Vitamin
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- For the record label, see Vitamin Records
Vitamins are nutrients required in tiny amounts for essential metabolic reactions in the body.[1] The term vitamin does not include other essential nutrients such as dietary minerals, essential fatty acids, or essential amino acids, nor does it encompass the large number of other nutrients that promote health but that are not essential for life.
Vitamins are bio-molecules that act both as catalysts and substrates in chemical reactions. When acting as a catalyst, vitamins are bound to enzymes and are called cofactors. (For example, vitamin K forms part of the proteases involved in blood clotting.) Vitamins also act as coenzymes to carry chemical groups between enzymes. (For example, folic acid carries various forms of carbon groups–methyl, formyl or methylene–in the cell.)
Until the 1900s, vitamins were obtained solely through food intake. Many food sources contain different ratios of vitamins. Therefore, if the only source of vitamins is food, changes in diet will alter the types and amounts of vitamins ingested. However, as many vitamins can be stored by the body, short-term deficiencies (which, for example, could occur during a particular growing season) do not usually cause disease.
Vitamins have been produced as commodity chemicals and made widely available as inexpensive pills for several decades,[2] allowing supplementation of the dietary intake.
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[edit] History
The value of eating certain foods to maintain health was recognized long before vitamins were identified. The ancient Egyptians knew that feeding a patient liver would help cure night blindness, an illness now known to be caused by a vitamin A deficiency. In 1747, the Scottish surgeon James Lind discovered that citrus foods helped prevent scurvy, a particularly deadly disease in which collagen is not properly formed, and which is characterized by poor wound healing, bleeding of the gums, and severe pain.[3] In 1753, Lind published his Treatise on the Scurvy, which recommended using lemons and limes to avoid scurvy, which was adopted by the British Royal Navy. This led to the nickname Limey for sailors of that organization. Lind's discovery, however, was not widely accepted by individuals in the Royal Navy's Arctic expeditions in the 19th century, where it was widely believed that scurvy could be prevented by practicing good hygiene, regular exercise, and by maintaining the morale of the crew while on board, rather than by a diet of fresh food.[3] As a result, Arctic expeditions continued to be plagued by scurvy and other deficiency diseases. In the early 20th century, when Robert Falcon Scott made his two expeditions to the Antarctic the prevailing medical theory was that scurvy was caused by "tainted" canned food.[3]
In 1881, Russian surgeon Nikolai Lunin studied the effects of scurvy while at the University of Tartu in present-day Estonia.[4] He fed mice an artificial mixture of all the separate constituents of milk known at that time, namely the proteins, fats, carbohydrates, and salts. The mice that received only the individual constituents died, while the mice fed by milk itself developed normally. He made a conclusion that "a natural food such as milk must therefore contain, besides these known principal ingredients, small quantities of unknown substances essential to life".[4] However, his conclusions were rejected by other researchers when they were unable to reproduce his results. One difference was that he had used table sugar (sucrose), while other researchers had used milk sugar (lactose) that still contained small amounts of vitamin B.
In 1897, Christiaan Eijkman discovered that eating unpolished rice instead of the polished variety helped to prevent the disease beriberi. The following year, Frederick Hopkins postulated that some foods contained "accessory factors"—in addition to proteins, carbohydrates, fats, et cetera—that were necessary for the functions of the human body.[3] Hopkins was awarded the 1929 Nobel Prize for Physiology or Medicine with Christiaan Eijkman for their discovery of several vitamins.
The Polish biochemist Kazimierz Funk was the first to isolate the water-soluble complex of micronutrients–the bioactivity of which Fletcher had identified–and proposed the complex be named "Vitamine" in 1912.[5] The name soon became synonymous with Hopkins's "accessory factors", and by the time it was shown that not all vitamins were amines, the word was already ubiquitous. In 1920, Jack Cecil Drummond proposed that the final "e" be dropped to deemphasize the "amine" reference after the discovery that vitamin C had no amine component.
Throughout the early 1900s, the use of deprivation studies allowed scientists to isolate and identify a number of vitamins. Initially, lipid from fish oil was used to cure rickets in rats, and the fat-soluble nutrient was called "antirachitic A". The irony here is that the first "vitamin" bioactivity ever isolated, which cured rickets, was initially called "vitamin A", the bioactivity of which is now called vitamin D,[6] What we now call "vitamin A" was identified in fish oil because it was inactivated by ultraviolet light.
In 1931, Albert Szent-Györgyi and a fellow researcher Joseph Svirbely determined that "hexuronic acid" was actually vitamin C and noted its anti-scorbutic activity. In 1937, Szent-Györgyi was awarded the Nobel Prize for his discovery. In 1943 Edward Adelbert Doisy and Henrik Dam were awarded the Nobel Prize for their discovery of vitamin K and its chemical structure.
[edit] Human vitamins
Vitamins are classified as either water-soluble, meaning that they dissolve easily in water, or fat-soluble, and are absorbed through the intestinal tract with the help of lipids. Each vitamin is typically used in multiple reactions and, therefore, most have multiple functions.[7]
In humans there are thirteen vitamins, divided into two groups; four fat-soluble vitamins (A, D, E and K), and nine water-soluble vitamins (eight B vitamins and vitamin C).
| Vitamin name | Chemical name | Solubility | Deficiency disease | Overdose disease | Recommended Dietary Allowances (male, age 19–70)[8] |
Upper Intake Level (UL/day)[8] |
|---|---|---|---|---|---|---|
| Vitamin A | Retinoids (retinol, retinoids and carotenoids) |
Fat | Night-blindness and Keratomalacia[9] |
Hypervitaminosis A | 900 µg | 3,000 µg |
| Vitamin B1 | Thiamine | Water | Beriberi | ? | 1.2 mg | N/D[10] |
| Vitamin B2 | Riboflavin | Water | Ariboflavinosis | ? | 1.3 mg | N/D |
| Vitamin B3 | Niacin | Water | Pellagra | ? | 16.0 mg | 35.0 mg |
| Vitamin B5 | Pantothenic acid | Water | Paresthesia | ? | 5.0 mg[11] | N/D |
| Vitamin B6 | Pyridoxine | Water | Anemia[12] | ? | 1.3-1.7 mg | 100 mg |
| Vitamin B7 | Biotin | Water | None identified | ? | 30.0 µg | N/D |
| Vitamin B9 | Folic acid | Water | Deficiency during pregnancy is associated with birth defects, such as neural tube defects | ? | 400 µg | 1,000 µg |
| Vitamin B12 | Cyanocobalamin | Water | Megaloblastic anaemia[13] | ? | 2.4 µg | N/D |
| Vitamin C | Ascorbic acid | Water | Scurvy | (Refer to Vitamin C megadosage) | 90.0 mg | 2,000 mg |
| Vitamin D | Ergocalciferol and Cholecalciferol |
Fat | Rickets and Osteomalacia | Hypervitaminosis D | 5.0 µg-10 µg[14] | 50 µg |
| Vitamin E | Tocopherol and Tocotrienol |
Fat | Deficiency is very rare; mild hemolytic anemia in newborn infants.[15] | ? | 15.0 mg | 1,000 mg |
| Vitamin K | Naphthoquinone | Fat | Bleeding diathesis | ? | 120 µg | N/D |
[edit] Vitamins in nutrition and disease
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, at the moment of conception, from the nutrients it absorbs. The developing fetus 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 have the potential to cause permanent damage.[16]
For the most part, vitamins are obtained through food sources. However, a few vitamins 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 natural ultraviolet in sunlight. Humans can produce some vitamins from precursors they consume. Examples include vitamin A, which can be 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 eaten, and to help process the proteins, carbohydrates, and fats required for respiration.
[edit] Vitamin deficiencies
Deficiencies of vitamins are classified as either primary or secondary. A primary deficiency occurs when you do not get enough of the vitamin in the food you eat. A secondary deficiency may be due to an underlying disorder that prevents or limits the absorption or use of the vitamin, due to a “lifestyle factor”, such as smoking, excessive alcohol consumption, or the use of medications that interfere with the absorption or the body's use of the vitamin.[15] Individuals who eat a varied diet are unlikely to develop a severe primary vitamin deficiency. In contrast, restrictive diets have the potential to cause prolonged vitamin deficits, which may result in often painful and potentially deadly diseases.
Because humans do not store most vitamins in their bodies, a human must consume them regularly to avoid deficiency. Human corporeal stores for different vitamins vary widely; vitamins A, D, and B12 are stored in significant amounts in the human body, mainly in the liver,[15] and an adult human may be deficient in vitamin A and B12 for long periods of time before developing a deficiency condition. Vitamin B3 is not stored in the human body in significant amounts, so stores may only last a couple of weeks.[9][15]
Well-known human vitamin deficiencies involve thiamine (beriberi), niacin (pellagra), vitamin C (scurvy) and vitamin D (rickets). In much of the developed world, such deficiencies are rare; this is due to (1) an adequate supply of food; and (2) the addition of vitamins and minerals, often called fortification, to common foods.[8][15]
[edit] Vitamin side effects and overdose
In large doses some vitamins have documented side effects. Vitamin side effects tend to increase in severity with increasing dosage. The likelihood of consuming too much of any vitamin from food is remote, but overdosing from vitamin supplementation does occur. At high enough dosages some vitamins cause side effects, such as nausea, diarrhea, and vomiting.[17][9] Unlike some of the side effects caused by drugs, vitamin side effects rarely cause any permanent harm.[18] When vitamin side effects emerge, recovery is often accomplished by reducing the dosage. Furthermore, the concentrations of vitamins an individual can tolerate vary widely, and appear to be related to age and state of health.[19] In the United States, overdose exposure to all formulations of vitamins was reported by 62,562 individuals in 2004 (nearly 80% of these exposures were in children under the age of 6), leading to 53 “major” life-threatening outcomes and 3 deaths[20]-- a small number in comparison to the 19,250 people who died of unintentional poisoning of all kinds in the U.S. in the same year (2004).[21]
It is for these reasons that physicians and scientists carefully review the clinical data on supplement use in order to determine upper dosage thresholds for each vitamin that can be tolerated as a daily dose by the entire population without side effects. This dosage is known as the tolerable upper intake level (UL).[8]
[edit] Supplements
Dietary supplements, often containing vitamins, are used to ensure that adequate amounts of nutrients are obtained on a daily basis, if optimal amounts of the nutrients cannot be obtained through a varied diet. Scientific evidence supporting the benefits of some dietary supplements is well established for certain health conditions, but others need further study.[22]
Supplements are, as required by law, not intended to treat, diagnose, mitigate, prevent, or cure disease.[22] In some cases, dietary supplements may have unwanted effects, especially if taken before surgery, with other dietary supplements or medicines, or if the person taking them has certain health conditions.[22] Vitamin supplements may also contain levels of vitamins many times higher, and in different forms, than one may ingest through food.[23] Before taking a supplement, it is important to check with a knowledgeable health care provider, especially when combining or substituting supplements with other foods or medicine.
[edit] Governmental regulation of vitamin supplements
Most countries place dietary supplements in a special category under the general umbrella of "foods," not drugs. This necessitates that the manufacturer, and not the government, be responsible for ensuring that its dietary supplement products are safe before they are marketed. Unlike drug products, that must implicitly be proven safe and effective for their intended use before marketing, there are often no provisions to "approve" dietary supplements for safety or effectiveness before they reach the consumer. Also unlike drug products, manufacturers and distributors of dietary supplements are not generally required to report any claims of injuries or illnesses that may be related to the use of their products[24] however, side effects have been reported for several types of vitamin supplements.[25]
[edit] Names in current and previous nomenclatures
The reason the set of vitamins seems to skip directly from E to K is that the vitamins corresponding to "letters" F-J were either reclassified over time, were discarded as false leads, or were renamed because of their relationship to "vitamin B", which became a "complex" of vitamins. 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' 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[26][27] | Chemical name[26][27] | Reason for name change[26] |
|---|---|---|
| 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[28] | Anthranilic acid | No longer classified as a vitamin |
| Vitamin L2[28] | 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 |
[edit] See also
- Nutrition
- Antioxidant
- Dietary supplement
- Dietetics
- Fat soluble vitamins
- Health freedom movement
- Illnesses related to poor nutrition
- Megavitamin therapy
- Orthomolecular medicine
- Pharmacology
- Vitamin poisoning (overdose)
- Whole food supplements
[edit] References
- ^ Lieberman, S, Bruning, N (1990). The Real Vitamin & Mineral Book. NY: Avery Group, 3.
- ^ Kirk-Othmer (1984). Encyclopedia of Chemical Technology Third Edition. NY: John Wiley and Sons, Vol. 24:104.
- ^ a b c d Jack Challem (1997). "The Past, Present and Future of Vitamins"
- ^ a b 1929 Nobel lecture
- ^ Funk, C. and H. E. Dubin. The Vitamines. Baltimore: Williams and Wilkins Company, 1922.
- ^ Bellis, Mary. Vitamins - Production Methods The History of the Vitamins. Retrieved 1 Feb 2005.
- ^ Kutsky, R.J. (1973). Handbook of Vitamins and Hormones. New York:Van Nostrand Reinhold.
- ^ a b c d e Dietary Reference Intakes: Vitamins The National Academies, 2001.
- ^ a b c Vitamin and Mineral Supplement Fact Sheets Vitamin A
- ^ N/D= "Amount not determinable due to lack of data of adverse effects. Source of intake should be from food only to prevent high levels of intake"(see Dietary Reference Intakes: Vitamins).
- ^ Plain 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).
- ^ Vitamin and Mineral Supplement Fact Sheets Vitamin B6
- ^ Vitamin and Mineral Supplement Fact Sheets Vitamin B12
- ^ Value represents suggested intake without adequate sunlight exposure (see Dietary Reference Intakes: Vitamins).
- ^ a b c d e The Merck Manual: Nutritional Disorders: Vitamin Introduction Please select specific vitamins from the list at the top of the page.
- ^ Dr. Leonid A. Gavrilov, Pieces of the Puzzle: Aging Research Today and Tomorrow
- ^ Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. National Academy Press, Washington, DC, 2001.
- ^ Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes: Calcium, Phosphorus, Magnesium, Vitamin D and Fluoride. National Academy Press, Washington, DC, 1999
- ^ Healthier Kids Section: What to take and how to take it.
- ^ 2004 Annual Report of the American Association of Poison Control Centers Toxic Exposure Surveillance System.
- ^ National Center for Health Statistics
- ^ a b c Use and Safety of Dietary Supplements NIH office of Dietary Supplements.
- ^ Jane Higdon Vitamin E recommendations at Linus Pauling Institute's Micronutrient Information Center
- ^ Overview of Dietary Supplements
- ^ Illnesses and Injuries Associated with the Use of Selected Dietary Supplements U. S. FDA Center for Food Safety and Applied Nutrition
- ^ a b c Every Vitamin Page All Vitamins and Pseudo-Vitamins. Compiled by David Bennett.
- ^ a b Vitamins and minerals - names and facts
- ^ a b Michael W. Davidson (2004) Anthranilic Acid (Vitamin L) Florida State University. Accessed 20-02-07
General References Include:
- Stedman's Medical Dictionary. Ed. Maureen Barlow Pugh et.al. 27th ed. Baltimore: Lippincott Williams & Wilkins, 2000.
- Donatelle, Rebecca J. Health: The Basics. 6th ed. San Francisco: Pearson Education, Inc. 2005.
[edit] External links
- USDA RDA chart in PDF format
- Health Canada Dietary Reference Intakes Reference Chart for Vitamins
- NIH Office of Dietary Supplements: Fact Sheets
- NIH Office of Dietary Supplements. Dietary Supplements: Background Information
fat soluble — Retinol (A) | Ergocalciferol and Cholecalciferol (D) | Tocopherol (E) | Naphthoquinone (K)
water soluble — B vitamins (Thiamine (B1), Riboflavin (B2), Niacin (B3), Pantothenic acid (B5), Pyridoxine (B6), Biotin (B7), Folic acid (B9), Cyanocobalamin (B12)) | Choline | Ascorbic acid (C)
Carbohydrates • Colors • Enzymes • Flavors • Food additives • Lipids • Minerals • Proteins • Vitamins • Water
Malnutrition (Kwashiorkor - Marasmus)
other underconsumption- vitamin Vitamin A deficiency (Bitot's spots), Beriberi, Wernicke's encephalopathy, Pellagra, Ariboflavinosis, Scurvy, Osteomalacia
mineral Iron deficiency, Magnesium deficiency - Chromium deficiency
hyperalimentation (Obesity, Hypervitaminosis A, Hypervitaminosis D)
