Not to be confused with Retinal. Retinol, also known as Vitamin A1, is a vitamin found in food and used as a methods of research of organs of hematopoiesis in children supplement.
Retinol at normal doses is well tolerated. High doses may result in an enlarged liver, dry skin, or hypervitaminosis A. Retinol was discovered in 1909, isolated in 1931, and first made in 1947. Retinol is used to treat vitamin A deficiency. Too much vitamin A in retinoid form can be harmful or fatal, resulting in what is known as hypervitaminosis A.
Excess vitamin A has also been suspected to be a contributor to osteoporosis. This seems to happen at much lower doses than those required to induce acute intoxication. Only preformed vitamin A can cause these problems, because the conversion of carotenoids into vitamin A is downregulated when physiological requirements are met. Dietary supplementation with β-carotene was interestingly associated with an increase in lung cancer when it was studied in a lung cancer prevention trial in male smokers.
In non-smokers, the opposite effect has been noted. Excess preformed vitamin A during early pregnancy has also been associated with a significant increase in birth defects. These defects may be severe, even life-threatening. Even twice the daily recommended amount can cause severe birth defects. A deficiency is common and maternal mortality is high, dosing expectant mothers can greatly reduce the maternal mortality rate. Retinoic acid via the retinoic acid receptor influences the process of cell differentiation, hence, the growth and development of embryos.
Cells in the embryo respond to retinoic acid differently depending on the amount present. For example, in vertebrates the hindbrain transiently forms eight rhombomers and each rhombomere has a specific pattern of genes being expressed. Retinoic acid is an influential factor used in differentiation of stem cells to more committed fates, echoing retinoic acid’s importance in natural embryonic developmental pathways. It is thought to initiate differentiation into a number of different cell lineages by unsequestering certain sequences in the genome.
Vitamin A is converted by the protein RPE65 within the retinal pigment epithelium into 11-cis-retinal. This molecule is then transported into the photoreceptor cells of the retina, where it acts as a light-activated molecular switch within opsin proteins that activates a complex cascade called the visual cycle. This cycle begins with 11-cis retinal absorbing light and isomerizing into all-trans retinal. Vitamin A is essential for the correct functioning of epithelial cells. Glycoprotein synthesis requires adequate vitamin A status. In severe vitamin A deficiency, lack of glycoproteins may lead to corneal ulcers or liquefaction. Vitamin A affects the production of human growth hormone.
IU refers to biological activity and therefore is unique to each individual compound, however 1 IU of retinol is equivalent to approximately 0. Vitamin A also acts in the body as an antioxidant, a protective chemical that may reduce the risk of certain cancers. There are two sources of dietary vitamin A. Active forms, which are immediately available to the body are obtained from animal products. These are known as retinoids and include retinaldehyde and retinol.