Retinol

Retinol, also known as Vitamin A1, is a vitamin found in food and used as a dietary supplement. As a supplement it is used to treat and prevent vitamin A deficiency, especially that which results in xerophthalmia. In areas where deficiency is common, a single large dose is recommended to those at high risk a couple of times a year. It is also used to reduce the risk of complications in those who have measles. It is used by mouth or injection into a muscle. Retinol, also known as Vitamin A1, is a vitamin found in food and used as a dietary supplement. As a supplement it is used to treat and prevent vitamin A deficiency, especially that which results in xerophthalmia. In areas where deficiency is common, a single large dose is recommended to those at high risk a couple of times a year. It is also used to reduce the risk of complications in those who have measles. It is used by mouth or injection into a muscle. Retinol at normal doses is well tolerated. High doses may result in an enlarged liver, dry skin, or hypervitaminosis A. High doses during pregnancy may result in harm to the baby. Retinol is in the vitamin A family. It or other forms of vitamin A are needed for eyesight, maintenance of the skin, and human development. It is converted in the body to retinal and retinoic acid through which it acts. Dietary sources include fish, dairy products, and meat. Retinol was discovered in 1909, isolated in 1931, and first made in 1947. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. Retinol is available as a generic medication and over the counter. The wholesale cost in the developing world is about US$0.02–0.30 per 50,000 units. In the United States it is not very expensive. Retinol is used to treat vitamin A deficiency. Three approaches may be used when populations have low vitamin A levels: The Tolerable Upper Intake Level (UL) for vitamin A, for a 25-year-old male, is 3,000 micrograms/day, or about 10,000 IU. If nursing, vitamin A intake should be 1,200 to 1,300 retinol activity units (RAE). Too much vitamin A in retinoid form can be harmful or fatal, resulting in what is known as hypervitaminosis A. The body converts the dimerized form, carotene, into vitamin A as it is needed, therefore high levels of carotene are not toxic compared to the ester (animal) forms. The livers of certain animals, especially those adapted to polar environments such as polar bears and seals, often contain amounts of vitamin A that would be toxic to humans. Thus, vitamin A toxicity is typically reported in Arctic explorers and people taking large doses of synthetic vitamin A. The first documented death possibly caused by vitamin A poisoning was Xavier Mertz, a Swiss scientist who died in January 1913 on an Antarctic expedition that had lost its food supplies and fell to eating its sled dogs. Mertz may have consumed lethal amounts of vitamin A by eating the dogs' livers. Vitamin A acute toxicity occurs when an individual ingests vitamin A in large amounts more than the daily recommended value in the threshold of 25,000 IU/kg or more. Often, the individual consumes about 3–4 times the RDA's specification. Toxicity of vitamin A is believed to be associated with the intervention methods used to upgrade vitamin A levels in the body such as food modification, fortification and supplementation, all of which are employed to combat vitamin A deficiency Toxicity is classified into two categories: acute and chronic toxicities. The former occurs few hours or days after ingestion of large amounts of vitamin A accidentally or via inappropriate therapy. The later toxicity (Chronic) takes place when about 4,000 IU/kg or more of vitamin A is consumed for a prolonged period of time. Symptoms associated with both toxicities include nausea, blurred vision, fatigue, weight-loss, menstrual abnormalities etc. 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. An excessive uptake of carotenoids can, however, cause carotenosis.