Retinol bioavailability

Tanumihardjo SA. 2002. Factors influencing the conversion of carotenoids to retinol bioavailability to bioconversion to bioefficacy. Int J Vitam Nutr Res 72 40-5. 

Figure 2 A schematic outlining the path of /3-carotene (/3-C) as it moves out from the food into the intestinal wall. The definition of terms associated with understanding /3-carotene release, absorption, and conversion to retinoi are iiiustrated bioaccessibility, bioavailability, bionconversion, and bioefficacy. (Reproduced with permission from Tanumihardjo SA (2002) Factors influencing the conversion of carotenoids to retinol Bioavailability to bioconversion to bioefficacy. International Journal of Vitamin and Nutrition Research 72 40-45.)...

Carotene (all-trans), (3-cryptoxanthin (all-trans and -cis), zeaxanthin (all-trans), luteoxanthin isomers, violaxanthin (all-trans and -cis), and neoxanthin (all-trans and -cis) were identified in several mango cultivars (Mercadante and others 1997 Ornelas-Paz and others 2007, 2008). Mango retinol was found to be highly bioavail-able by estimating vitamin A and carotene reserves in the liver and plasma of rats. Information on the tocopherol content in mango is very scarce, but it seems to be low (Burns and others 2003 Ornelas-Paz and others 2007). 

Since the IU was based on studies that did not take into account the poor absorption and bioavailability of carotenoids in foods, the equivalency of retinol and /3-carotene in the IU system differs from that in the RE system. Thus in the RE system, 1 fig retinol = 6 fig /3-carotene, whereas in the IU system, 1 fig retinol = 2 fig /3-carotene. 

Wang, Y. Xu, X. van Lieshout, M. West, C.E. Lugtenburg, J. Verhoeven, M.A. Creemers, A.F.L. Muhilal and van Breemen, R.B. 2000. A liquid chromatography-mass spectrometry method for the quantification of bioavailability and bioconversion of P-carotene to retinol in humans. Anal. Chem. 72 4999-5003. 

Retinol induces the expression of retinoic acid-binding protein (RABP) and regulates cell migration in the skin epithelium, which is vital for skin regeneration after a peel. Encapsulating retinol provides better bioavailability of the vitamin and protects the skin against oxidation. Ker-atinocytes have the enzyme tools required to convert retinol into retinoic acid (the corresponding carboxylic acid), which is the molecule ultimately responsible for the effect of vitamin A. 

Retinoic acid regulates the transcription of genes that code for the synthesis of important intracellular proteins. Retinol also induces the expression of the protein that transports retinoic acid. Retinol encapsulated in cyclodextrins (Renutriv ACE Lipoic Complex -SkinTech) has greater bioavailability and its antioxidant action is of better quality. 

Many active principles of interest in cosmetics were complexed with cyclodextrins. achieving positive and interesting results. For instance, the inclusion of retinol in hydroxypropyl-P-cyclodextrin leads to a water-soluble product, sufficiently stable, of higher bioavailability and lower toxicity compared to free retinol. Similarly, it is possible to include almost all vitamins in cyclodextrins. with unquestionable advantages with regard to their... 

The use of cyclodextrins in the cosmetic industry is very similarly widespread. Most vitamins form stable complexes with cyclodextrins. These complexes have been found to increase the bioavailability of compounds such as vitamin A and retinol. The added advantage is the protection of vifamin A and retinol against oxidation. Again, as with the food indusfry, emulsions are easily prepared. Cyclodextrins have also been incorporated into many sun-block lotions. Complex-ation increases the photostability of the cream, increases its protective properties, reduces odour and decreases the staining of fabrics. 

On the base of this observation it can be said that retinyl-palmitate might be used instead of retinol in pharmaceutical preparations, because the bioavailability of retinyl-palmitate as compared to that of retinol is independent of the oil and the fat in which it has been dissolved. 

Because many factors affect the assimilation of carotenoids from foods (Figure 2), conversion factors need to be considered. This is especially important when most sources of vitamin A are from provitamin A carotenoids in the population. Bioavailability of preformed vitamin A, i.e., retinol and retinyl esters, is not a major concern because 80-95% of them are absorbed. However, foods that are high in preformed retinol (liver, eggs, and fortified milk) are not necessarily consumed by everybody. When discussing carotenoids from food, four terms need to be defined (see Table 1) ... 

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