Ultimately, it was the chemists who isolated the various vitamins, deduced their chemical structure and developed methods for the synthesis of vitamins. These organic compounds are found in very small quantities in foods and are essential for normal functioning and survival. Humans can synthesize certain vitamins to a certain extent, such as vitamin D when the skin is exposed to sunlight, niacin from the amino acid tryptophan, and vitamin K and biotin from bacteria in the intestine. However, humans usually rely on their diet for the supply of vitamins.
When a vitamin is scarce or cannot be used properly, a specific deficiency syndrome occurs. When the vitamin deficiency is replenished before irreversible damage occurs, the signs and symptoms are reversed. The amounts of vitamins in foods and the amounts required daily are measured in milligrams and micrograms. Vitamins and minerals are micronutrients that our bodies need to perform a number of normal functions.
However, these micronutrients are not produced in our bodies and must be derived from the foods we eat.
Water-soluble vitamins(vitamin C and B-complex vitamins, such as vitamin B6, vitamin B12 and folate) must be dissolved in water before they can be absorbed by the body and therefore cannot be stored. Multivitamins can play an important role when nutritional requirements are not met by diet alone. The vitamins and minerals that are part of enzymes are called coenzymes and cofactors, respectively.
The puzzle of each vitamin was solved through the work and contributions of epidemiologists, physicians, physiologists and chemists. Biotin (water-soluble vitamin) is needed as a coenzyme in the citric acid cycle and in lipid metabolism. In the 19th century, vitamin B deficiencies affected many people in North America but are now rare in the United States. Choline is a dietary component similar to vitamins that is clearly necessary for normal metabolism, but which the body can synthesize.
To maximize vitamin B absorption, fruits and vegetables should not be stored for long periods of time, should be consumed more as whole foods, and vegetables should be steamed rather than boiled. Biotin deficiency is very rare and symptoms of deficiency are similar to those of other B vitamins, such as weakness, but may also include hair loss when it is severe, a rash around the eyes, nose and mouth, depression, lethargy and hallucinations. Fat-soluble vitamins, on the other hand, are found in association with fats and oils in food and in the body and generally require carrier proteins for transport through the body's water-filled compartments. Unlike complex organic compounds (carbohydrates, lipids, proteins, vitamins) discussed earlier, minerals are simple inorganic elements often found in salt form in the body that are not metabolized on their own nor do they provide energy. Niacin is used to lower blood cholesterol levels; vitamin D is used to treat psoriasis; and pharmacological derivatives of vitamin A are used to treat acne and other skin conditions as well as reduce skin wrinkles.
The 13 vitamins known to be required by humans are classified into two groups based on their solubility. Coenzyme A is also involved in the synthesis of lipids, cholesterol and acetylcholine (a neurotransmitter). Although some marketers claim that taking a vitamin containing a thousand times the daily value of certain B vitamins increases energy and performance, this is a myth that is not supported by science. Unlike macronutrients, vitamins do not serve as a source of energy for the body nor do they provide raw materials for tissue formation.