Vitamin A is an essential micronutrient for humans, meaning that it cannot be biosynthesized in the body and thus must be obtained from dietary sources.
Vitamin A is a fat-soluble vitamin and also comprises of a group of unsaturated nutritional organic compounds. These compounds include preformed vitamin A that exist in the form of retinol (alcohol), retinal (aldehyde), retinoic acid (irreversibly oxidized form of retinol) and several pro-vitamin A carotenoids (mainly β–caro-tene). The preformed vitamin A can only be obtained from the diet in food of animal origin and is the most abundant form of vitamin A in the human body.
Vitamin A is mainly found in human tissues in the form of retinyl esters, which explains why the vitamin is commercially produced and administered as esters of retinyl acetate or palmitate.
Retinoic acid (RA) is the active form of the retinol isoform of vitamin A, which functions as a hormone-like growth factor for epithelial cells and many other cell types of different tissues in the human body. In the absence of dietary fat-soluble vitamin A, epithelial cells of the renal system can undergo typical changes that predispose to the formation of concretions (urinary calculi) in the urinary tract.
A sufficient vitamin A (retinol) intake is essential for:
• the process of vision (especially night vision)
• growth and development, it is involved in the genetic regulation of cell and tissue formation, programming, and communication needed for reproduction and for the proper development of the embryo in the womb
• immune function it helps to protect against infections by ensuring the effectiveness of mechanical barriers (e.g., skin, mucosa), and increasing the production and efficacy of protective cells (e.g., lymphocytes)
• male and female reproductive organs.
Fat soluble vitamin: Vitamin A
