The vitamin A activity of beta-carotene.
In rats (parameters: growth, epithelial protection and liver storage), and in chicks (liver storage), it has been demonstrated that the conversion of beta-carotene to vitamin A diminishes inversely to the intake of beta-carotene, as long as the dosages are higher than 1-2 times the daily requirements. The decrease in the biopotency of beta-carotene follows a Michaelis Menten kinetic. In the dosage range of the daily requirements molecular ratio applies. Based on these findings, the following guidelines for the conversion of retinol in man are proposed: (Table: see text). For beta-carotene in oily solutions, a conversion factor of 1:3.33 should be accepted for the dosage range of 1,500 to 4,000 micrograms. For higher doses, this factor should be decreased according to the results with laboratory animals: For beta-carotene in vegetables, the conversion factor of 1:6.0 should be accepted for intakes between 1,500 and 4,000 micrograms. A higher factor should be chosen for smaller intakes, and a smaller factor for higher intakes.
D000818:Animals; D001681:Biological Assay; D002338:Carotenoids / Q000008:administration & dosage* / Q000378:metabolism; D002645:Chickens; D004224:Diterpenes; D004305:Dose-Response Relationship, Drug; D004848:Epithelium / Q000187:drug effects; D005260:Female; D006128:Growth; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D051381:Rats; D000084562:Retinyl Esters; D014621:Vagina / Q000187:drug effects; D014801:Vitamin A / Q000008:administration & dosage* / Q000031:analogs & derivatives / Q000378:metabolism; D019207:beta Carotene
D004224:Diterpenes; D000084562:Retinyl Esters; D019207:beta Carotene; D014801:Vitamin A; D002338:Carotenoids; C009166:retinol acetate