Vitamin

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.

A "vitamin" is also a pill that contains vitamins, eaten regularly to keep one healthy.

Fruits and vegetables are a source of vitamins

The term was coined in 1912 by biochemist Casimir Funk, who isolated a complex of micronutrients and proposed the complex be named vitamine.^[1] By convention the word vitamin does not include other essential nutrients, such as certain minerals, essential fatty acids and essential amino acids.^[2]

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.^[3] 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 name[4][5]	Chemical name[4][5]	Reason for name change[4]
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 L1[6]	Anthranilic acid	No longer classified as a vitamin
Vitamin L2[6]	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 name	Active agent ('Vitamer') (list not complete)	Solubility	United States Recommended daily intake (male, age 19–70)[7]	Deficiency disease	Upper Intake Level (UL/day)[7]	Overdose disease	Food sources
Vitamin A	Retinol, retinal, and four carotenoids including beta carotene	Fat	900 µg	Night blindness, hyperkeratosis, and keratomalacia[8]	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[9]	Drowsiness or muscle relaxation with large doses.[10]	Pork, oatmeal, brown rice, vegetables, potatoes, liver, eggs
Vitamin B2	Riboflavin	Water	1.3 mg	Ariboflavinosis, glossitis, angular stomatitis	N/D		Dairy 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)[11] and other problems	Meat, fish, eggs, many vegetables, mushrooms, tree nuts
Vitamin B5	Pantothenic acid	Water	5.0 mg[12]	Paresthesia	N/D	Diarrhea; possibly nausea and heartburn.[13]	Meat, broccoli, avocados
Vitamin B6	Pyridoxine, pyridoxamine, pyridoxal	Water	1.3–1.7 mg	Anemia[14] 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/D		Raw 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 anemia[15]	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 megadosage	Many fruits and vegetables, liver
Vitamin D	Cholecalciferol (D3), Ergocalciferol (D2)	Fat	10 µg[16]	Rickets and osteomalacia	50 µg	Hypervitaminosis D	Fish, 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 infants[17]	1,000 mg	Increased congestive heart failure seen in one large randomized study.[18]	Many fruits and vegetables, nuts and seeds
Vitamin K	Phylloquinone, menaquinones	Fat	120 µg	Bleeding diathesis	N/D	Increases coagulation in patients taking warfarin.[19]	Leafy green vegetables such as spinach, egg yolks, liver

Related pages

• Dietary mineral
• Essential fatty acid
• Essential amino acid