Vitamin
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Vitamins are nutrients required for essential metabolic reactions in the body catalysts and participants in the chemical reaction. The body typically assembles vitamin-dependent catalysts from a variety of building blocks including amino acids, sugars, phosphates, and vitamins. Each vitamin is typically used in multiple different catalysts and therefore has multiple functionsnervous system maintains a feeling of normalcy across a wide range of vitamin dosages.
Vitamins have only been produced as commodity chemicals and made widely available as inexpensive pills for a few decadeswater soluble, which means they dissolve easily in water, or fat soluble, which means they are absorbed through the intestinal tract with the help of lipids.
As mentioned above, for the most part we rely on food sources to meet our vitamin needs. However, there are a few vitamins that we obtain 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 sunlight.
Some vitamins can also be obtained from precursors which can be obtained in the diet. Examples include vitamin A, which can be produced from beta carotene and niacin from the amino acid tryptophan.
The term vitamin does not encompass other essential nutrients such as dietary minerals, essential fatty acids, or essential amino acids, nor is it used for the large number of other nutrients that merely promote health, but are not strictly essential.
In 1881, Russian surgeon Nikolai Lunin fed mice upon an artificial mixture of all the separate constituents of milk known at that time, namely the proteins, fats, carbohydrates, and salts. They 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" [1929 Nobel lecture] However, his conclusion was rejected by other researchers who were unable to reproduce his results. One difference was that he used table sugar (sucrose), while other researchers used milk sugar (lactose) which still contained small amounts of vitamin B.
In 1905, William Fletcher discovered that eating unpolished rice instead of polished helped prevent the disease beriberi. The following year, Frederick Hopkins postulated that foods contained "accessory factors"—in addition to proteins, carbohydrates, fats, etc.—that are necessary to the human body. When Casimir Funk isolated the water-soluble complex of micronutrients whose bioactivity Fletcher had identified, he proposed that it 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, and the name has been "vitamin" ever since.
The reason the alphabet soup of vitamins seems to skip from E to the rarely-mentioned K is that most of the "letters" were reclassified, as with fatty acids, discarded as false leads, or renamed because of their relationship to "vitamin B", which became a "complex" of vitamins. Vitamin G, Riboflavin, for example, is now known as B2.
Throughout the early 1900s, scientists were able to isolate and identify a number of vitamins by depriving animals of them. 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 vitamine A, this bioactivity is now called vitamin D, which is itself subject to the semantic debate that it is not truly a vitamin because it is a steroid derivative. What we now call "vitamin A" was identified in fish oil because it was inactivated by ultraviolet light. Most of what we now recognize as the water-soluble organic micronutrients were initially referred to as just one entity, "vitamin B".
As the body builds itself according to its genetic plan, it will need certain vitamins and minerals in place at the right times. These nutrients will allow the chemical reactions to take place that will make skin, bone, muscle, etc. out of food.
If those nutrients are missing, the body must manage as best it can to follow its blueprint. If there is serious deficiency, a child develops a deficiency disease and the genetic plan is completed so poorly that the results are obvious - malformed limbs in the case of rickets, or the mental retardation of iodine deficiency.
Once growth and development is completed, adults remain dependent upon vitamins to maintain good health. Vitamins are necessary to maintain proper functioning of the nervous system. Vitamins enable the body to use the calories provided by the food that we eat and to help process proteins, carbohydrates, and fats. Vitamins are also involved in building cells, tissues, and organs - vitamin C, for example, helps produce healthy skin.
Vitamins are classified as fat-soluble or water-soluble based on how they are absorbed by the body. Vitamins A, D, E, and K are fat soluble, while the water-soluble vitamins include vitamin C and the B-complex vitamins (thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), vitamin B6, vitamin B12, biotin and folate.
Research has shown that foods rich in antioxidants are particularly beneficial for health. Antioxidants neutralize free radicals. A buildup of free radicals can damage body cells and tissues, resulting in disease. Studies have shown that diets rich in vegetables and fruits result in a lower incidence of some diseases, including certain cancers.
Well-known vitamin deficiencies are thiamine (beriberi), niacin (pellagra), vitamin C (scurvy) and Vitamin D (rickets). In north America today, however, such deficiencies are rare due to an adequate food supply for most people, and food fortification programs that add vitamins and minerals to common foods.
Scientists now have shifted their focus to discovering ways in which vitamins can promote health, prevent disease, boost the body's protection against infection and even slow down the aging process. At the same time, public interest in vitamins has heightened. This has been prompted by headlines in the media and widespread advertising by the manufacturers of nutrient supplements.
Other nutrients that are not classified as vitamins include:
Fat-soluble vitamins may be stored in the body and can cause toxicity when taken in excess. Water-soluble vitamins are not stored in the body, with the exception of vitamin B12, which is stored in the liver.
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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 characterized by poor wound healing, bleeding of the gums, and severe pain. In 1753, Lind published his Treatise on the Scurvy. His recommendation of using lemons and limes to avoid scurvy was adopted by the British Royal Navy, resulting in the nickname Limey for sailors of that organization. His discovery, however, was not widely accepted by individuals; In the Royal Navy's Arctic expeditions in the 19th century, for example, it was widely believed that scurvy was prevented by good hygiene on board ship, regular exercise, and maintaining the morale of the crew, rather than by a diet of fresh food, so that Navy expeditions took all the amenities of 'sophisticated' society, like silk sheets, spices, expensive food and drink, and almost nothing of any use beyond the Arctic Circle. As a result, these expeditions continued to be plagued by scurvy and other deficiency diseases. At the time Robert
Falcon Scott made his two expeditions to the Antarctic in the early 20th century, the prevailing medical theory was that scurvy was caused by "tainted" canned food.
Human vitamins
In humans, there are thirteen vitamins, divided into two groups, the four fat-soluble vitamins (A, D, E and K) and the nine water-soluble vitamins (eight B vitamins and vitamin C).
Nutrition
Why we need vitamins
Although vitamins contain no calories, they are essential for normal growth and development. Using the genetic blueprint inherited from its parents, a child's body begins to build itself from the "food" it absorbs beginning at the moment of conception. Once out of the womb, the child continues on with this incredibly complex set of tasks using the building blocks it gets by eating and drinking. There is no other source for the raw materials, tools, and energy needed to build an adult human. We are literally made out of what we have eaten throughout our lives.Vitamin deficiencies
Deficiencies of vitamins are either primary or secondary. A primary deficiency occurs because you do not get enough of the vitamin in the food you eat. A secondary deficiency may be due to a lifestyle factor, such as smoking, excessive alcohol consumption, or the use of certain medications that interfere with the absorption or the body's use of the vitamin. Prolonged use of antibiotics will kill off the useful gut flora that make vitamin K. Vitamin deficiencies may also be due to an underlying problem, such as an intestinal disorder, that prevents or limits the absorption or use of the vitamin.Vitamin overdosing
The likelihood of consuming too much of any vitamin from food is remote, but overdosing from vitamin supplementation often occurs.ISBN 0878576789 For example, many people take between 500 and 10,000 mg/day of vitamin C, usually in the belief that this will relieve or "cure" a cold. Ingestion of large enough quantities of vitamin C can cause intestinal gas and loose stool. Further increasing the dose causes painful cramping and diarrhea. The severity of the cramping increases with increasing dose. These intestinal side effects have been reported at doses as low as 500 mg/day. On the other hand, some individuals are known to tolerate more than 50,000 mg/day without intestinal side effectsRobert Cathcart. In very rare cases, doses of vitamin C above 5,000 mg/day are known to cause kidney stonesMassey LK, Liebman M, Kynast-Gales SA.] Ascorbate increases human oxaluria and kidney stone risk, J Nutr. 2005 Jul;135(7):1673-7. and against [Stephen Lawson] What About Vitamin C and Kidney Stones? Linus Pauling Institute Adminstrative Officer] the possibility of this effect.Notes
Some of the vitamins are known by other names in older literature. These names are written after the vitamins in brackets.
Vitamin B2 is also referred to as vitamin G.
Vitamin B7, or biotin is also referred to as "vitamin H."
Vitamin B9, or folic acid and other folates such as "vitamin M" (monkey antianemia factor, pteryl-tri-glutamic acid) are referred to as folicin.
Vitamin B3 is also referred to as "vitamin PP", a name derived from the obsolete term "pellagra-preventing factor". Many other essential dietary substances were originally called vitamins and are now classified differently.
Still others are on the borderline, either candidates for classification as vitamins, or recently classified but widely accepted.
Vitamin deficiency and excess
An organism can survive for some time without vitamins, although prolonged vitamin deficit results in a disease state, often painful and potentially deadly. Body stores for different vitamins can vary widely; an adult may be deficient in vitamins A or B12 for a year or more before developing a deficiency condition, while vitamin B1 stores may only last a couple of weeks.Pseudo-vitamins
Non-human vitamins
Different organisms need different trace organic substances. Most mammals need, with few exceptions, the same vitamins as humans. One notable exception is Vitamin C, which can be synthesized by all other mammals except other higher primates and guinea pigs. The less related a species is to mammals, the more different the organisms' requirements become. For example, some bacteria need adenine. Pyrroloquinoline quinone (PQQ) found in yogurt was reported as a vitamin for mice in 2003.See also
References
External links
Vitamins
All B vitamins | All D vitamins
Retinol (A) | Thiamine (B1) | Riboflavin (B2) | Niacin (B3) | Pantothenic acid (B5) | Pyridoxine (B6) | Biotin (B7) | Folic acid (B9) | Cyanocobalamin (B12) | Ascorbic acid (C) | Ergocalciferol (D2) | Cholecalciferol (D3) | Tocopherol (E) | Naphthoquinone (K)
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