 35660646 }}</ref>
 ===Cataract===
-A [[Cochrane Collaboration|Cochrane review]] looked at supplementation of β-carotene, vitamin C, and vitamin E, independently and combined, on people to examine differences in risk of [[cataract]], cataract extraction, progression of cataract, and slowing the loss of visual acuity. These studies found no evidence of any protective effects afforded by β-carotene supplementation on preventing and slowing age-related cataract.<ref name=Cochrane2012>{{cite journal | vauthors = Mathew MC, Ervin AM, Tao J, Davis RM | title = Antioxidant vitamin supplementation for preventing and slowing the progression of age-related cataract | journal = The Cochrane Database of Systematic Reviews | volume = 6 | issue = 6 | pages = CD004567 | date = June 2012 | pmid = 22696344 | pmc = 4410744 | doi = 10.1002/14651858.CD004567.pub2 }}</ref> A second meta-analysis compiled data from studies that measured diet-derived serum beta-carotene and reported a not statistically significant 10% decrease in cataract risk.<ref>{{cite journal | vauthors = Cui YH, Jing CX, Pan HW | title = Association of blood antioxidants and vitamins with risk of age-related cataract: a meta-analysis of observational studies | journal = The American Journal of Clinical Nutrition | volume = 98 | issue = 3 | pages = 778–86 | date = September 2013 | pmid = 23842458 | doi = 10.3945/ajcn.112.053835 | doi-access = free }}</ref>
+A [[Cochrane Collaboration|Cochrane review]] looked at supplementation of β-carotene, vitamin C, and vitamin E, independently and combined, on people to examine differences in risk of [[cataract]], cataract extraction, progression of cataract, and slowing the loss of visual acuity. These studies found no evidence of any protective effects afforded by β-carotene supplementation on preventing and slowing age-related cataract.<ref name=Cochrane2012>{{cite journal | vauthors = Mathew MC, Ervin AM, Tao J, Davis RM | title = Antioxidant vitamin supplementation for preventing and slowing the progression of age-related cataract | journal = The Cochrane Database of Systematic Reviews | volume = 2012 | issue = 6 | pages = CD004567 | date = June 2012 | pmid = 22696344 | pmc = 4410744 | doi = 10.1002/14651858.CD004567.pub2 }}</ref> A second meta-analysis compiled data from studies that measured diet-derived serum beta-carotene and reported a not statistically significant 10% decrease in cataract risk.<ref>{{cite journal | vauthors = Cui YH, Jing CX, Pan HW | title = Association of blood antioxidants and vitamins with risk of age-related cataract: a meta-analysis of observational studies | journal = The American Journal of Clinical Nutrition | volume = 98 | issue = 3 | pages = 778–86 | date = September 2013 | pmid = 23842458 | doi = 10.3945/ajcn.112.053835 | doi-access = free }}</ref>
+===Erythropoietic protoporphyria===
+High doses of β-carotene (up to 180 mg per day) may be used as a treatment for [[erythropoietic protoporphyria]], a rare inherited disorder of sunlight sensitivity, without toxic effects.<ref name=lpi/><ref name=mlp/>
 === Food drying ===
-Caretenoids were found to be susceptible to a [[Thermal decomposition|thermal degradation]] and discoloration upon drying, which are believed to associated with [[isomerization]] and oxidation reactions.<ref>{{Cite journal |last1=Song |first1=Jiangfeng |last2=Wang |first2=Xiaoping |last3=Li |first3=Dajing |last4=Liu |first4=Chunquan |date=2017-12-18 |title=Degradation kinetics of carotenoids and visual colour in pumpkin (Cucurbita maxima L.) slices during microwave-vacuum drying |url=https://www.tandfonline.com/doi/full/10.1080/10942912.2017.1306553 |journal=International Journal of Food Properties |language=en |volume=20 |issue=sup1 |pages=S632–S643 |doi=10.1080/10942912.2017.1306553 |s2cid=90336692 |issn=1094-2912}}</ref>
+Foods rich in carotenoid dyes show discoloration upon drying. This is due to [[Thermal decomposition|thermal degradation]] of carotenoids, possibly via [[isomerization]] and oxidation reactions.<ref>{{cite journal |last1=Song |first1=Jiangfeng |last2=Wang |first2=Xiaoping |last3=Li |first3=Dajing |last4=Liu |first4=Chunquan |date=18 December 2017 |title=Degradation kinetics of carotenoids and visual colour in pumpkin (Cucurbita maxima L.) slices during microwave-vacuum drying |journal=International Journal of Food Properties |language=en |volume=20 |issue=sup1 |pages=S632–S643 |doi=10.1080/10942912.2017.1306553 |s2cid=90336692 |issn=1094-2912|doi-access=free }}</ref>
 == See also ==
@@ Line 228: / Line 229: @@
 == References ==
-{{reflist|30em}}
+{{Reflist}}
 {{Carotenoids}}
@@ Line 234: / Line 235: @@
 {{Emollients and protectives}}
 {{Terpenoids}}
+{{Authority control}}
 {{DEFAULTSORT:Carotene, Beta-}}

v t e Carotenoids
Carotenes (C₄₀)	α-Carotene β-Carotene γ-Carotene δ-Carotene ε-Carotene ζ-Carotene Lycopene Neurosporene Phytoene Phytofluene Torulene Lycopersene
Xanthophylls (C₄₀)	Antheraxanthin Astaxanthin Canthaxanthin Citranaxanthin Cryptoxanthin Diadinoxanthin Diatoxanthin Dinoxanthin Echinenone Flavoxanthin Fucoxanthin Lutein Neoxanthin Rhodoxanthin Rubixanthin Violaxanthin Zeaxanthin Zeinoxanthin
Apocarotenoids (C_<40)	Abscisic acid Apocarotenal Bixin Crocetin Food orange 7 Ionones Peridinin
Vitamin A retinoids (C₂₀)	Retinal Retinoic acid Retinol
Retinoid drugs	Acitretin Alitretinoin Bexarotene Etretinate Fenretinide Isotretinoin Tazarotene Temarotene Tretinoin Zuretinol acetate

v t e Emollients and protectives (D02)
Emollients and protectives	Paraffin Carbamide
Protectives against UV-radiation	Aminobenzoic acid Octinoxate Betacarotene