This review from 2000 covers important insights into the role of vitamin A in its multiple forms on physiology. Preformed vitamin A (all-trans-retinol and its esters) and provitamin A (beta-carotene) are essential dietary nutrients that provide a source of retinol. Both retinyl esters and beta-carotene are metabolized to retinol. The retinoid-binding proteins on binding retinol provide a means for solubilizing retinol for delivery to target tissues and for regulating retinol plasma concentrations. Oxidation of retinol provides retinal, which is essential for vision, and retinoic acid, a transcription factor ligand that has important roles in regulating genes involved in cell morphogenesis, differentiation and proliferation.
Dawson MI. The importance of vitamin A in nutrition. Curr Pharm Des. 2000 Feb;6(3):311-25. doi: 10.2174/1381612003401190. PMID: 10637381.