Vitamin A

Vitamin A is a generic name for a group of fat-soluble compounds that include retinol, retinal, and retinoic acid, collectively known as retinoids. It is not a therapeutic target (such as a receptor, enzyme, or transporter) but an essential dietary micronutrient and small molecule with critical roles in vision, immune system support, growth, cell differentiation, epithelial tissue maintenance, reproduction, and antioxidant protection[1][3][5][7]. Vitamin A can be consumed as preformed vitamin A (from animal foods) or as provitamin A carotenoids (from colorful plant foods), which are then metabolically converted to active retinoid forms in the body[6][7]. Deficiency leads to a range of disorders, while excess intake can have serious toxic effects. While retinoic acid (a metabolite) binds nuclear receptors (RAR, RXR) that regulate gene expression, "Vitamin A" as a term does not identify a single therapeutic target or protein[5].

Other names

RetinolRetinoic acidRetinalRetinolumVitamin A1all-trans-retinolall-trans-retinyl alcoholall-trans-vitamin A alcoholPreformed vitamin ARetinyl ester

As vitamin A (retinol): functions as a cofactor for opsin proteins for vision; metabolized to retinoic acid which binds nuclear receptors (RAR/RXR) to regulate gene transcription As retinoids (drugs): modulation of gene expression via nuclear retinoic acid receptors, leading to effects on cell differentiation and proliferation (anti-cancer, anti-acne, etc.)