Vitamins for optimum health

All living things, plant or animal, need vitamins for health, growth, and reproduction. They use vitamins as tools in processes that regulate chemical activities in the organism and that use basic food elements carbohydrates, fats, and proteins to form tissues and to produce energy.

Most vitamins are essential in the diet because the body does not produce enough of them or, in many cases, does not produce them at all. Many different vitamins have been identified by nutritionists: A, eight B-complex vitamins, C, D, E, and others. Some substances, such as carnitine and choline, behave like vitamins but are made in adequate amounts in the human body.

Vitamins were originally placed in categories based on their function in the body and were given letter names. Later, as their chemical structures were revealed, they were also given chemical names. Today, both naming conventions are used.

History
The value of certain foods in maintaining optimum health was recognized long before the first vitamins were actually identified. In the 18th century, for example, it had been demonstrated that the addition of citrus fruits to the diet would prevent the development of scurvy. In the 19th century it was shown that substituting unpolished for polished rice in a rice-based diet would prevent the development of beriberi.

In 1906 the British biochemist Frederick Hopkins demonstrated that foods contained necessary accessory factors in addition to proteins, carbohydrates, fats, minerals, and water. In 1911 the Polish chemist Casimir Funk discovered that the anti-beriberi substance in unpolished rice was an amine, so Funk proposed that it be named vitamine for vital amine. It was later discovered that many vitamins do not contain amines at all. Because of its widespread use, Funk's term continued to be applied, but the final letter e was dropped.

In 1912 Hopkins and Funk advanced the vitamin hypothesis of deficiency, a theory that postulates that the absence of sufficient amounts of a particular vitamin in a system may lead to certain diseases. During the early 1900s, through experiments in which animals were deprived of certain types of foods, scientists succeeded in isolating and identifying the various vitamins recognized today.

How Vitamins Work
In the body, proteins, carbohydrates, and fats combine with other substances to yield energy and build tissues. These chemical reactions are catalyzed, or accelerated, by enzymes produced from specific vitamins, and they take place in specific parts of the body. The vitamins needed by humans are divided into two categories: water-soluble vitamins (the B vitamins and vitamin C) and fat-soluble vitamins (A, D, E, and K).

The water-soluble vitamins are absorbed by the intestine and carried by the circulatory system to the specific tissues. When a person takes in more water-soluble vitamins than are needed, small amounts are stored in body tissue, but most of the excess is excreted in urine. Because water-soluble vitamins are not stored in the body in appreciable amounts, a daily supply is essential to prevent depletion.

Fat-soluble vitamins seem to have highly specialized functions. The intestine absorbs fat-soluble vitamins, and the lymph system carries these vitamins to the different parts of the body. Fat-soluble vitamins are involved in maintaining the structure of cell membranes and also are responsible for the synthesis of certain enzymes. The body can store larger amounts of fat-soluble vitamins than of water-soluble vitamins. The liver provides the chief storage tissue for vitamins A and D, while vitamin E is stored in body fat and to a lesser extent in reproductive organs. Relatively little vitamin K is stored. Excessive intake of fat-soluble vitamins, particularly vitamins A and D, can lead to toxic levels in the body.

Many vitamins work together to regulate several processes within the body. A lack of vitamins or a diet that does not provide adequate amounts of certain vitamins can upset the body's internal balance or block one or more metabolic reactions.

Daily Requirements
With a few exceptions, the body is unable to make vitamins; they must be supplied in the daily diet or through supplements. One exception is vitamin D, which can be produced in the skin when the skin is exposed to sunlight. Another exception is vitamin K, that is not made by the human body but is formed by microorganisms that normally flourish in the intestinal tract only when green, leafy vegetables and vegetable oils are ingested.

The body's vitamin requirements are expressed in terms of recommended dietary allowances, or RDA. These allowances are the amount of essential nutrients that, if acquired daily, are considered to be sufficient to meet the known nutritional needs of most healthy persons.

The strength of a vitamin or the amount of the vitamin necessary to produce a certain effect in the body is often expressed in terms of international units, abbreviated IU. The unit corresponds to a weight of the purified vitamin, and its value differs from one vitamin to another. The strength of a vitamin is also generally expressed directly in metric weights micrograms or milligrams.

Sources of Vitamins
Vitamins, though they are available from a variety of sources, are unevenly distributed in natural sources. For example, some vitamins, such as vitamin D, are produced only by animals, whereas other vitamins are found only in plants. All vitamins can be synthesized from foods and other sources, and there is no evidence that natural vitamins are superior to those that are synthetically derived.

Some foods are fortified with vitamins that is, vitamins that are not normally present in the food, or that have been removed during processing, are added to the food before it is sold. Milk, for example, is fortified with vitamin D, and vitamins that have been lost from flour during processing are often replaced.

Although vitamin supplements are generally unnecessary for otherwise well-nourished persons, there are times when the body's vitamin requirements may increase and when vitamin supplements may be essential for optimum health. Those include pregnant women, the elderly, and the chronically ill. You can find large selection of high quality and low priced supplemental vitamins HERE and HERE. Excessive intakes of supplemental vitamins should be avoided, however, because of the possibility of toxicity.