What Is Vitamin A?
The term “Vitamin A” refers to a group of related compounds, but most commonly to a fat-soluble vitamin called retinol (Vitamin A1), which is an alcohol.
In a broader sense, the term can also include the aldehyde form retinal, the carboxylic acid retinoic acid, and their 3-dehydro forms (called vitamin A2), as well as related substances and derivatives.
Retinol, the principal substance, has the chemical formula C20H30O, a molecular weight of 286.4516, and CAS number 68-26-8. Its melting point is 62-64°C and boiling point is 137-138°C.
It is insoluble in water, susceptible to oxidation, and easily decomposed by air, oxygen, moisture, heat, and light. It is an essential nutrient that promotes skin cell differentiation and is known to play a role in maintaining healthy skin and mucous membranes.
Uses of Vitamin A
Vitamin A is a generic term that refers to retinol, retinal, and retinoic acid, but most vitamin A in human blood is retinol. Retinol is an essential nutrient and has uses as a dietary supplement and in pharmaceuticals because it promotes skin cell differentiation.
Among vitamin A, retinoic acid has been reported to have many skin-related effects and is approved as a treatment for acne in the United States. In Japan, the indication labeling of retinol as a wrinkle-improving agent in cosmetics has been approved as a quasi-drug.
Characteristics of Vitamin A
Retinol (alcohol form), called vitamin A1, is oxidized to retinal (aldehyde form) and retinoic acid (carboxylic acid), in that order. In fact, these substances are the main body of the active action. These are broadly classified as Vitamin A, and their analogues are called retinoids. Retinal is involved in vision, and retinoic acid is involved in the regulation of gene expression.
There are other substances that, when ingested, produce the physiological effects of vitamin A in the body. These include retinyl fatty acid esters and carotenoids classified as vitamin A.
There are approximately 50 types of provitamin A, including β-carotene. The carotenoids are unique in that they do not cause overdose; β-carotene is broken down in the body in the absorptive epithelial cells of the small intestine or in the liver and kidneys to form vitamin A.
Generally, retinyl fatty acid esters are found in animal products, while vitamin A carotenoids are mainly found in plant products.
Types of Vitamin A
Vitamin A is widely available as a dietary supplement and as a pharmaceutical agent because it is an essential nutrient. Because it is a fat-soluble vitamin, capsules are often used as the dosage form.
However, it is important to note that excessive intake of retinol can cause dizziness, nausea, headache, coma, and may be fatal. In addition, excessive intake by pregnant women may lead to birth defects in the fetus.
Vitamin A is also used in experimental research. In addition to being sold as pure retinol, it may also be available as retinol acetate or as retinol palmitate standard solution for HPLC.
Other Information on Vitamin A
Bioactivity of Vitamin A
As an essential nutrient vitamin A, is essential for the proper functioning of the human body. For example, retinol is an essential nutrient that promotes skin cell differentiation and is used to protect retinal cells. When retinol is deficient, rhodopsin in photoreceptor cells ceases to function and night blindness develops.
Rhodopsin is a photopigment that is important in triggering light-induced excitation (optokinesis) in photoreceptor cells. It is also necessary for the immune system, the regulation of genetic information in DNA reproductive functions, and helps the heart, lungs, kidneys, and other organs to function properly.