Everything about Vitamins totally explained
A
vitamin is an organic compound required as a
nutrient in tiny amounts by an
organism. A compound is called a vitamin when it can't be
synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on the circumstances and the particular organism. For example,
ascorbic acid functions as
vitamin C for some animals but not others, and
vitamins D and
K are required in the human diet only in certain circumstances.
Vitamins are classified by their biological activity, not their structure. Thus, each "vitamin" actually refers to a number of
vitamer compounds, which form a set of distinct chemical compounds that show the biological activity of a particular vitamin. Such a set of chemicals are grouped under an alphabetized vitamin "generic descriptor" title, such as "vitamin A," which (for example) includes
retinal,
retinol, and many
carotenoids. Vitamers are often inter-convertible in the body. The term
vitamin doesn't 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 are otherwise required less often.
Vitamins have diverse biochemical functions, including function as
hormones (for example vitamin D),
antioxidants (for example vitamin E), and mediators of cell signaling and regulators of cell and tissue growth and differentiation (for example vitamin A). The largest number of vitamins (for example B complex vitamins) function as precursors for enzyme
cofactor bio-molecules (
coenzymes), that help act as
catalysts and
substrates in
metabolism. When acting as part of a catalyst, vitamins are bound to
enzymes and are called
prosthetic groups. For example,
biotin is part of enzymes involved in making
fatty acids. Vitamins also act as
coenzymes to carry chemical groups between enzymes. For example,
folic acid carries various forms of carbon group –
methyl,
formyl and
methylene - in the cell. Although these roles in assisting enzyme reactions are vitamins' best-known function, the other vitamin functions are equally important.
Until the 1800s, vitamins were obtained solely through food intake, and changes in diet (which, for example, could occur during a particular growing season) can alter the types and amounts of vitamins ingested. Vitamins have been produced as commodity chemicals and made widely available as inexpensive pills for several decades, allowing supplementation of the dietary intake.
History
The value of eating a certain food 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
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, wasn't 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. 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."
When the article was translated into German, the translation failed to state that it was a newly discovered nutrient, a claim made in the original Japanese article, and hence his discovery failed to gain publicity. Polish biochemist
Kazimierz Funk isolated the same complex of micronutrients and proposed the complex be named "Vitamine" (a
portmanteau of "vital amine") in 1912. 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.
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's 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 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.
In humans
Vitamins are classified as either
water-soluble, meaning that they dissolve easily in water, or
fat-soluble vitamins, which are absorbed through the
intestinal tract with the help of
lipids (fats). In general, water-soluble vitamins are readily excreted from the body. Each vitamin is typically used in multiple reactions and, therefore, most have multiple functions.
In humans there are 13 vitamins: 4 fat-soluble (A, D, E and K) and 9 water-soluble (8 B vitamins and vitamin C).
In nutrition and diseases
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. 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's serious deficiency in one or more of these nutrients, a child may develop a deficiency disease. Even minor deficiencies may cause permanent damage.
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 natural
ultraviolet in
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.
Side effects and overdose
In large doses, some vitamins have documented side effects that tend to be more severe with a larger 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,
When side effects emerge, recovery is often accomplished by reducing the dosage. The concentrations of vitamins an individual can tolerate vary widely, and appear to be related to age and state of health. 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—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).
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 can't 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. Some research has suggested that supplements don't only provide no tangible health benefits for generally healthy individuals, but may actually increase mortality.
In the United States, advertising for dietary supplements is
required to include a disclaimer that the product isn't intended to treat, diagnose,
mitigate, prevent, or cure disease, and that any health claims have not been evaluated by the
Food and Drug Administration.
Intake of excessive quantities can cause
vitamin poisoning, often due to overdose of
Vitamin A and
Vitamin D (The most common poisoning with multinutrient supplement pills doesn't involve a vitamin, but is rather due to the mineral
iron). Due to toxicity, most common vitamins have recommended upper daily intake amounts.
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're marketed. Unlike drug products, that must explicitly 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.
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, discarded as false leads, or 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 J 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:
Further Information
Get more info on 'Vitamins'.
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