Vitamin A (vitaminA), also known as retinol (its aldehyde derivative retinaldehyde) is an unsaturated monohydric alcohol with an ester ring, including vitamin A 1, A2 two. (Vitamins A1 and A2 are structurally similar.) Retinol can be synthesized from plant sources of β - carotene, catalyzed by β - carotene-15, 15′ - dioxygenase (dioxygenase) in vivo, β - carotene can be converted to two molecules of retinaldehyde (ratinal, retinaldehyde in the retinaldehyde reductase under the action of the retinoid reduction enzyme is reduced to retinol. Therefore, β - carotene is also known as vitamin A original. It is the United States of America in 1913, the chemist Tavis extracted from the cod liver. It is a yellow powder, insoluble in water, soluble in fat, oil and other organic solvents. It is chemically stable, but is easily destroyed by ultraviolet light and should be stored in brown bottles. Vitamin A is a component of the retinoschisin that makes up the retinal pigment of visual cells that perceive low light Retinoschisin is composed of retinoids and ``11 -cis-retinaldehyde, which is associated with dark vision. Vitamin A is found only in animal foods; A1 is found in the livers of mammals and saltwater fish, while A2 is found in the livers of freshwater fish. Vitamin A has not been found in plant tissues.Vitamin A deficiency in the human body affects dark adaptation, such as stunted growth in children, dry skin, dry eye disease, and night blindness. The minimum daily requirement of vitamin A for normal adults is about 3500 international units (0.3 micrograms of vitamin A is equivalent to 1 international unit), and for children it is about 2000 to 2500 international units. CAS No.: 11103-57-4 Functions of Vitamin A: Maintain normal visual response. Maintain normal form and function of epithelial tissue. Maintain normal bone development. Maintain the function of skin cells, which can make the skin soft and tender, and have the effect of anti-wrinkle and wrinkle. Lack of vitamin A will make the function of epithelial cells decline, resulting in decreased skin elasticity, dryness, roughness, loss of luster. Physiological functions of vitamin A: Vitamin A is an essential nutrient for the complex organism, which affects almost all tissue cells of the organism in different ways. Despite being one of the first vitamins to be discovered, its physiological functions have not yet been fully uncovered. As far as current knowledge is concerned, the most important physiological functions of vitamin A (including carotenoids) include: (1) maintenance of vision (2) promotion of growth (3) enhancement of fertility (4) scavenging of free radicals, etc. Vitamin A absorption and metabolism: Vitamin A is emulsified in the small intestine along with bile acid lipolysis products, and absorbed by the intestinal mucosa. Vitamin A human body storage increases with age, to old age is significantly lower than young people, different sex storage also different. The average half-life of vitamin A in the body is 128-154 days, and the daily rate of loss (catabolism) in the liver is about 0.5% in the absence of vitamin A intake. Vitamin A-rich foods are of two types: one is vitamin A proto, i.e., various carotenoids, which are found in plant foods, such as leafy greens, yellow vegetables, and fruits, with richer contents of spinach, alfalfa, pea shoots, sweet potatoes with red hearts, carrots, green peppers, and pumpkins, etc. The other is vitamin A from animal foods, which is vitamin A capable of being directly utilized by the human body, and which is mainly found in animal liver, milk and milk products (unskimmed milk) and poultry eggs. Vitamin A Side Effects Adults who consume more than 50,000 IU per day for several months can cause toxicity. Young children can be poisoned if they consume more than 18,500 IU in a day. Main manifestations: Increased osteoclast activity, resulting in bone decalcification, increased bone brittleness, impaired growth, thickening of long bones, and bone and joint pain; dry, itchy, scaly skin, rashes, peeling, hair loss, brittle fingernails; agitation, fatigue, headache, nausea, vomiting, muscle weakness, and fidgeting. Decreased appetite, abdominal pain, diarrhea, enlarged liver and spleen, jaundice; decreased hemoglobin and potassium in the blood, prolonged clotting time, easy bleeding.