Gamma-carotene

Other Names

2-(3,7,12,16,20,24-hexamethylpentacosa-1,3,5,7,9,11,13,15,17,19,23-undecaenyl)-1,3,3-trimethyl-cyclohexene2-(3,7,12,16,20,24-hexamethylpentacosa-1,3,5,7,9,11,13,15,17,19,23-undecaenyl)-1,3,3-trimethylcyclohexene2-[(1E,3E,5E,7E,9E,11E,13E,15E,17E,19E)-3,7,12,16,20,24-hexamethylpentacosa-1,3,5,7,9,11,13,15,17,19,23-undecaen-1-yl]-1,3,3-trimethylcyclohex-1-ene2-[(1E,3E,5E,7E,9E,11E,13E,15E,17E,19E)-3,7,12,16,20,24-hexamethylpentacosa-1,3,5,7,9,11,13,15,17,19,23-undecaenyl]-1,3,3-trimethyl-cyclohexenebeta,psi-CaroteneDH369M0SOEg-CaroteneGAMMACAROTENEUNII-DH369M0SOEβ,ψ-Caroteneβ,ψ-Carotèneβ,ψ-Carotinγ-Carotene

Synopsis

Gamma-Carotene (γ-Carotene): A Comprehensive Reference

1. Identity, Chemistry, and Nomenclature

Chemical Names and Classification

Gamma-carotene (γ-carotene) is a carotenoid, and is a biosynthetic intermediate for cyclized carotenoid synthesis in plants. It belongs to the subclass of pure hydrocarbon carotenoids known as carotenes. Hydrocarbon carotenoids — those exclusively containing carbon and hydrogen atoms in their molecules — are termed carotenes, and γ-carotene is classified among them alongside α-carotene, β-carotene, ζ-carotene, lycopene, neurosporene, phytoene, and phytofluene.

In formal systematic nomenclature, gamma-carotene is designated as β,ψ-carotene, reflecting the nature of its two terminal ring structures: one β-ionone ring (cyclized) and one ψ-end (open, uncyclized, as in lycopene). Gamma-carotene is defined as a monocyclic carotenoid (β,ψ-carotene) that is found in certain foods, such as Eugenia uniflora, typically in lower concentrations compared to other carotenoids like β-carotene.

Its molecular formula is C₄₀H₅₆, making it, like all carotenes, a tetraterpene. Its molecular formula is C₄₀H₅₆, like many carotenoids, but the double-bond pattern shifts its absorption peak. Since they are hydrocarbons, and therefore contain no oxygen, carotenes are fat-soluble and insoluble in water, in contrast with the xanthophylls, which contain oxygen and thus are less chemically hydrophobic.

Structural Relationship to Other Carotenoids

γ-Carotene is the product of cyclization of lycopene at one end, whereas in β-carotene, both ends are cyclized. This structural intermediate position between lycopene and the bicyclic carotenes (α- and β-carotene) is fundamental to its biological properties. It is formed from cyclization of lycopene by lycopene cyclase epsilon.

Carotenes are found in plants in two primary forms designated by characters from the Greek alphabet: alpha-carotene (α-carotene) and beta-carotene (β-carotene). Gamma-, delta-, epsilon-, and zeta-carotene (γ, δ, ε, and ζ-carotene) also exist. The most important representatives of the carotene subgroup are lycopene, α-, β-, γ-, and δ-carotene, phytofluene, torulene, as well as shorter and longer terpenoids.

Physical and Chemical Properties

Chemically, γ-carotene belongs to the carotenoid family, specifically as a non-polar hydrocarbon. It is fat-soluble, light-sensitive, and fairly stable when stored cool and dark, though it degrades with heat and oxygen over time. Its color, ranging from pale yellow through bright orange to deep red, is directly related to its structure, especially the length of the conjugation. Carotenoids are chemically unstable and prone to oxidation in the presence of light, heat, oxygen, acids, and metal ions.

Naturally, most carotenoids occur as all-trans- or different cis-isomers (9-cis, 13-cis, 15-cis isomers), with each double bond in the carbon chain of the carotenoid being able to exist in either the trans or the cis configuration.

2. Natural Sources and Occurrence

Plant and Fruit Sources

The bicyclic α-carotene (β,ε-carotene) and the monocyclic γ-carotene (β,ψ-carotene) sometimes accompany β-carotene in foods, generally at much lower concentrations. Substantial amounts of γ-carotene are found in Eugenia uniflora. This South American fruit, known as pitanga or Surinam cherry, has been characterized as a particularly concentrated source. In one study, the carotenoids of the pitanga fruit from two Brazilian states and at two stages of ripening were determined by HPLC. Ripe pitanga from Campinas had significantly higher (all-E)-lycopene and (all-E)-gamma-carotene (1.6 vs. 3.8 μg/g) levels. Pitanga was found to be one of the richest fruit sources of carotenoids, particularly lycopene, but the processed products had much lower lycopene content.

Gamma-carotene is also found in apricots (Prunus armeniaca), where it has been consistently identified as a minor but detectable carotenoid component. Among 37 apricot varieties studied, the total carotenoid content ranged from 1,512 to 16,500 μg per 100 g of edible portion, with beta-carotene as the main pigment followed by beta-cryptoxanthin and gamma-carotene. Analyzing various cultivars with white, yellow, light orange, and orange flesh, the percentages of β-carotene, β-cryptoxanthin, and γ-carotene did not follow any particular pattern.

γ-Carotene is found concentrated in the chloroplasts and chromoplasts of colorful plants, especially in orange- and yellow-pigmented tissues. It is notably present in carrot peel, especially in heirloom varieties, and in red palm oil, which contains mixed carotenes including γ-carotene.

The most abundant carotenoids available through various food sources for human consumption are beta-carotene, alpha-carotene, gamma-carotene, lycopene, lutein, zeaxanthin, beta-cryptoxanthin, and astaxanthin. Gamma-carotene, however, is always a minor component; it is never the dominant carotenoid in any commercially significant food.

Microbial and Algal Sources

γ-Carotene is a carotenoid, a class of pigments giving color to photosynthetic organisms. Specifically, γ-carotene may be derived from myxoxanthophyll found in cyanobacteria, Chlorobiaceae, and green non-sulfur bacteria (Chloroflexi).

Geological and Biomarker Context

γ-Carotene has tentatively been identified as a biomarker for green and purple sulfur bacteria in a sample from the 1.640 ± 0.003-Gyr-old Barney Creek Formation in Northern Australia, which comprises marine sediments. This finding is of interest in paleobiogeochemistry but not directly relevant to dietary or nutritional use.

3. Traditional and Historical Context

Pre-Scientific Use of Carotenoid-Rich Foods

Gamma-carotene was not isolated, named, or recognized as a distinct chemical entity in traditional medical systems. The concept of individual carotenoids is entirely modern. What traditional cultures across history used were whole foods containing mixtures of carotenoids, including γ-carotene, primarily without awareness of the specific compound. For this reason, the historical record pertains to the broader context of provitamin A carotenoid-rich diets and the relief of what is now recognized as vitamin A deficiency.

Night blindness, a condition in which a person cannot see in dim light, has been known since ancient Egyptian times, and Hippocrates, who lived 460–325 BC, recognized night blindness and recommended eating raw liver as a cure, thus establishing a link between night blindness and nutrition. Many physicians and scientists since observed that night blindness often accompanies malnutrition. Another eye disease presenting dryness of the cornea and conjunctiva (xerophthalmia), and in severe cases ulceration of the cornea (keratomalacia), was described as caused by "defective nutriment." It had been known as "hikan" in Japan since antiquity.

Vitamin A deficiency eye disease and night blindness were recognized by the ancient Egyptians and Greeks, and many authorities from Galen onward advocated liver as a curative. Outbreaks of night blindness were linked to nutritional causes in the 18th and 19th centuries. In these contexts, plant foods rich in carotenoids — including the foods that contain γ-carotene — were used empirically by traditional healers across Asia, Africa, and the Americas to treat or prevent visual impairment, though the underlying mechanisms were unknown.

Scientific Discovery of Carotene

The discovery of carotene from carrot juice is credited to Heinrich Wilhelm Ferdinand Wackenroder, a finding made during a search for antihelminthics, which he published in 1831. He obtained it in small ruby-red flakes soluble in ether, which when dissolved in fats gave "a beautiful yellow colour." The specific isomers of carotene — including γ-carotene — were only distinguished analytically in the twentieth century with the development of chromatographic and spectroscopic techniques.

4. Key Constituents and Mechanisms of Action

Provitamin A Activity

Out of around 600 structurally and functionally diverse natural carotenoid types, three major provitamin A isomers are the alpha, beta, and gamma isomers. Along with several other carotenoids, γ-carotene is a vitamer of vitamin A in herbivores and omnivores. Carotenoids with a cyclized beta-ionone ring can be converted to vitamin A, also known as retinol, by the enzyme beta-carotene 15,15'-dioxygenase; however, the bioconversion of γ-carotene to retinol has not been well-characterized.

Not all carotenoids have pro-vitamin A activity; the molecule must contain at least 11 carbons, at least one unsubstituted β (beta) ring, and conjugated double bonds — as is the case for β-carotene, γ-carotene, α-carotene, β-cryptoxanthin, and α-cryptoxanthin. To exhibit provitamin A activity, a carotenoid molecule must have at least one unsubstituted β-ionone ring and the correct number of methyl groups in the correct position in the polyene chain. γ-Carotene satisfies this structural criterion through its single β-ionone ring, but it can theoretically yield only one molecule of retinaldehyde upon central cleavage (unlike β-carotene, which can yield two), because only one of its two ends is cyclized.

Provitamin A carotenoids (β-carotene, α-carotene, γ-carotene, and β-cryptoxanthin) are essential for the development and maintenance of sight. In humans, the only known function of carotenoids is vitamin A activity (provitamin A carotenoids only). All other attributed roles represent proposed actions or epidemiological associations rather than established functions.

Singlet Oxygen Quenching and Antioxidant Mechanisms

The polyene chain of the carotenoid absorbs the excited energy of singlet oxygen, effectively stabilizing the energy transfer by delocalization along the chain, and dissipates the energy to the local environment as heat. Transfer of energy from triplet-state chlorophyll (in plants) or other porphyrins and proto-porphyrins (in mammals) to carotenoids occurs much more readily than the alternative energy transfer to oxygen to form the highly reactive and destructive singlet oxygen (¹O₂). Carotenoids may also accept the excitation energy from singlet oxygen if any should be formed in situ, and again dissipate the energy as heat.

The effect of carotenoids is different at high and low oxygen pressure, since they can quench oxygen physically and chemically. Carotenoids are able to quench singlet oxygen molecules physically, as the energy barrier between their ground and excited states is rather small, and decreases with increasing number of double bonds.

Carotenoids are also thought to have a variety of different actions, including possible antioxidant activity, immunoenhancement, inhibition of mutagenesis and transformation, inhibition of premalignant lesions, quenching of nonphotochemical fluorescence, and activity as a pigment in primate macula. These proposed actions are the subject of ongoing research but have not been established for γ-carotene specifically as distinct from the carotenoid class as a whole.

Biosynthetic Role in Plants

Carotenoids have an essential role in photosynthesis and at the same time they protect plants from overoxidation reaction catalyzed by chlorophylls by quenching singlet oxygen. Carotenoids also participate in different types of cell signaling. They are able to signal the production of abscisic acid, which regulates plant growth, seed dormancy, embryo maturation and germination, cell division and elongation, floral growth, and stress responses.

5. Scientific Evidence by Area of Use

Important caveat: Gamma-carotene has not been studied as an isolated compound in human clinical trials. The scientific evidence described below consists almost entirely of data from (a) studies of the carotenoid class as a whole, (b) studies primarily of β-carotene that include γ-carotene as a minor co-occurring compound in foods, or (c) in vitro or mechanistic data. There is currently no body of human clinical evidence specific to γ-carotene as an isolated supplement or therapeutic agent.

5.1 Provitamin A and Vision

The first sign of vitamin A deficiency is night blindness, or the inability to see in low light or darkness as a result of low rhodopsin levels in the retina. Xerophthalmia also affects the cornea and can eventually lead to permanent blindness; vitamin A deficiency is one of the top causes of preventable blindness in children.

Wald recognized that retinol was derived from carotenoids and that "the visual system expends vitamin A and is dependent upon diet for its replacement." Because γ-carotene contains the structural prerequisite β-ionone ring, it is theoretically capable of contributing to retinol status, but as stated, the bioconversion of γ-carotene to retinol has not been well-characterized. No clinical trials have administered isolated γ-carotene to humans to quantify its retinol equivalency in vivo.

Evidence strength: Indirect and theoretical. The provitamin A role is structurally plausible but not quantified for γ-carotene specifically in humans.

5.2 Antioxidant Effects and Chronic Disease

At present, it is unclear whether the biological effects of carotenoids in humans are related to their antioxidant activity and/or other non-antioxidant activities. Although the results of observational studies suggest that diets high in carotenoid-rich fruit and vegetables are associated with reduced risks of cardiovascular disease and some cancers, high-dose β-carotene supplements did not reduce the risk of cardiovascular disease or cancer in large randomized controlled trials.

Carotenoids are biologically active antioxidants, and their anti-inflammatory and antioxidant properties may help to lessen cardiovascular events such as adiposity, insulin sensitivity, hyperlipidemia, and inflammatory markers. These observations, however, derive from broader carotenoid research and not from γ-carotene-specific investigations.

Evidence strength: Class-level; no human evidence specific to γ-carotene.

5.3 Cancer Prevention

Two large-scale clinical trials — the Alpha-Tocopherol Beta-Carotene Cancer Prevention (ATBC) trial and the Carotene and Retinol Efficacy (CARET) trial — were prematurely terminated due to evidence of increased cancer risks in the β-carotene-only arm. These findings underscore that even for the well-studied β-carotene, supplementation at high doses carries risk rather than benefit in certain populations. Gamma-carotene has never been tested in a comparable human cancer prevention trial.

The pro-cancer effects in those trials might be attributed to high doses of synthetic β-carotene, as natural β-carotene, regardless of dosage, did not induce genotoxicity in preclinical models. Moreover, high doses of synthetic β-carotene exerted pro-oxidant activities under a free radical-rich environment, which may explain the results obtained in the ATBC and CARET clinical trials, as the participants of both trials were either smokers or asbestos-exposed workers, indicating their biological systems might have been under high oxidative stress for prolonged periods.

Carotenoids have been associated with various health effects: decreased risk of macular degeneration and cataracts, decreased risk of some cancers, and decreased risk of some cardiovascular events. These associations are observational and apply to dietary carotenoid patterns, not to γ-carotene supplementation specifically.

Evidence strength: No direct human evidence; associations are class-level and from observational data only.

5.4 Immune Function

Among the proposed biological actions of carotenoids is immunoenhancement. Both provitamin A and non-provitamin A carotenoids have been credited with other health-promoting effects, such as immuno-enhancement. Again, these observations pertain to the carotenoid class and are not specific to γ-carotene.

Evidence strength: No human evidence specific to γ-carotene.

5.5 Plasma Carotenoid Status and Survival Outcomes

One area of research has examined circulating total carotenoid levels as a biomarker of outcome, though not γ-carotene specifically. In a prospective study of head and neck squamous cell carcinoma patients, high levels of plasma carotenoids before radiotherapy were associated with prolonged progression-free survival (hazard rate ratio: 0.42, 95% CI: 0.20–0.91, p = 0.03). Seventy-eight HNSCC patients and 100 healthy controls were included. Dietary antioxidants (carotenoids, tocopherols, and ascorbic acid), ferric reducing antioxidant power (FRAP), and modified FRAP were lower in HNSCC patients compared to controls, and dietary antioxidants decreased during radiotherapy. γ-Carotene was not analyzed as an independent variable in this study.

Evidence strength: Observational only; γ-carotene not separately analyzed.

6. Body Systems and Health Areas Associated with Gamma-Carotene

Visual system / eye health: As a provitamin A carotenoid, γ-carotene is structurally capable of contributing to retinol supply necessary for rhodopsin synthesis and dark adaptation. To establish and sustain vision, animals have evolved pathways by which dietary chromophore precursors such as vitamin A and provitamin A are absorbed, transported, and metabolized to the chromophore. Night blindness, a condition that can be caused by an inadequate vitamin A supply to the eyes, is the oldest described eye disease known since ancient times.
Immune system: Via its potential conversion to retinol, γ-carotene may contribute to the immune functions dependent on vitamin A, including maintenance of mucosal barrier integrity. Chronic vitamin A deficiency has been associated with abnormal lung development, respiratory diseases, and an increased risk of anemia and death. Another effect is increased severity and mortality risk of infections, particularly measles and infection-associated diarrhea.
Skin and epithelial tissues: Vitamin A derived from provitamin A carotenoids plays a role in epithelial cell differentiation and maintenance.
Antioxidant defense: β-Carotene, α-carotene, zeaxanthin, β-cryptoxanthin, lutein, and lycopene have high antioxidant activity and promote free radical scavenging, which helps protect against chronic diseases. γ-Carotene, as a structurally similar carotene with a conjugated polyene chain, is expected to participate in the same general antioxidant mechanisms, though it has not been individually studied in this context in humans.

7. Dosage Forms and Reported Intakes

Dietary Exposure

Gamma-carotene is not commercially available as a standalone dietary supplement. It is encountered in the diet exclusively through food sources, where it occurs as a minor constituent of broader carotenoid profiles. Among the most abundant carotenoids in the North American diet are beta-carotene, alpha-carotene, gamma-carotene, lycopene, lutein, beta-cryptoxanthin, zeaxanthin, and astaxanthin.

Food-level concentrations that have been quantified by HPLC in peer-reviewed studies include: in pitanga (Eugenia uniflora) from Campinas, Brazil, (all-E)-γ-carotene was measured at approximately 3.8 μg/g fresh weight in ripe fruit, versus 1.6 μg/g in fruit from another growing region. In apricots, γ-carotene is present but subordinate to β-carotene, which accounts for 33–84% of total carotenoid content in studied cultivars.

Dietary intake of carotenoids varies widely across individuals and cultures. For example, the average intake of β-carotene is approximately 1.9 mg/day for Finnish populations but 17 mg/day for Fijian populations. Comparable population-specific data for γ-carotene intake specifically are not established in the published literature.

Supplement Forms

Gamma-carotene is not available as an isolated supplement in any established commercial or clinically studied form. It may appear in small quantities in mixed carotenoid supplements derived from natural plant or algal extracts, but its concentration in such products is not standardized or routinely disclosed. No human clinical trial has administered a defined dose of isolated γ-carotene, and therefore no clinically tested dosage range exists in the literature.

Bioavailability Considerations

Carotenoid bioavailability varies by cooking and processing of the food, as well as the amounts of dietary fat, fiber, and competing compounds in the meal. Upon ingestion, carotenoids are released from the food matrix and are emulsified with fat and incorporated into lipid micelles in the small intestine for absorption by intestinal enterocytes.

Pancreatic lipase, bile acids, fat, and possibly thyroid hormone aid in the absorption of carotene. Cooking, pureeing, or mashing fruits and vegetables ruptures cell membranes, thereby increasing the bioavailability of carotene for absorption. Absorption from foods is enhanced if eaten with fats, as carotenes are fat-soluble, and if the food is cooked for a few minutes until the plant cell wall splits and the color is released.

The use of carotenoids in the food industry is limited due to their poor solubility in water, bioavailability, and quick release. Encapsulation techniques, such as microencapsulation, nanoencapsulation, and supercritical encapsulation, are used to overcome these problems.

8. Safety Considerations and Interactions

General Safety of Dietary Carotenoids

Gamma-carotene consumed as part of whole foods is not associated with any known toxic effects. Despite carotenoid exposure being considered safe, markers of overexposure include clinical signs (i.e., carotenodermia, corneal rings, and retinopathy) and biochemical indicators (hypercarotenemia, xanthophyll esters).

Carotenodermia

Carotenodermia is reversible upon cessation of excessive intake. Consumption of greater than 30 mg/day for a prolonged period has been confirmed as leading to carotenemia. This data is established for β-carotene; direct thresholds for γ-carotene have not been established. The condition is a harmless yellowish-orange discoloration of the skin, most evident on palms and soles, and reverses when intake is reduced.

Pregnancy and Lactation

The safety of carotenoid supplements other than β-carotene in pregnancy and lactation has not been established, so pregnant and breastfeeding women should obtain carotenoids from food rather than supplements. There is no reason to limit the consumption of carotenoid-rich fruit and vegetables during pregnancy.

Drug Interactions and Absorption Modifiers

The cholesterol-lowering agents cholestyramine (Questran) and colestipol (Colestid) can reduce absorption of fat-soluble vitamins and carotenoids, as can mineral oil and Orlistat (Xenical), a drug used to treat obesity.

Just as dietary lipids enhance intestinal uptake of carotenoids, the consumption of unabsorbable, fat-soluble compounds may reduce carotenoid absorption. Carotenes — which include β-carotene, α-carotene, and lycopene, as well as other less-studied species — are unoxygenated terpenes.

Increasing gastric pH through the use of proton-pump inhibitors (Omeprazole, Lansoprazole) may decrease the absorption of a single dose of a β-carotene supplement, but the effect is unlikely to be clinically significant. This interaction has not been specifically studied for γ-carotene.

Pro-oxidant Risk at High Supplemental Doses

Lessons from high-dose β-carotene supplementation trials are relevant when considering any provitamin A carotenoid supplement. High doses of synthetic β-carotene exerted pro-oxidant activities under a free radical-rich environment. In the ATBC and CARET clinical trials, participants were either smokers or asbestos-exposed workers, indicating their biological systems might have been under high oxidative stress for prolonged periods. Whether analogous risks would apply to γ-carotene is unknown, as no equivalent trials have been conducted, but caution about high-dose isolated carotenoid supplementation is scientifically warranted.

Absence of a Tolerable Upper Intake Level

No tolerable upper intake level (UL) has been established for γ-carotene by any regulatory or scientific body (e.g., the Institute of Medicine/National Academies or EFSA), reflecting both the absence of documented toxicity and the absence of sufficient human dose-response data for this specific compound.

9. Research Gaps and Evidence Summary

Gamma-carotene occupies a scientifically understudied position within the carotenoid family. While its structural chemistry is well established, and its occurrence in specific foods has been quantified in peer-reviewed analytical studies, the following major gaps persist:

No human clinical trials have administered isolated γ-carotene at any dose.
The bioconversion efficiency of γ-carotene to retinol in humans has not been quantified (retinol activity equivalency has not been established for γ-carotene, in contrast to β-carotene and α-carotene).
Plasma pharmacokinetics and tissue distribution after dietary intake of γ-carotene have not been characterized in human volunteers.
No epidemiological studies have assessed γ-carotene intake separately from total carotenoid intake in relation to any disease outcome.
No standardized supplement preparation or dosage form exists for isolated γ-carotene.

At present, it is unclear whether the biological effects of carotenoids in humans are related to their antioxidant activity and/or other non-antioxidant activities. This uncertainty applies with even greater force to γ-carotene specifically, where the research base is far thinner than for β-carotene, lycopene, or lutein.

References

Health Conditions

Health conditions that Gamma-carotene may help support.

No conditions available.

Body Systems

Body systems that Gamma-carotene may help support.

No body systems available.