Retinyl acetate (also called vitamin A acetate or allâÂÂtransâÂÂretinol acetate) is a synthetic, fatâÂÂsoluble retinyl ester often used to supply vitamin A in food fortification, dietary supplements, and topical cosmetic products.
Because the acetyl group protects the alcohol functionality, the compound is markedly more stable to heat, oxygen and light than free retinol, yet is rapidly hydrolyzed in the human intestine to active retinol after ingestion.
Commercially, retinyl acetate is the second most common retinyl ester after retinyl palmitate.
Retinyl acetate is the acetate ester of allâÂÂtransâÂÂretinol. Its polyene side chain makes the molecule highly lipophilic and sensitive to photoâÂÂoxidation; antioxidants (e.g., tocopherol) and opaque packaging are therefore used to limit degradation in finished products.
The compound melts at ~59â¯ðC and is practically insoluble in water but miscible with edible oils and most organic solvents.
Dietary retinyl acetate is hydrolyzed in the intestinal lumen by pancreatic triglyceride lipase and by brushâÂÂborder phospholipase B, releasing free retinol. The retinol is absorbed, reâÂÂesterified mainly with longâÂÂchain fatty acids by lecithinâÂÂretinol acyltransferase (LRAT) inside enterocytes, and secreted in chylomicrons to the liver, where 50âÂÂ80â¯% of totalâÂÂbody vitamin A is stored as retinyl palmitate in hepatic stellate cells. Mobilization of these stores releases retinol bound to retinolâÂÂbinding protein 4 (RBP4) for delivery to peripheral tissues.
LargeâÂÂscale vitamin A manufacture couples a C15 òâÂÂionone fragment with a C5 acetate side chain via a series of WittigâÂÂHorner and Grignard reactions, followed by final esterification or transâÂÂesterification to retinyl acetate. Modern processes achieve >95â¯% allâÂÂtrans selectivity and include crystallization or column purification under nitrogen to minimize isomerization.
The United States Food and Drug Administration lists retinyl acetate as "Generally Recognized as Safe" (GRAS) for use as a nutrient supplement in foods (21â¯CFRâ¯184.1930).
It is commonly added to margarine, plantâÂÂbased milk, breakfast cereals and staple oils in lowâ and middleâÂÂincome countries to prevent vitamin A deficiency.
Multivitamin tablets typically supply 600âÂÂ900â¯üg retinol activity equivalents (RAE) from retinyl acetate or retinyl palmitate. The U.S. National Institutes of Health sets a Tolerable Upper Intake Level (UL) of 3â¯000â¯üg RAEâ¯day<sup>âÂÂ1</sup> for adults.
Retinyl acetate is used in "antiâÂÂaging" skinâÂÂcare formulations as a milder, more photoâÂÂstable alternative to retinol. The EU Scientific Committee on Consumer Safety (SCCS) concluded in 2017, and reaffirmed in 2023, that leaveâÂÂon products are safe at concentrations providing up to 0.3â¯% retinol equivalents, while body lotions for children agedâ¯1âÂÂ3â¯years should not exceed 0.05â¯% retinol equivalents.
Excess preâÂÂformed vitamin A from supplements or fortified foods can cause hypervitaminosis A, characterized acutely by nausea and raised intracranial pressure and chronically by liver injury and teratogenicity.
Retinyl acetate shares these doseâÂÂdependent toxicities because it is quantitatively hydrolyzed to retinol. Phototoxicity and photoâÂÂisomerization are significantly lower than for unesterified retinol but can occur in formulations lacking UV stabilizers.