The structure of retinol, the most common dietary form of vitamin A

Vitamin A is an essential human nutrient. It exists not as a single compound, but in several forms. In foods of animal origin, the major form of vitamin A is an alcohol (retinol), but can also exist as an aldehyde (retinal), or as an acid (retinoic acid). Precursors to the vitamin (a provitamin) are present in foods of plant origin as some of the members of the carotenoid family of compounds.^[1] Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... This article does not cite any references or sources. ... Retinol, the animal form of vitamin A, is a yellow fat-soluble, antioxidant vitamin important in vision and bone growth. ... An aldehyde. ... Retinal, technically called retinene1 or retinaldehyde, is a light-sensitive retinene molecule found in the photoreceptor cells of the retina. ... Retinoic acid, or Retin-A or vitamin A acid, is a carotenoid organic compound that is a component of visual pigments. ... A provitamin is a substance that can be converted into a vitamin by animal tissues. ... The orange ring surrounding Grand Prismatic Spring is due to carotenoid molecules, produced by huge mats of algae and bacteria. ...

All forms of Vitamin A have a Beta-ionone ring to which an isoprenoid chain is attached. This structure is essential for vitamin activity.^[1] Ionone or 4-(2,6,6-trimethyl-1-cyclohexen-1-yl)-3-Buten-2-one or cyclocitrylideneacetone or irisone C13H20O is a chemical substance and part of the terpene family. ... Isoprene is a common synonym for the chemical compound 2-methyl-1,3-butadiene. ...

• retinol, the animal form of Vitamin A, is a yellow, fat-soluble, vitamin with importance in vision and bone growth.

• other retinoids, a class of chemical compounds that are related chemically to Vitamin A, are used in medicine.^[2]

Retinol, the animal form of vitamin A, is a yellow fat-soluble, antioxidant vitamin important in vision and bone growth. ... Retinol (Vitamin A) For the record label, see Vitamin Records A vitamin is an organic compound required in tiny amounts for essential metabolic reactions in a living organism. ... The Retinoids are a class of chemical compounds that are related chemically to vitamin A. Retinoids are used in medicine, primarily due to the way they regulate epithelial cell growth. ...

Discovery of Vitamin A

The discovery of Vitamin A stemmed from research dating back to 1906, indicating that factors other than carbohydrates, proteins, and fats were necessary to keep cattle healthy.^[3] By 1917 one of these substances was independently discovered by Elmer McCollum at the University of Wisconsin-Madison, and Lafayette Mendel and Thomas Osborne at Yale University. Since "water-soluble factor B" (Vitamin B) had recently been discovered, the researchers chose the name "fat-soluble factor A".^[3] 1906 (MCMVI) was a common year starting on Monday (see link for calendar). ... Lactose is a disaccharide found in milk. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... For other uses, see FAT. Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. ... For general information about the genus, including other species of cattle, see Bos. ... 1917 (MCMXVII) was a common year starting on Monday of the Gregorian calendar (see link for calendar) or a common year starting on Tuesday of the 13-day slower Julian calendar (see: 1917 Julian calendar). ... Associated with the discovery of Vitamin A, Elmer McCollum was a biochemist at the University of Wisconsin, who in 1913, along with colleague Marguerite Davis identified a fat-soluble nutrient in butterfat and cod liver oil[1]. McCollum and Davis research validated that of Thomas Osborne and Lafayette Mendel, then... University of Wisconsin redirects here. ... Lafayette Benedict Mendel (February 5, 1872 – December 9, 1935) was an American biochemist known for his work in nutrition including the study of Vitamin A, Vitamin B, lysine and tryptophan. ... Yale redirects here. ... Vitamin B is a complex of several vitamins. ...

Equivalencies of retinoids and carotenoids (IU)

Vitamin A intake is often expressed in international units (IU) or as retinol equivalents (RE), with 1 IU = 0.3 micrograms retinol. Because the production of retinol from provitamins by the human body is regulated by the amount of retinol available to the body, the conversions apply strictly only for Vitamin A deficient humans. The absorption of provitamins also depends greatly on the amount of lipids ingested with the provitamin; lipids increase the uptake of the provitamin.^[4] In pharmacology, the International unit (IU, alternatively abbreviated UI, from French unité internationale) is a unit of measurement for the amount of a substance, based on measured biological activity (or effect). ...

Conversion of carotenoids into retinol relies on adequate intake of vitamin C, vitamin E, zinc and protein.^{[citation needed]} This article is about the nutrient. ... Tocopherol, or Vitamin E, is a fat-soluble vitamin in eight forms that is an important antioxidant. ... General Name, symbol, number zinc, Zn, 30 Chemical series transition metals Group, period, block 12, 4, d Appearance bluish pale gray Standard atomic weight 65. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...

Recommended daily intake

Vitamin A US Dietary Reference Intake: The Dietary Reference Intake is a system of nutrition recommendations from the Institute of Medicine of the USA National Academy (IOM). ...

• 900 micrograms (3000 IU) for men
• 700 for (2300 IU) women.
• Upper limit - 3,000 micrograms (10,000 IU).

(Note that the limit refers to retinoid forms of vitamin A. Carotene forms from dietary sources are not toxic.^[5]) The Retinoids are a class of chemical compounds that are related chemically to vitamin A. Retinoids are used in medicine, primarily due to the way they regulate epithelial cell growth. ... β-Carotene represented by a 3-dimensional stick diagram Carotene is responsible for the orange colour of the carrots and many other fruits and vegetables. ... Diet may mean: In nutrition: Diet (nutrition), the sum of the food consumed by an organism or group. ... Toxic redirects here, but this is also the name of a song by Britney Spears; see Toxic (song) Look up toxic and toxicity in Wiktionary, the free dictionary. ...

Sources

Vitamin A is found naturally in many foods. Each of the following contains at least 0.15 mg (which is equal to 150 micrograms -500 IU). See Recommended Daily Intake.) of Vitamin A or beta carotene per 1.75-7 oz. (50-200 g):

note: bracketed values are retinol equivalences and percentage of RDI per 100g. For the bird, see Liver bird. ... Binomial name Daucus carota A carrot (Daucus Carota) is a root vegetable, typically orange or white in color with a woody texture. ... Broccoli is a plant of the Cabbage family, Brassicaceae (formerly Cruciferae). ... Binomial name Ipomoea batatas Linnaeus, The sweet potato (Ipomoea batatas) is a crop plant whose large, starchy, sweet-tasting tuberous roots are an important root vegetable. ... Kale or Borecole is a form of cabbage (Brassica oleracea Acephala Group), green in color, in which the central leaves do not form a head. ... For other uses, see Butter (disambiguation). ... Binomial name Spinacia oleracea L. Percentages are relative to US recommendations for adults. ... Fresh Swiss chard Fresh water spinach Creamed spinach Steamed kale Leaf vegetables, also called greens or leafy greens, are plant leaves eaten as a vegetable, sometimes accompanied by tender petioles and shoots. ... For other uses, see Pumpkin (disambiguation). ... Collards, also called collard greens or borekale (Brassica oleracea Acephala Group), are various loose-leafed cultivars of the cabbage plant. ... Trinomial name Cucumis melo cantalupensis Cucumis melo reticulatus Naudin. ... An egg is a body consisting of an ovum surrounded by layers of membranes and an outer casing of some type, which acts to nourish and protect a developing embryo. ... Binomial name Prunus armeniaca The scientific name for the apricot is Prunus armeniaca L., which puts it in the same subgenus as the plum (Prunophora). ... Binomial name L. This article is about the fruit. ... Species About 35 species, including: Mangifera altissima Mangifera applanata Mangifera caesia Mangifera camptosperma Mangifera casturi Mangifera decandra Mangifera foetida Mangifera gedebe Mangifera griffithii Mangifera indica Mangifera kemanga Mangifera laurina Mangifera longipes Mangifera macrocarpa Mangifera mekongensis Mangifera odorata Mangifera pajang Mangifera pentandra Mangifera persiciformis Mangifera quadrifida Mangifera siamensis Mangifera similis Mangifera... Broccoli is a plant of the Cabbage family, Brassicaceae (formerly Cruciferae). ... Binomial name Pisum sativum A pea (Pisum sativum) is the small, edible round green seed which grows in a pod on a leguminous vine, hence why it is called a legume. ... A beet (called beetroot in the United Kingdom and its former colonies, as well as table beet, garden beet, blood turnip or red beet) is a plant of the genus Beta of which both the leaves and root are edible. ... Winter squash is a warm-seasoned vegetable. ...

Deficiency

Night blindness, corneal drying (xerosis), triangular grey spots on eye (Bitot's spots), corneal degeneration and blindness (xerophthalmia)^[7], impaired immunity, hypokeratosis (white lumps at hair follicles), keratosis pilaris, and softening of the cornea (keratomalacia). Retinol, the animal form of vitamin A, is a yellow fat-soluble, antioxidant vitamin important in vision and bone growth. ... Xerosis is the medical term for dry skin. ... Bitots spots are located superficially in the conjunctiva, which are oval, triangular or irregular in shape. ... Xerophthalmia (Greek for dry eyes) is a medical condition in which the eye doesnt produce tears. ... Keratosis pilaris (KP) is a very common genetic follicular condition that is manifested by the appearance of rough bumps on the skin and hence colloquially referred to as chicken skin. It most often appears on the back and outer sides of the upper arms (though the lower arms can also... Keratomalacia is a eye disorder that leads to a dry cornea. ...

Overdose

Main article: Hypervitaminosis A

As vitamin A is fat-soluble, disposing of any excesses taken in through diet is much harder than with water-soluble vitamins B and C. As such, vitamin A toxicity can result. This can lead to nausea, jaundice, irritability, anorexia (not to be confused with anorexia nervosa, the eating disorder), vomiting, blurry vision, headaches, muscle and abdominal pain and weakness, drowsiness and altered mentality. The effects of excessive vitamin A intake include: birth defects liver abnormalities, reduced bone mineral density that may result in osteoporosis coarse bone growths hair loss excessive skin dryness/peeling Signs of acute toxicity include nausea and vomiting, headache, dizziness, blurred vision, and loss of muscular coordination. ... Anorexia (deriving from the Greek α(ν)- (a(n)-, a prefix that denotes absence) + όρεξη (orexe) = appetite) is the decreased sensation of appetite. ... For other uses, see Anorexia. ...

Acute toxicity generally occurs at doses of 25,000 IU/kg, with chronic toxicity occurring at 4,000 IU/kg daily for 6-15 months.^[8] However, liver toxicities can occur at levels as low as 15,000IU per day to 1.4 million IU per day, with an average daily toxic dose of 120,000IU per day. In people with renal failure 4000IU can cause substantial damage. Additionally excessive alcohol intake can increase toxicity.^[9]

In chronic cases, hair loss, drying of the mucous membranes, fever, insomnia, fatigue, weight loss, bone fractures, anaemia, and diarrhoea can all be evident on top of the symptoms associated with less serious toxicity.^[10]

These toxicities only occur with preformed (retinoid) vitamin A (such as from liver), the caretonoid forms (such as beta carotene as found in carrots) give no such symptoms.

See also

• Beta carotene
• Hypervitaminosis A

Beta-carotene is a form of carotene with β-rings at both ends. ... The effects of excessive vitamin A intake include: birth defects liver abnormalities, reduced bone mineral density that may result in osteoporosis coarse bone growths hair loss excessive skin dryness/peeling Signs of acute toxicity include nausea and vomiting, headache, dizziness, blurred vision, and loss of muscular coordination. ...

External links

• MeSH Vitamin+A

Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. ...

References

1. ^ ^{a b} Carolyn Berdanier. 1997. Advanced Nutrition Micronutrients. pp 22-39
2. ^ American Cancer Society: Retinoid Therapy
3. ^ ^{a b} Wolf, George (2001-04-19). "Discovery of Vitamin A". Encyclopedia of Life Sciences. doi:10.1038/npg.els.0003419. Retrieved on 2007-07-21. 
4. ^ NW Solomons, M Orozco. Alleviation of Vitamin A dfgdhgjghkhfljh;krsfdatdtkhgl;kjml./.eficiency with palm fruit and its products. Asia Pac J Clin Nutr, 2003
5. ^ Sources of vitamin A. Retrieved on 2007-08-27.
6. ^ [1]
7. ^ Roncone DP (2006). "Xerophthalmia secondary to alcohol-induced malnutrition". Optometry (St. Louis, Mo.) 77 (3): 124-33. doi:10.1016/j.optm.2006.01.005. PMID 16513513. Retrieved on 2007-08-18. 
8. ^ [2]
9. ^ [3]
10. ^ http://www.emedicine.com/med/topic2382.htm