Retinyl palmitate

Biology

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. The esters are also intermediates in the visual cycle: RPE65 isomerizes the retinyl part to 11-cis-retinal.

Uses

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).

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.

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{{Cite journal | doi-access = free

Carcinogenicity controversy

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, fueling the sunscreen controversy in the popular press. One toxicological analysis determined that "there is no convincing evidence to support the notion that [retinyl palmitate] in sunscreens is carcinogenic." 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.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.

Teratogenicity

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." Preformed Vitamin A refers to retinyl palmitate and retinyl acetate.

References

References

1. (2014–2015). "[[CRC Handbook of Chemistry and Physics]]". CRC Press.
2. (July 2013). "Retinol and retinyl esters: biochemistry and physiology.". Journal of Lipid Research.
3. "The Top 300 of 2021".
4. "Vitamin A - Drug Usage Statistics".
5. [http://lpi.oregonstate.edu/infocenter/vitamins/vitaminA Vitamin A], Linus Pauling Institute
6. (1994). "Characterization of Esterase and Alcohol Dehydrogenase Activity in Skin. Metabolism of Retinyl Palmitate to Retinol (Vitamin A) During Percutaneous Absorption". Pharmaceutical Research.
7. (June 14, 2010). "Possible link between ingredient in sunscreen and skin cancer: Schumer". [[New York Daily News]].
8. (2010). "Safety of retinyl palmitate in sunscreens: a critical analysis.". Journal of the American Academy of Dermatology.
9. (1998). "Safe vitamin A dosage during pregnancy and lactation". [[World Health Organization]] (WHO).