J Agric Food Chem. 2014 Jul 30;62(30):7559-66. Epub 2014 Jul 15.Pignitter M1, Dumhart B, Gartner S, Jirsa F, Steiger G, Kraemer K, Somoza V.Author information1Department of Nutritional and Physiological Chemistry and ‡Department of Inorganic Chemistry, University of Vienna , Vienna, Austria.AbstractOil fortification with retinyl palmitate is intended to lower the prevalence of vitamin A deficiency in populations at risk. Although the stability of vitamin A in vegetable oil has been shown to depend on environmental factors, very little information is known about the stability of vitamin A in preoxidized vegetable oils. The present study investigated the stability of retinyl palmitate in mildly oxidized (peroxide value < 2 mequiv O2/kg) and highly oxidized (peroxide value > 10 mequiv O2/kg) soybean oil stored under domestic and retail conditions. Soybean oil was filled in transparent bottles, which were exposed to cold fluorescent light at 22 or 32 °C for 56 days. Periodic oil sampling increased the headspace, thereby mimicking consumer handling.
Loss of retinyl palmitate in soybean oil by a maximum of 84.8 ± 5.76% was accompanied by a decrease of vitamin E by 53.3 ± 0.87% and by an increase of the peroxide value from 1.20 ± 0.004 to 24.3 ± 0.02 mequiv O2/kg. Fortification of highly oxidized oil with 31.6 IU/g retinyl palmitate led to a doubling of the average decrease of retinol per day compared to fortification of mildly oxidized oil. In conclusion, oil fortification programs need to consider the oxidative status of the oil used for retinyl palmitate fortification. PMID: 25003735 DOI: 10.1021/jf502109j [Indexed for MEDLINE] Publication typeResearch Support, Non-U.S. Gov'tMeSH termsAldehydes/chemistryCopper/chemistryFood Storage/methods*Food, Fortified*Soybean Oil/analysis*Tocopherols/chemistryVitamin A/analogs & derivatives*Vitamin A/chemistry*SubstancesAldehydesVitamin ATocopherolsretinol palmitateCopperSoybean Oiln-hexanalFull Text SourcesAmerican Chemical SocietyMedicalVitamin A - MedlinePlus Health InformationMiscellaneousHEXALDEHYDE - Hazardous Substances Data BankVITAMIN A - Hazardous Substances Data BankCOPPER, ELEMENTAL - Hazardous Substances Data BankSoybean oil - Hazardous Substances Data Bank
Skin benefits of retinol and retinyl palmitate Retinol and retinyl palmitate are among the most widely used active ingredients in skin care products. Unfortunately, there is much confusion about how they work, what results they can deliver and what their optimal usage is. This article will help clarify these issues. First, let me explain the basics. Both retinol and retinyl palmitate are forms of vitamin A (along with yet another form retinaldehyde). As opposed to many other vitamins, vitamin A does not have much of a direct biological effect. It works via its active metabolite (biochemical derivative) called retinoic acid. Only retinoic acid and its analogs collectively called retinoids have direct effect on skin cells and can adjust their physiology toward a more youthful state. In fact, retinoic acid a.k.a. tretinoin is the active ingredient in Retin A and Renova - some of the best-known anti-wrinkle creams (see our article on tretinoin). However, topical retinoic acid often causes skin irritation and other side effects, which limit its use, especially in sensitive individuals.
The good news is that skin cells have the "equipment" (specialized enzymes) converting various forms of vitamin A into retinoic acid. Indeed, if sufficient amounts of retinol, retinyl palmitate or retinaldehyde are added to the culture of skin cells, the amount of retinoic acid in the cells increases. Therefore, at least in theory, topical vitamin A may deliver at least some of the well-established skin benefits of retinoic acid while producing fewer side effects. Not all forms of vitamin A are created equal. Some are more easily converted to retinoic acid than others. A typical conversion pathway looks like this: It takes two and three metabolic steps, correspondingly, to convert retinol and retinyl palmitate to retinoic acid. The overall rate of conversion of retinol to retinoic acid is low and that of retinyl palmitate is lower still. Therefore a relatively large amount of retinol and even larger amount of retinyl palmitate needs to be delivered into a cell to boost retinoic acid levels and produce clinically meaningful effects.
Numerous products with retinol and retinyl palmitate are touted as equivalent to retinoic acid (tretinoin, Retin A) in effectiveness yet devoid of its side effects. The reality is a bit more complicated. Many of these products contain too little retinol / retinyl palmitate to have any noticeable effect. Simply the fact that these agents are in the list of ingredients is not enough. The products with high concentrations do exist but may still not deliver the purported benefits for a number of reasons. In particular, a product with highly concentrated retinol may cause skin irritation, especially in people with sensitive skin. Highly concentrated retinyl palmitate is less irritating than retinol (at equivalent levels) but is also less effective. (After all retinyl palmitate is the farthest away from retinoic acid in the metabolic pathway.) Furthermore, conversion rates of various forms of vitamin A to retinoic acid vary among individuals - the same product/concentration may yield visible benefits in some people and little or none in others.
Further still, retinol, and to a lesser degree retinyl palmitate, can be degraded by oxidation if formulated, stored and/or used improperly. Considering all these caveats, how should one use retinol / retinyl palmitate products (if at all)? As of the time of this writing, research indicates that the most reliable way to get all the skin rejuvenation benefits of retinoic acid is to actually use retinoic acid a.k.a. tretinoin (or other directly acting retinoids at optimal concentration. However, this may not be a viable option for some people. Retinoic acid and other directly acting retinoids require a prescription (at least in some countries) and are relatively expensive. They also tend to cause skin irritation, especially in sensitive individual or if used imprudently. The closest alternative is to use either topical retinaldehyde or retinyl retinoate (each of these agents is only one step away from retinoic acid). However, even though retinaldehyde creams do not require a prescription, they tend to be expensive and may still cause skin irritation whereas retinyl retinoate is a novel agent that is relatively untested and not easily available.
If for any of the above reasons retinoic acid (tretinoin, Retin A), retinaldehyde or retinyl retinoate are not suitable for you, a product with retinol and/or retinyl palmitate may be worth a try. When looking for such a product, it is important to find a stable, sufficiently concentrated formulation that does not irritate your skin. If commercial retinol/retinyl palmitate products prove too expensive or otherwise unsuitable for you, a do-it-yourself approach may help. It allows to easily customize retinol concentration to fit your skin physiology, i.e. you can adjust the concentration high enough to produce benefits but not so high as to cause irritation. Furthermore, if the DIY cream is used up soon after is has been prepared, retinol does not have time to degrade too much. For more on making your own retinol cream see DIY Anti-Aging Skin Care Infopack Despite the increasing availability of products containing various forms of vitamin A (retinoids precursors), retinoic acid a.k.a. tretinoin still offers a better chance of anti-wrinkle effects because its activity does not depend on conversion rates and other variables.