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Vitamin

2007 Schools Wikipedia Selection. Related subjects: Food and agriculture;
General Chemistry

   Retinol (Vitamin A)
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   Retinol (Vitamin A)

   Vitamins are nutrients required in very small amounts for essential
   metabolic reactions in the body . The term vitamin does not include
   other essential nutrients such as dietary minerals, essential fatty
   acids, or essential amino acids. Nor does the term refer to the large
   number of other nutrients that promote health, but are not strictly
   essential.

   Vitamins 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, a seasonal, yearly or even daily
   change in diet also alters the ratio of ingested vitamins. Many
   vitamins can be stored by the body over a range of dosages and short
   term deficiencies (e.g. during a particular food growing season), do
   not always result in disease.

   Vitamins have been produced as commodity chemicals and made widely
   available as inexpensive pills for several decades allowing for
   consistent supplementation to dietary intake.
   Fruits and vegetables are often a good source of vitamins.
   Enlarge
   Fruits and vegetables are often a good source of vitamins.

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, 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 is characterized by poor wound healing, bleeding of the gums, and
   severe pain. 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. 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.

   In 1881, Russian surgeon Nikolai Lunin studied the effects of scurvy
   while at the University of Tartu (in present day Estonia). 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". 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) which 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, etc.—that were necessary for the functions of the human body.
   Hopkins was awarded the 1929 Nobel Prize for Physiology or Medicine,
   with Christiaan Eijkman, for their discovery of several vitamins.

   Kazimierz Funk was the first to isolate the water-soluble complex of
   micronutrients, whose bioactivity Fletcher had identified, and Funk
   proposed the complex be named "Vitamine". The name soon became
   synonymous with Hopkins' "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.
   Riboflavin (Vitamin B2)
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   Riboflavin (Vitamin B[2])

   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, What we now call "vitamin A" was identified in
   fish oil because it was inactivated by ultraviolet light.

   In 1931, Albert Szent-Györgyi and his research fellow Joseph Svirbely,
   determined that "hexuronic acid" was actually vitamin C and noted its
   anti-scorbutic activity, and 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.

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.

   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 Recommended
   Dietary Allowances
   (male, age 19–70)
   Upper Intake Level
   (UL/day)
   Vitamin A Retinoids (include: retinol,
   retinal, retinoic acid,
   3-dehydroretinol and its derivatives) Fat Night-blindness,
   Keratomalacia 900 µg 3,000 µg
   Vitamin B[1] Thiamine Water Beriberi 1.2 mg (N/D)
   Vitamin B[2] Riboflavin Water Ariboflavinosis 1.3 mg N/D
   Vitamin B[3] Niacin Water Pellagra 16.0 mg 35.0 mg
   Vitamin B[5] Pantothenic acid Water Paresthesia 5.0 mg N/D
   Vitamin B[6] Pyridoxine Water Anaemia 1.3-1.7 mg 100 mg
   Vitamin B[7] Biotin Water n/a 30.0 µg N/D
   Vitamin B[9] Folic acid Water Deficiency during pregnancy is associated
   with birth defects. 400 µg 1,000 µg
   Vitamin B[12] Cyanocobalamin Water Megaloblastic anaemia 2.4 µg N/D
   Vitamin C Ascorbic acid Water Scurvy 90.0 mg 2,000 mg
   Vitamin D[2]–D[4] Lumisterol, Ergocalciferol,
   Cholecalciferol, Dihydrotachysterol,
   7-Dehydrocholesterol Fat Rickets 5.0 µg-10 µg 50 µg
   Vitamin E Tocopherol, Tocotrienol Fat deficiency is very rare, mild
   hemolytic anemiain newborn infants 15.0 mg 1,000 mg
   Vitamin K Naphthoquinone (not to be confused with ketamine) Fat
   Bleeding diathesis 120 µg N/D

Vitamins in nutrition and disease

   Vitamins are essential for normal growth and development. 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.

   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. Some vitamins can be
   obtained from precursors that are obtained in the diet. Examples
   include vitamin A, which can be produced from beta carotene and niacin,
   from the amino acid tryptophan.

   Once growth and development are completed, vitamins remain essential
   components of the healthy maintenance of the cells, tissues, and organs
   that make up the human body, and enable the body to efficiently use the
   calories provided by the food that we eat, and to help process
   proteins, carbohydrates, and fats.

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. Individuals who eat a
   varied diet are unlikely to develop a primary vitamin deficiency.
   Whereas, restrictive diets have the potential to cause prolonged
   vitamin deficits, which may result in often painful and potentially
   deadly diseases.

   Because most vitamins are not stored in the body, a person must consume
   them regularly to avoid deficiency. Body stores for different vitamins
   vary widely; vitamins A, D, and B[12] are stored in significant amounts
   in the body, mainly in the liver, and an adult may be deficient in
   vitamin A and B[12] for long periods of time before developing a
   deficiency condition. Vitamin B[3], is not stored in the body in
   significant amounts, and stores may only last a couple of weeks.

   Well-known vitamin deficiencies involve thiamine (beriberi), niacin
   (pellagra), vitamin C (scurvy) and vitamin D ( rickets). In much of the
   developed world, such deficiencies are rare due to; an adequate supply
   of food and the addition of vitamins and minerals, often called
   fortification, to common foods.

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. Unlike some of the side effects caused by drugs, vitamin side
   effects rarely cause any permanent harm. 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.

   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).

Supplements

   Dietary supplements are often used to ensure that adequate amounts of
   nutrients are obtained on a daily basis, if 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.

   Supplements are, as required by law, not intended to treat, diagnose,
   mitigate, prevent, or cure disease. 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. Vitamin supplements may also contain
   levels of vitamins many times higher, and in different forms, than one
   may ingest through food. 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.

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 however, side effects have been reported for
   several types of vitamin supplements.

Names in current and previous nomenclatures

   The reason the set of vitamins seems to skip directly from E to the
   rarely-mentioned 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 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 vitamin
   name Chemical name Current vitamin
   name Reason for name change
   Vitamin B[4] Adenine N/A No longer classified as a vitamin
   Vitamin B[8] Adenylic acid N/A No longer classified as a vitamin
   Vitamin F Essential fatty acids N/A Needed in large quantaties,
   does not fit definition of vitamin.
   Vitamin G Riboflavin Vitamin B[2] Reclassified as B-complex
   Vitamin H/ Vitamin I Biotin Vitamin B[7] Reclassified as B-complex
   Vitamin J Catechol, Flavin N/A No longer classified as a vitamin
   Vitamin L[1] Orthoaminobenzoic acid,
   Anthranilic acid N/A No longer classified as a vitamin
   Vitamin L[2] Adenyl thiomethylpentose N/A No longer classified as a
   vitamin
   Vitamin M Folic acid Vitamin B[9] Reclassified as B-complex
   Vitamin P Flavonoids N/A No longer classified as a vitamin
   Vitamin PP Niacin Vitamin B[3] Reclassified as B-complex
   Vitamin R, Vitamin B[10] Pteroylmonoglutamic acid N/A No longer
   classified as a vitamin
   Vitamin S, Vitamin B[11] Pteroylheptaglutamic acid N/A No longer
   classified as a vitamin
   Vitamin U Allantoine N/A No longer classified as a vitamin

   Retrieved from " http://en.wikipedia.org/wiki/Vitamin"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
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