Community hub
0 subscribers8 pages, 0 posts
Recent from talks
All channels
Be the first to start a discussion here.
Be the first to start a discussion here.
Be the first to start a discussion here.
Be the first to start a discussion here.
Contribute something
Welcome to the community hub built to collect knowledge and have discussions related to Retinyl palmitate.
Nothing was collected or created yet.
Retinyl palmitate
View on Wikipediafrom Wikipedia
 | |||
| |||
| Names | |||
|---|---|---|---|
| IUPAC name
Retinyl hexadecanoate
| |||
| Systematic IUPAC name
(2E,4E,6E,8E)-3,7-Dimethyl-9-(2,6,6-trimethylcyclohex-1-en-1-yl)nona-2,4,6,8-tetraen-1-yl hexadecanoate | |||
| Other names
Retinol palmitate
| |||
| Identifiers | |||
3D model (JSmol)
|
|||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider | |||
| ECHA InfoCard | 100.001.117 | ||
| KEGG | |||
PubChem CID
|
|||
| UNII | |||
CompTox Dashboard (EPA)
|
|||
| |||
| |||
| Properties | |||
| C36H60O2 | |||
| Molar mass | 524.86 g/mol | ||
| In water, ethanol and ethers[1] | |||
| Hazards | |||
| NFPA 704 (fire diamond) | |||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |||
Retinyl palmitate, or vitamin A palmitate, is the ester of retinol (vitamin A) and palmitic acid, with formula C36H60O2. It is the most abundant form of vitamin A storage in animals.[2]
An alternate spelling, retinol palmitate, which violates the -yl organic chemical naming convention for esters, is also frequently seen.[citation needed]
In 2021, vitamin A was the 298th most commonly prescribed medication in the United States, with more than 500,000 prescriptions.[3][4]
Biology
[edit]Animals use long-chain esters of vitamin A, most abundantly the palmitate form, as a form of vitamin A storage. The storage reaction is catalyzed by LRAT, and the inverse is catalyzed by REH.[2] The esters are also intermediates in the visual cycle: RPE65 isomerizes the retinyl part to 11-cis-retinal.[2]
Uses
[edit]Vitamin A palmitate is a common vitamin supplement, available in both oral and injectable forms for treatment of vitamin A deficiency, under the brand names Aquasol A, Palmitate A, and many others. It is a constituent of intraocular treatment for dry eyes at a concentration of 138 μg/g (VitA-Pos) by Ursapharm. It is a pre-formed version of vitamin A; therefore, the intake should not exceed the Recommended Dietary Allowance (RDA). Overdosing on preformed Vitamin A forms, such as retinyl palmitate, leads to adverse physiological reactions (hypervitaminosis A).[5]
Retinyl palmitate is used as a source of vitamin A added to low-fat milk and other dairy products to replace the vitamin content lost through the removal of milk fat. Palmitate is attached to the alcohol form of vitamin A, retinol, to make vitamin A stable in milk.[citation needed]
Retinyl palmitate is also a constituent of some topically applied skin care products. After its absorption into the skin, retinyl palmitate is converted to retinol, and ultimately to retinoic acid (the active form of vitamin A present in Retin-A), though neither its skin absorption[6] nor its conversion[7] is very effective.
Carcinogenicity controversy
[edit]New York Senator Chuck Schumer has called attention to the fact that high doses of topical retinyl palmitate were shown to accelerate cancer in lab animals,[8] fueling the sunscreen controversy in the popular press.[9] One toxicological analysis determined that "there is no convincing evidence to support the notion that [retinyl palmitate] in sunscreens is carcinogenic."[9] A technical report issued thereafter by the National Toxicology Program concluded that diisopropyl adipate increased the incidence of skin tumors in mice, and the addition of either retinoic acid or retinyl palmitate both exacerbated the rate and frequency of tumors.[10]
Teratogenicity
[edit]World Health Organization recommendation on Maternal Supplementation During Pregnancy states that "health benefits are expected for the mother and her developing fetus with little risk of detriment to either, from a daily supplement not exceeding 10,000 IU [preformed] vitamin A (3000 μg RE) at any time during pregnancy."[11] Preformed Vitamin A refers to retinyl palmitate and retinyl acetate.[citation needed]
See also
[edit]References
[edit]- ^ William M. Haynes (2014–2015). CRC Handbook of Chemistry and Physics (95th ed.). CRC Press. p. 622. ISBN 978-1-4822-08672..
- ^ a b c O'Byrne, SM; Blaner, WS (July 2013). "Retinol and retinyl esters: biochemistry and physiology". Journal of Lipid Research. 54 (7): 1731–43. doi:10.1194/jlr.R037648. PMC 3679378. PMID 23625372.
- ^ "The Top 300 of 2021". ClinCalc. Archived from the original on 15 January 2024. Retrieved 14 January 2024.
- ^ "Vitamin A - Drug Usage Statistics". ClinCalc. Retrieved 14 January 2024.
- ^ Vitamin A, Linus Pauling Institute
- ^ E. A. Duell, S. Kang & J. J. Voorhees (1997). "Unoccluded retinol penetrates human skin in vivo more effectively than unoccluded retinyl palmitate or retinoic acid". The Journal of Investigative Dermatology. 109 (3): 301–305. doi:10.1111/1523-1747.ep12335788. PMID 9284094.
- ^ Boehnlein, James; Sakr, Adel; Lichtin, J. Leon; Bronaugh, Robert L. (1994). "Characterization of Esterase and Alcohol Dehydrogenase Activity in Skin. Metabolism of Retinyl Palmitate to Retinol (Vitamin A) During Percutaneous Absorption". Pharmaceutical Research. 11 (8): 1155–1159. doi:10.1023/A:1018941016563. ISSN 0724-8741. PMID 7971717. S2CID 25458156.
- ^ "Possible link between ingredient in sunscreen and skin cancer: Schumer". New York Daily News. June 14, 2010.
- ^ a b Wang, SQ; Dusza, SW; Lim, HW (2010). "Safety of retinyl palmitate in sunscreens: a critical analysis". Journal of the American Academy of Dermatology. 63 (5): 903–6. doi:10.1016/j.jaad.2010.07.015. PMID 20692724.
- ^ National Toxicology Program. (2012). NTP technical report on the photocarcinogenesis study of retinoic acid and retinyl palmitate [CAS Nos. 302-79-4 (All-trans-retinoic acid) and 79-81-2 (All-trans-retinyl palmitate)] in SKH-1 mice (Simulated solar light and topical application study). Available at https://ntp.niehs.nih.gov/sites/default/files/ntp/htdocs/lt_rpts/tr568_508.pdf. Accessed September 19, 2013.
- ^ Safe vitamin A dosage during pregnancy and lactation (PDF), World Health Organization (WHO), 1998.
Retinyl palmitate
View on Grokipediafrom Grokipedia
Chemical Properties
Molecular Structure and Synthesis
Retinyl palmitate is the ester derived from all-trans-retinol, the primary alcohol form of vitamin A, and palmitic acid, a saturated straight-chain fatty acid with 16 carbon atoms (hexadecanoic acid).[10] Its molecular formula is CHO, with a molecular weight of 524.86 g/mol.[10] The core structure features a β-ionone cyclohexene ring connected via a tetraene polyene side chain to the C-15 hydroxyl group of retinol, which is esterified to the carboxyl group of palmitic acid, enhancing its lipophilicity and stability compared to free retinol.[11] Synthesis of retinyl palmitate typically involves direct esterification of retinol with palmitoyl chloride in an anhydrous solvent under basic conditions, such as with pyridine or triethylamine, to form the ester bond while minimizing isomerization or degradation of the sensitive polyene chain.[12] Alternative methods include transesterification of retinyl acetate with methyl palmitate catalyzed by sodium methoxide or enzymatic approaches using lipases in non-aqueous media, which offer higher selectivity and milder conditions to preserve the all-trans configuration.[13] [14] Industrial production predominantly relies on synthetic retinol, synthesized from β-ionone and propargyl derivatives through multi-step processes optimized since the 1940s by firms like Roche, followed by esterification to yield retinyl palmitate in oil-dispersible forms with purity exceeding 90%.[15] [16] Natural-derived versions can be isolated from fish liver oils, where retinyl palmitate occurs as the predominant storage ester, but chemical synthesis ensures consistent potency, often standardized to 1.5–1.7 million international units (IU) of vitamin A activity per gram in commercial preparations.[17]Physical and Stability Characteristics
Retinyl palmitate is a yellow to orange-brown viscous oil at room temperature.[18] Its lipophilic nature results in insolubility in water, with solubility below 0.0001 mg/L, while it dissolves readily in organic solvents including chloroform, diethyl ether, and vegetable oils such as corn oil.[18][17] The compound has a melting point of approximately 28°C, existing as a liquid under ambient conditions but solidifying upon cooling.[10][19] The esterification of retinol with palmitic acid imparts greater chemical stability to retinyl palmitate relative to free retinol, particularly against oxidation and environmental stressors, thereby extending shelf life in storage and formulation contexts.[20] Nonetheless, it degrades under exposure to light, heat, and oxidants, with photodegradation accelerated by ultraviolet irradiation leading to loss of vitamin A activity.[21][22] Antioxidants such as butylated hydroxytoluene can mitigate light- and heat-induced degradation across various pH levels.[21] The ester bond permits hydrolysis under acidic, basic, or enzymatic conditions, yielding retinol and palmitic acid.[17] Spectroscopically, retinyl palmitate absorbs ultraviolet light with a maximum wavelength near 325 nm, a property shared with other retinoids and exploited in high-performance liquid chromatography with UV detection for quantitative analysis.[23][24] This absorption profile aids in monitoring stability and purity during handling.[25]
Biological Role
Metabolism and Physiological Functions
Retinyl palmitate, primarily obtained from animal-derived foods or supplements, is hydrolyzed in the intestinal lumen and enterocytes by pancreatic and brush-border retinyl ester hydrolases to release free retinol for absorption. Within enterocytes, retinol is re-esterified mainly to retinyl palmitate by enzymes such as lecithin:retinol acyltransferase (LRAT), incorporated into chylomicrons, and transported via lymph to the liver for storage in hepatic stellate cells as retinyl esters.[26][27][28] In the liver, stored retinyl esters maintain vitamin A homeostasis; during periods of dietary insufficiency or increased demand, they are mobilized by hydrolases like PNPLA3, yielding retinol that complexes with retinol-binding protein (RBP) and transthyretin for delivery to peripheral tissues. There, retinol is oxidized stepwise—first to retinal by short-chain dehydrogenases/reductases or alcohol dehydrogenases, then to retinoic acid by retinal dehydrogenases—to serve as ligands for nuclear receptors regulating gene transcription.[29][28][30] These conversions enable retinyl palmitate's contributions to key physiological processes as a vitamin A reservoir. Retinal supports phototransduction in vision by binding opsins to form rhodopsin in photoreceptor cells, while retinoic acid drives epithelial cell differentiation, mucociliary clearance in respiratory tracts, and spermatogenesis in reproduction. Vitamin A also bolsters innate and adaptive immunity by promoting T-cell differentiation and antibody production; depletion of retinyl ester stores leads to xerophthalmia, night blindness, and heightened infection risk due to impaired barrier integrity and immune surveillance.[5][31][32] Bioavailability of retinyl palmitate exceeds that of provitamin A carotenoids, with preformed esters absorbed at 70–90% efficiency versus 20–50% for plant-derived carotenoids, owing to direct hydrolysis and uptake without requiring cleavage enzymes; this advantage is pronounced in supplements, where micellar solubilization enhances intestinal uptake over complex food matrices.[33][31][34]Essentiality as Vitamin A Precursor
Retinyl palmitate, an ester of retinol and palmitic acid, functions as a storage and transport form of preformed vitamin A in the body, where it is hydrolyzed by enzymes such as retinyl ester hydrolases to yield retinol, the biologically active alcohol form essential for human health.[5] Humans cannot synthesize vitamin A endogenously and must obtain it through dietary sources, with retinyl palmitate providing retinol activity equivalents (RAE) on a 1:1 molar basis after hydrolysis, equivalent to 1 mcg RAE per mcg of retinol derived.[5] The recommended dietary allowance (RDA) for vitamin A, expressed in RAE, is 900 mcg per day for adult males and 700 mcg per day for adult females, underscoring the quantitative necessity of preformed sources like retinyl palmitate to meet these requirements in populations with limited provitamin A carotenoid intake.[5][35] Deficiency in vitamin A, which can be mitigated by retinyl palmitate supplementation, leads to severe outcomes including xerophthalmia, impaired growth, and increased susceptibility to infections, with global data indicating that supplementation in deficient children aged 6 months to 5 years reduces all-cause mortality, diarrhea incidence, and measles risk.[36] Clinical trials in vitamin A-deficient regions have demonstrated mortality reductions of 12–24% attributable to periodic high-dose supplementation, preventing an estimated 600,000 child deaths annually if scaled to 190 million at-risk children based on 2008 prevalence data.[37] These effects stem from vitamin A's role in maintaining epithelial integrity and immune competence, where retinol-derived metabolites support T-cell differentiation and antibody production.[38] At the molecular level, retinol from retinyl palmitate is oxidized to retinal and then to retinoic acid, which binds nuclear retinoic acid receptors (RARs) and retinoid X receptors (RXRs) to regulate gene transcription critical for embryonic development, spermatogenesis, ovarian function, and somatic growth.[39][40] RAR activation promotes cellular differentiation and proliferation in tissues such as the skin, lungs, and reproductive organs, while also modulating antioxidant defenses against oxidative stress, thereby linking vitamin A essentiality to reproduction and longitudinal bone growth via insulin-like growth factor pathways.[2][41] Inadequate intake disrupts these pathways, as evidenced by animal models and human deficiency states showing halted growth and infertility reversible only by retinol repletion.[42]Applications
In Cosmetics and Skincare
Retinyl palmitate serves as a stable precursor to retinol in topical cosmetic formulations, primarily anti-aging creams, moisturizers, and serums, where it is included at concentrations ranging from 0.05% to 1% to promote gradual skin cell turnover and collagen synthesis.[8][43] As an ester of retinol and palmitic acid, it requires enzymatic hydrolysis in the skin to yield active retinol, resulting in a slower onset of effects compared to direct retinoic acid application, which aligns with its use for mild, sustained retinoid activity without the potency of prescription tretinoin.[44] These products have been available over-the-counter since the 1980s, following early recognition of retinoids' role in addressing photoaged skin.[43] Its incorporation into oil-soluble phases enhances formulation stability, as retinyl palmitate resists oxidation better than free retinol, maintaining efficacy over product shelf life under proper storage conditions below 20°C.[45][20] This stability allows blending into emulsions without rapid degradation, and clinical assessments indicate lower irritation potential than retinol, with reduced erythema in patch tests at equivalent retinoid-equivalent doses.[46][47] Empirical data from randomized controlled trials support modest improvements in skin parameters, such as enhanced epidermal thickness and reduced fine wrinkles, attributed to upregulated fibrillin-1 expression and antioxidant pathways in photoaged skin models.[48][44] For instance, applications in gel formulations have shown visible texture refinement after 8-12 weeks, though retinyl palmitate's weaker potency—requiring 3-5 times higher concentrations than retinol for comparable activity—limits it to supportive roles in regimens rather than standalone transformation.[49][50]In Nutritional Supplements and Fortification
Retinyl palmitate is widely employed as a stable preformed vitamin A source in oral nutritional supplements, including multivitamins, and in food fortification programs targeting populations at risk of deficiency, owing to its greater resistance to oxidation and degradation compared to retinol during storage and processing.[51] It is commonly added to vegetable oils, cereals, dairy products like milk, and spreads such as margarine to enhance vitamin A content without compromising product stability.[25][52] In public health initiatives, retinyl palmitate or equivalent esters form the basis of supplementation protocols, such as India's National Prophylaxis Programme against Nutritional Blindness, launched in 1970 to deliver mega-doses (typically 200,000 IU for children aged 1-5 years, administered biannually) aimed at preventing xerophthalmia and related corneal damage from vitamin A deficiency.[53] Similar programs in developing regions utilize it for periodic dosing to address subclinical deficiencies, with treatment regimens for confirmed cases involving initial oral doses of 100,000-200,000 IU daily for 3 days, followed by 50,000 IU daily for up to 2 weeks, then maintenance via diet or lower-dose supplements.[5][54] Bioavailability studies indicate that retinyl palmitate in oil-based vehicles achieves efficient intestinal absorption, with hydrolysis to retinol yielding plasma responses comparable to other preformed vitamin A forms, supporting its utility in fortificants like edible oils where fat enhances uptake.[55] Randomized controlled trials in deficient populations of developing countries, including meta-analyses of community-based interventions, demonstrate that such supplementation reduces all-cause child mortality by 12-24%, alongside lowering incidences of diarrhea, measles, and respiratory infections through bolstered immune function and epithelial integrity.[36][56] These effects are attributed to correcting marginal deficiencies that impair adaptive immunity, as evidenced by decreased morbidity in trials across Asia and Africa.[57]Industrial and Pharmaceutical Uses
Retinyl palmitate is incorporated into animal feeds as a stable vitamin A source to support livestock nutrition, growth promotion, and reproductive health. The European Food Safety Authority assessed retinyl palmitate alongside other retinyl esters as a feed additive for all animal species, affirming its efficacy in delivering bioavailable vitamin A without adverse effects on animal performance or environmental safety when used at authorized levels up to 50,000 IU/kg complete feed for most categories.[58] In the United States, vitamin A palmitate holds generally recognized as safe (GRAS) status for animal feed applications under good manufacturing and feeding practices, enabling its use in premixes for poultry, swine, and ruminants to prevent deficiencies that impair weight gain and immunity.[59] Neonatal supplementation with vitamin A forms, convertible from retinyl palmitate, has demonstrated enhanced muscle hypertrophy in calves through upregulated myogenesis and satellite cell proliferation, contributing to improved carcass yield in beef production.[60] In pharmaceutical manufacturing, retinyl palmitate functions primarily as a reference standard for chromatographic assays ensuring vitamin A potency in drug formulations, with its ester stability aiding quality control over free retinol's volatility.[61] It appears in select oral and injectable retinoid preparations as an adjunct for conditions involving vitamin A deficits, though synthetic retinoids like etretinate predominate in dermatological treatments for acne or psoriasis due to targeted receptor activity; retinyl palmitate's broader metabolic conversion limits its specificity in oncology supports.[62] Laboratory research employs retinyl palmitate as a less oxidizable vitamin A depot in cell culture media for studying retinoid signaling in proliferation and differentiation, such as in keratinocyte models of UV stress or microbial production systems optimizing ester yields for downstream applications.[63] Its use remains ancillary compared to cosmetics, with formulations prioritizing encapsulation to mitigate hydrolysis in aqueous environments.[64]Safety and Toxicology
Acute and Chronic Toxicity Profiles
Retinyl palmitate exhibits low acute oral toxicity, with an LD50 greater than 2,000 mg/kg body weight in rats, indicating it is practically nontoxic in single high-dose administrations.[65][66] Specific studies report an LD50 of approximately 7,910 mg/kg in rats, while values around 6,060 mg/kg have been observed in mice.[67] At excessive single doses, symptoms may include nausea, vomiting, and vertigo, consistent with general vitamin A acute overdose effects, though retinyl palmitate's ester form results in slower absorption compared to free retinol, potentially mitigating immediate severity.[65] In chronic toxicity assessments, no-observed-adverse-effect levels (NOAELs) for retinyl palmitate, as a preformed vitamin A source, align with broader vitamin A data, showing safety margins in animal models at elevated intakes. Dogs tolerated dietary vitamin A concentrations up to 100,000 IU per 1,000 kcal metabolizable energy without adverse effects in growth and organ histology studies spanning months.[68] Hypervitaminosis A from prolonged excess preformed vitamin A, including retinyl palmitate, manifests as liver fibrosis, bone abnormalities, and skin changes, typically requiring daily intakes exceeding 25,000 IU (7,500 mcg retinol activity equivalents) for months to years.[69] Retinyl palmitate's lower bioavailability relative to retinol—due to enzymatic hydrolysis requirements—delays toxicity onset, with ester forms showing reduced potency in dose-response curves.[8] Human epidemiological and clinical data support safe chronic intake up to the tolerable upper limit of 3,000 mcg retinol activity equivalents per day from preformed sources like retinyl palmitate, with no widespread toxicity in populations adhering to this threshold.[70] Claims of broad toxicity often lack context of underlying deficiency correction or exceedance of this limit, as longitudinal studies refute adverse effects at recommended supplemental levels absent predisposing factors like liver impairment.[5] Chronic excesses beyond 8,000-10,000 mcg RAE daily elevate plasma retinyl esters, correlating with hepatic risks, but retinyl palmitate supplementation within guidelines shows no such associations in healthy adults.[71][31]Reproductive and Developmental Effects
Retinyl palmitate, a storage form of preformed vitamin A, exerts reproductive and developmental effects primarily through its enzymatic hydrolysis to retinol and subsequent conversion to retinoic acid, which modulates gene expression via retinoic acid receptors during embryogenesis. Excess retinoic acid disrupts anterior-posterior patterning and neural crest cell migration, potentially causing craniofacial dysmorphias (e.g., microtia, cleft palate), cardiac anomalies, and central nervous system defects in animal models.[72] This mechanism underlies the teratogenic potential observed with high doses of preformed vitamin A esters, though retinyl palmitate demonstrates lower potency than free all-trans-retinoic acid due to slower bioavailability.[73] In rodent studies, oral administration of retinyl palmitate at doses exceeding 100 mg/kg body weight on gestational day 10 induced dose-dependent teratogenicity, including visceral and skeletal malformations, alongside maternal toxicity such as reduced weight gain.[74] However, chronic exposure to high dietary levels (up to 27.5 mg/kg/day, equivalent to approximately 50,000 IU/kg) in rats produced no fetal malformations, indicating a threshold effect where ester hydrolysis limits peak retinoic acid concentrations.[75] Single doses around 15,000 IU/kg via injection showed minimal teratogenic outcomes unless repeated, further distinguishing retinyl palmitate's profile from more bioavailable retinoids like 13-cis-retinoic acid.[8] Human evidence links preformed vitamin A intakes above 10,000 IU/day (3,000 mcg retinol equivalents) during early pregnancy to elevated birth defect risks, with cohort studies reporting odds ratios of 2.5–4.8 for craniofacial and cardiac anomalies in cases exceeding 25,000 IU/day.[76] Teratogenic incidents remain rare (<20 documented over decades), typically involving chronic supplementation abuse rather than standard retinyl palmitate use, and no specific epidemiological data isolates retinyl palmitate from other preformed sources.[77] Meta-analyses of vitamin A supplementation trials find no significant association with congenital malformations at doses below 5,000 IU/day, supporting safety within recommended limits.[72] Regulatory guidance reflects this dose-dependent risk: the UK Committee on Toxicity and EFSA recommend pregnant women limit preformed vitamin A to ≤10,000 IU/day to avoid exceeding thresholds where fetal signaling disruption becomes probable, while emphasizing that dietary esters like retinyl palmitate rarely attain teratogenic levels without intentional excess. WHO concurs, deeming up to 10,000 IU/day safe for non-deficient populations, with beta-carotene forms preferred over esters for supplementation to minimize preformed intake variability.[78]Photocarcinogenicity and UV Interaction Studies
National Toxicology Program (NTP) studies conducted in the early 2000s and culminating in Technical Report 568 (published 2010) examined the photocarcinogenic potential of topical retinyl palmitate (RP) in SKH-1 hairless mice exposed to simulated solar light (SSL).[79] In these experiments, female SKH-1 mice received topical applications of RP (0.1% to 0.5% concentrations) in a cream vehicle following SSL doses of 6.85 mJ·CIE/cm² five days per week for up to 40 weeks, with RP enhancing tumor development compared to vehicle controls.[6] Papilloma incidence reached 95.9% in the 0.5% RP group versus 44.4% in controls, with multiplicity increasing to 11.70 tumors per mouse versus 6.76 (p < 0.001); latency shortened to 107-167 days versus 260 days.[6] Similar trends occurred for squamous cell carcinomas, with earlier onset and higher multiplicities attributed to RP photodegradation yielding reactive oxygen species and lipid peroxides acting as pro-oxidants.[80][6] Countervailing evidence challenges direct extrapolation to humans. RP demonstrated no genotoxicity in Chinese hamster ovary (CHO) cells, even under pre- or simultaneous UV irradiation, in assays evaluating chromosomal aberrations and sister chromatid exchanges.[81] Human epidemiological data and short-term trials reveal no elevated skin cancer risk from topical RP with UV exposure, contrasting mouse outcomes where SKH-1 strains exhibit heightened UV sensitivity—developing tumors after minimal dosing irrelevant to human thresholds—and vehicle components like diisopropyl adipate provoke greater irritation in rodents than people.00850-9/abstract)[8] Empirical limitations persist, including the absence of long-term randomized controlled trials in humans assessing RP-UV interactions causally. Vitamin A derivatives like RP exhibit context-dependent duality—antioxidant at physiological levels but potentially pro-oxidant via UV-induced breakdown—yet no mechanistic or observational data establish photocarcinogenic causality in human skin, underscoring reliance on animal models with limited translatability.00850-9/abstract)[80]Regulatory Status and Controversies
Global Regulatory Approvals and Limits
Retinyl palmitate is affirmed as generally recognized as safe (GRAS) by the U.S. Food and Drug Administration (FDA) for use as a direct food additive in conventional foods, with specifications including its preparation as the palmitate ester of retinol under 21 CFR 184.1930.[82] The Cosmetic Ingredient Review (CIR) Expert Panel has concluded that retinyl palmitate is safe for use as a cosmetic ingredient in concentrations reflecting current practices, typically up to 1% in topical formulations, based on assessments of irritation, sensitization, and systemic exposure risks.[8][83] In the European Union, the Scientific Committee on Consumer Safety (SCCS) issued a revised opinion on October 26, 2022, deeming vitamin A forms including retinyl palmitate safe in cosmetics at maximum concentrations of 0.05% retinol equivalents (RE) in body lotions and 0.3% RE in other leave-on and rinse-off products, accounting for aggregate exposure from diet and supplements.[9] These limits were codified in Commission Regulation (EU) 2024/996, effective May 2025, adding entries for retinol, retinyl acetate, and retinyl palmitate to Annex III of the Cosmetics Regulation, with requirements for labeling warnings on potential skin irritation.[84] No outright bans exist, despite advocacy from groups like the Environmental Working Group citing precautionary concerns from animal models, as regulators have emphasized human exposure data and margins of safety in approvals.[85] The World Health Organization (WHO) endorses retinyl palmitate in high-dose oral supplements for preventing vitamin A deficiency in children aged 6–59 months in at-risk populations, recommending 100,000–200,000 IU doses every 4–6 months as retinyl palmitate or acetate in oil-based formulations.[86] For postpartum women in deficiency-prevalent areas, WHO guidelines support supplementation with up to 200,000 IU shortly after delivery, prioritizing deficiency correction over unverified low-level risks.[87] Regulatory variations include enhanced pregnancy advisories for supplements containing retinyl palmitate, with authorities like the FDA and teratogen information services warning against doses exceeding 10,000 IU daily due to associations with birth defects, though food and cosmetic uses remain unrestricted beyond general limits.[88][89] No jurisdiction imposes sunscreen-specific prohibitions, with EU assessments confirming safety within the broader cosmetic concentration caps.[9]| Jurisdiction | Food/Supplement Status | Cosmetic Limits |
|---|---|---|
| United States (FDA/CIR) | GRAS for food; approved in OTC drugs | Safe as used (up to ~1% topical)[82][8] |
| European Union (SCCS/Annex III) | Not restricted beyond general vitamin A intake guidelines | 0.05% RE (body lotions); 0.3% RE (other products)[9][84] |
| WHO (Global) | Endorsed for deficiency supplementation (e.g., 100,000–200,000 IU doses) | N/A[86] |