A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. The term vitamin was derived from "vitamine", a combination of the words 'vital' and 'amine', because it was suggested that the micronutrients (organic nutrients needed throughout life in small quantities) in food which prevented beriberi and perhaps other similar dietary-deficiency diseases, might be chemical amines. There are two types:

  • Fat-soluble vitamins (A, D, E and K) are usually found in meat and meat products, animal fat and vegetable oils, dairy products and fish. They are transported around the body in fat, and your body stores any excess in the liver and fatty tissues. This means you don't need to get them from food sources every day.
  • Water-soluble vitamins (B, C, folic acid) are found in meat, fish, fruit, vegetables and wholegrains. They are transported around the body in water. This means your body can't store them because you pass the excess through urine. You need to eat foods containing these vitamins every day. Water-soluble vitamins can be destroyed by cooking, so steam and grill rather than boil.

This however, proved incorrect for the micronutient class, and the word was shortened.

Today, a chemical compound is called a vitamin when it cannot 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, K and biotin are required in the human diet only in certain circumstances.

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 are otherwise required less often.

We all need vitamins to live a long and healthy life, and a varied diet is essential if we are to obtain the nutrients we need. Lots of foods naturally contain vitamins, and some popular foods such as breakfast cereals are fortified with vitamins and minerals. That said, it is not always easy: fruit and vegetables age (an apple in a bowl loses vitamins hour by hour), and modern processing techniques have considerably reduced the vitamin and mineral content of many foods. Try to eat a wide variety of fresh foods. Frozen vegetables are also a good option: they can often contain more vitamins than vegetables stored for a long time at room temperature.

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 are 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 convertable to the active form of the vitamin in the body, and are sometimes inter-convertable to one another, as well.

Vitamins have diverse biochemical functions. Some have hormone-like functions as regulators of mineral metabolism (e.g. vitamin D), or regulators of cell and tissue growth and differentiation (e.g. some forms of vitamin A). Others function as antioxidants (e.g. vitamin E and sometimes vitamin C). The largest number of vitamins (e.g. B complex vitamins) function as precursors for enzyme cofactors, that 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. Alternately, vitamins may also be less tightly bound to enzyme catalysts as coenzymes, detachable molecules which function to carry chemical groups or electrons between molecules. For example, folic acid carries various forms of carbon group – methyl, formyl and methylene - in the cell. Although these roles in assisting enzyme-substrate reactions are vitamins' best-known function, the other vitamin functions are equally important.

Too little of just one vitamin may disturb the body's balance and cause health problems. But taking too many vitamins can also be dangerous. This is especially true of the fat-soluble vitamins A, D, E and K because it's harder for the body to get rid of any excess through urine - the most common way to eliminate waste products.

Until the 1900s, 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. New vitamins are discovered occasionally, but we know of the following: A, B1, B2, B3, B5, B6, B10, B11, B12, B13, B15, B17, C, D, E, F, G, H, K, L, M, P, T and U.

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 is 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 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.

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 respiration.

Most vitamin supplements have been extracted from natural foods.
Vitamin A comes from fish-liver oil.
Vitamin B comes from yeast or liver.
Vitamin C is often extracted from small berries in roses.
Vitamin E is extracted from soy beans or maize.
Vitamins may also be synthetically manufactured, but synthetic vitamins are not always as effective as their naturally-derived equivalent.

Vitamins and minerals are two completely different things: minerals help the vitamins work.

The 10 most important minerals are:

  • calcium
  • iodine
  • iron
  • magnesium
  • phosphorus
  • copper
  • manganese
  • chromium
  • selenium
  • zinc.

There is a specific recommended daily allowance (RDA) for most minerals and vitamins.

Vitamin EU RDA
Vitamin A 800mcg
Vitamin B1 1.4mg
Vitamin B2 1.6mg
Vitamin B6 2mg
Vitamin B12 1mcg
Vitamin C 60mg
Vitamin D 5mcg
Vitamin E 10mg
Folic acid 200mcg
Calcium 800mg
Iodine 150mcg
Iron 14mg
Magnesium 300mg
Phosphorus 800mg
Zinc 15mg

Because human bodies do not store most vitamins, humans must consume them regularly to avoid deficiency. The way the human body stores different vitamins varies widely; vitamins A, D, and B12 are stored in significant amounts in the human body, mainly in the liver, and an adult human's diet may be deficient in vitamins A and B12 for many months 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. Deficiencies of vitamins are classified as either primary or secondary. A primary deficiency occurs when an organism does not get enough of the vitamin in its food. 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 use of the vitamin. People 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.

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 to common foods, often called fortification. In addition to these classical vitamin deficiency diseases, some evidence has also suggested links between vitamin deficiency and a number of different disorders.

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).

The best time to take vitamins is during the day, after a meal. Never take supplements on an empty stomach - they will quickly pass out in your urine. This is especially true for the B and C vitamins that dissolve in water. The fat-soluble vitamins A, D, E and K can be stored in the body for up to 24 hours and are sometimes stored in the liver for even longer.

Like most scientific information the above is subject to change, but was correct at the time of writing.

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