Vitamin

A "vitamin" is also a pill that contains vitamins, eaten regularly to keep one healthy.
A vitamin is a chemical compound that is needed in small amounts for the human body to work correctly. They include Vitamin A, many B vitamins (like B1, B2, B3, B6, and B12), Vitamin C, Vitamin D, Vitamin E, and Vitamin K. For example, citrus fruits such as oranges and lemons contain vitamin C. 

The term was coined in 1912 by biochemist Casimir Funk, who isolated a complex of micronutrients and proposed the complex be named vitamine. By convention the word vitamin does not include other essential nutrients, such as certain minerals, essential fatty acids and essential amino acids. 

Thirteen vitamins are recognized at present. Vitamins are classified by their biological and chemical activity, and not their structure. Each vitamin name (the word vitamin followed by a letter) refers to a number of vitamer compounds which all show the same biological activity. For example, vitamin A refers to several different chemicals.  Vitamers convert to the active form of the vitamin in the body. They are sometimes inter-convertible to one another as well.

The body does not make these chemicals. They come from other places, usually food. A short term lack of a certain vitamin is usually not a problem, because the body can store vitamins for a short time. Not having a certain vitamin for a longer period of time can lead to different diseases, depending on the vitamin. Probably the best-known of these diseases is scurvy, which results from not having enough Vitamin C. Beriberi and rickets are others. 

Today, many drug companies make inexpensive pills that contain various vitamins. They help people avoid those diseases.

Vitamins can be either fat-soluble or water-soluble.  Fat-soluble vitamins (A, D, E and K) can be stored in the body, and are used when needed.  Water-soluble ones only stay in the body a short time.

 Name changes 
Currently there are no vitamins F to J.  These existed at some time.  Today they are no longer seen as vitamins.  Some of them were also false leads, and turned out to be something else.  Others were renamed as B vitamins.  Today, the B vitamins are a whole complex, and not just one vitamin. 

The German-speaking scientists who isolated and described vitamin K (in addition to naming it as such) did so because the vitamin is intimately involved in the 'Koagulation' (clotting) of blood following wounding. At the time, most (but not all) of the letters from F through I were already designated, so the use of the letter K was considered quite reasonable.
The following table lists chemicals that had previously been classified as vitamins, as well as the earlier names of vitamins that later became part of the B-complex. 
 Previous nameEvery Vitamin Page  All Vitamins and Pseudo-Vitamins. Compiled by David Bennett. Chemical name Reason for name change Vitamin B4 Adenine  No longer classified as a vitamin Vitamin B8 Adenylic acid  No longer classified as a vitamin Vitamin F Essential fatty acids Needed in large quantities (does not fit the definition of a vitamin). Vitamin G Riboflavin Reclassified as Vitamin B2 Vitamin H Biotin Reclassified as Vitamin B7 Vitamin J Catechol, Flavin No longer classified as a vitamin Vitamin L1Michael W. Davidson (2004) Anthranilic Acid (Vitamin L) Florida State University. Accessed 20-02-07 Anthranilic acid No longer classified as a vitamin Vitamin L2 Adenylthiomethylpentose No longer classified as a vitamin Vitamin M Folic acid   Reclassified as Vitamin B9 Vitamin O  Carnitine No longer classified as a vitamin Vitamin P Flavonoids  No longer classified as a vitamin Vitamin PP Niacin Reclassified as Vitamin B3  Vitamin U  S-Methylmethionine No longer classified as a vitamin

 List of vitamins 
Vitamin generic descriptor nameActive agent ('Vitamer') (list not complete)SolubilityUnited States Recommended daily intake(male, age 19–70)Dietary Reference Intakes: Vitamins . The National Academies, 2001. Deficiency diseaseUpper Intake Level (UL/day) Overdose disease Food sources Vitamin A Retinol, retinal, andfour carotenoids including beta carotene Fat 900 µg Night blindness, hyperkeratosis, and keratomalacia 3,000 µg Hypervitaminosis A Liver, orange, ripe yellow fruits, leafy vegetables, carrots, pumpkin, squash, spinach, fish, soy milk, milk Vitamin B1 Thiamine Water 1.2 mg Beriberi, Wernicke-Korsakoff syndrome N/D Drowsiness or muscle relaxation with large doses.Pork, oatmeal, brown rice, vegetables, potatoes, liver, eggs Vitamin B2 Riboflavin Water 1.3 mg Ariboflavinosis, glossitis, angular stomatitis N/DDairy products, bananas, popcorn, green beans, asparagus Vitamin B3 Niacin, niacinamide, Nicotinamide riboside Water 16.0 mg Pellagra 35.0 mg Liver damage (doses > 2g/day) and other problemsMeat, fish, eggs, many vegetables, mushrooms, tree nuts Vitamin B5 Pantothenic acid Water 5.0 mgPlain type indicates Adequate Intakes (A/I). "The AI is believed to cover the needs of all individuals, but a lack of data prevent being able to specify with confidence the percentage of individuals covered by this intake" (see Dietary Reference Intakes: Vitamins . The National Academies, 2001). Paresthesia N/D Diarrhea; possibly nausea and heartburn.Meat, broccoli, avocados Vitamin B6 Pyridoxine, pyridoxamine, pyridoxal Water 1.3–1.7 mg AnemiaVitamin and Mineral Supplement Fact Sheets Vitamin B6 . Dietary-supplements.info.nih.gov (15 September 2011). Retrieved on 2013-08-03. peripheral neuropathy 100 mg Impairment of proprioception, nerve damage (doses > 100 mg/day)Meat, vegetables, tree nuts, bananas Vitamin B7 Biotin Water 30.0 µg Dermatitis, enteritis N/DRaw egg yolk, liver, peanuts, leafy green vegetables Vitamin B9 Folates Water 400 µg Megaloblastic anemia and deficiency during pregnancy is associated with birth defects, such as neural tube defects 1,000 µg May mask symptoms of vitamin B12 deficiency; other effects.Leafy vegetables, pasta, bread, cereal, liver Vitamin B12 Cyanocobalamin, hydroxocobalamin, methylcobalamin, adenosylcobalamin Water 2.4 µg Pernicious anemiaVitamin and Mineral Supplement Fact Sheets Vitamin B12 . Dietary-supplements.info.nih.gov (24 June 2011). Retrieved on 2013-08-03. N/D Acne-like rash [causality is not conclusively established].Meat, poultry, fish, eggs, milk Vitamin C Ascorbic acid Water 90.0 mg Scurvy 2,000 mg Vitamin C megadosageMany fruits and vegetables, liverVitamin D Cholecalciferol (D3), Ergocalciferol (D2) Fat 10 µgValue represents suggested intake without adequate sunlight exposure (see Dietary Reference Intakes: Vitamins . The National Academies, 2001). Rickets and osteomalacia 50 µg Hypervitaminosis DFish, eggs, liver, mushrooms Vitamin E Tocopherols, tocotrienols Fat 15.0 mg Deficiency is very rare; sterility in males and miscarriage in females, mild hemolytic anemia in newborn infantsThe Merck Manual: Nutritional Disorders: Vitamin Introduction Please select specific vitamins from the list at the top of the page. 1,000 mg Increased congestive heart failure seen in one large randomized study.Many fruits and vegetables, nuts and seeds Vitamin K Phylloquinone, menaquinones Fat 120 µg Bleeding diathesis N/D Increases coagulation in patients taking warfarin. Leafy green vegetables such as spinach, egg yolks, liver

Related pages
 Dietary mineral
 Essential fatty acid
 Essential amino acid

 References