Vitamins
A vitamin is an organic compound and a vital nutrient that an organism requires in limited amounts. An organic chemical compound (or related set of compounds) is called a vitamin when the organism cannot synthesize the compound in sufficient quantities, and it must be obtained through the diet; thus, the term vitamin is conditional upon the circumstances and the particular organism. For example, ascorbic acid (one form of vitamin C) is a vitamin for humans, but not for most other animal organisms. Supplementation is important for the treatment of certain health problems,[1] but there is little evidence of nutritional benefit when used by otherwise healthy people.[2]
By convention the term vitamin does not include other essential nutrients, such as dietary minerals, essential fatty acids, essential amino acids (which are needed in greater amounts than vitamins) or the many other nutrients that promote health, and are required less often to maintain the health of the organism.[3] Thirteen vitamins are universally recognized at present. Vitamins are classified by their biological and chemical activity, not their structure. Thus, each vitamin refers to a number of vitamer compounds that all show the biological activity associated with a particular vitamin. Such a set of chemicals is grouped under an alphabetized vitamin "generic descriptor" title, such as "vitamin A", which includes the compounds retinal, retinol, and four known carotenoids. Vitamers by definition are convertible to the active form of the vitamin in the body, and are sometimes inter-convertible to one another, as well.
Vitamins have diverse biochemical functions. Some, such as vitamin D, have hormone-like functions as regulators of mineral metabolism, or regulators of cell and tissue growth and differentiation (such as some forms of vitamin A). Others function as antioxidants (e.g., vitamin E and sometimes vitamin C).[4] The largest number of vitamins, the B complex vitamins, function as enzyme cofactors (coenzymes) or the precursors for them; coenzymes help enzymes in their work as catalysts in metabolism. In this role, vitamins may be tightly bound to enzymes as part of prosthetic groups: For example, biotin is part of enzymes involved in making fatty acids. They may also be less tightly bound to enzyme catalysts as coenzymes, detachable molecules that function to carry chemical groups or electrons between molecules. For example, folic acid may carry methyl, formyl, and methylene groups in the cell. Although these roles in assisting enzyme-substrate reactions are vitamins' best-known function, the other vitamin functions are equally important.[5]
Until the mid-1930s, when the first commercial yeast-extract vitamin B complex and semi-synthetic vitamin C supplement tablets were sold, vitamins were obtained solely through food intake, and changes in diet (which, for example, could occur during a particular growing season) usually greatly altered the types and amounts of vitamins ingested. However, vitamins have been produced as commodity chemicals and made widely available as inexpensive semisynthetic and synthetic-source multivitamin dietary and food supplements and additives, since the middle of the 20th century. Study of structural activity, function and their role in maintaining health is called vitaminology.[6]
- 1List of vitamins
- 2Health effects
- 3Pharmacology
- 4History
- 5Society and culture
- 6Anti-vitamins
- 7See also
- 8References
- 9External links
List of vitamins[edit]
Each vitamin is typically used in multiple reactions, and therefore most have multiple functions.[7]
Vitamin generic descriptor name | Vitamer chemical name(s) (list not complete) | Solubility | United States Recommended dietary allowances (male, age 19–70)[8] | Deficiency disease | Upper Intake Level (UL/day)[8] | Overdose disease | Food sources |
|---|---|---|---|---|---|---|---|
| Vitamin A |
four carotenoids including beta carotene | Fat | 900 µg | Night blindness, hyperkeratosis, and keratomalacia[9] | 3,000 µg | Hypervitaminosis A | Liver, orange, ripe yellow fruits, leafy vegetables, carrots, pumpkin, squash, spinach, fish, soya milk, milk |
| Vitamin B~1 | Thiamine | Water | 1.2 mg | Beriberi, Wernicke-Korsakoff syndrome | N/D[10] | Drowsiness or muscle relaxation with large doses.[11] | Pork, oatmeal, brown rice, vegetables, potatoes, liver, eggs |
| Vitamin B~2 | Riboflavin | Water | 1.3 mg | Ariboflavinosis, glossitis, angular stomatitis | N/D | Dairy products, bananas, popcorn, green beans, asparagus | |
| Vitamin B~3 | Niacin, niacinamide, Nicotinamide riboside | Water | 16.0 mg | Pellagra | 35.0 mg | Liver damage (doses > 2g/day)[12]and other problems | Meat, fish, eggs, many vegetables, mushrooms, tree nuts |
| Vitamin B~5 | Pantothenic acid | Water | 5.0 mg[13] | Paresthesia | N/D | Diarrhea; possibly nausea and heartburn.[14] | Meat, broccoli, avocados |
| Vitamin B~6 | Pyridoxine, pyridoxamine, pyridoxal | Water | 1.3–1.7 mg | Anemia[15] peripheral neuropathy | 100 mg | Impairment of proprioception, nerve damage (doses > 100 mg/day) | Meat, vegetables, tree nuts, bananas |
| Vitamin B~7 | Biotin | Water | 30.0 µg | Dermatitis, enteritis | N/D | Raw egg yolk, liver, peanuts, leafy green vegetables | |
| Vitamin B~9 | Folic acid, folinic acid | 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 B12deficiency; other effects. | Leafy vegetables, pasta, bread, cereal, liver |
| Vitamin B~12 | Cyanocobalamin, hydroxocobalamin, methylcobalamin, adenosylcobalamin | Water | 2.4 µg | Pernicious anemia[16] | 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[17] | 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[18] | 1,000 mg | Increased congestive heart failure seen in one large randomized study.[19] | Many fruits and vegetables, nuts and seeds |
| Vitamin K | Phylloquinone, menaquinones | Fat | 120 µg | Bleeding diathesis | N/D | Increases coagulation in patients taking warfarin.[20] | Leafy green vegetables such as spinach, egg yolks, liver |
Health effects
Vitamins are essential for the normal growth and development of a multicellular organism. Using the genetic blueprint inherited from its parents, a fetus begins to develop from the nutrients it absorbs. It requires certain vitamins and minerals to be present at certain times. These nutrients facilitate the chemical reactions that produce among other things, skin, bone, and muscle. If there is serious deficiency in one or more of these nutrients, a child may develop a deficiency disease. Even minor deficiencies may cause permanent damage.[21]
For the most part, vitamins are obtained with food, but a few are obtained by other means. For example, microorganisms in the intestine — commonly known as "gut flora" — produce vitamin K and biotin, while one form of vitamin D is synthesized in the skin with the help of the natural ultraviolet wavelength of sunlight. Humans can produce some vitamins from precursors they consume. Examples include vitamin A, produced from beta carotene, and niacin, from the amino acid tryptophan.[8]
Once growth and development are completed, vitamins remain essential nutrients for the healthy maintenance of the cells, tissues, and organs that make up a multicellular organism; they also enable a multicellular life form to efficiently use chemical energy provided by food it eats, and to help process the proteins, carbohydrates, and fats required for cellular respiration.[4]
