Vitamins may be regarded as organic compounds required in the diet in small amounts to perform specific biological functions for normal maintenance of optimum growth and health of the organism. They are required in trace amounts and must be obtained from the diet because they are not synthesized in the body.
It is defined as an organic compound and a vital nutrient that an organism requires in limited amounts. An organic chemical compound (or related set of compounds) is called a vitamin when the organism cannot synthesize the compound in sufficient quantities, and must be obtained through the diet.
However, it 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.
Thus, the term is conditional both upon circumstances and particular organism. For example, ascorbic acid (vitamin C) is a vitamin for humans, but not for most other animal organisms. Supplementation is important for the treatment of certain health problems, but there is little evidence of nutritional benefit when used by otherwise healthy people.
All natural vitamins are organic food substances found only in living things (plants and animals). With few exceptions, human body cannot manufacture or synthesize vitamins. They must be supplied by the diet or in dietary supplements. Though most of them are present in diet, some are present as precursors. These precursor forms of vitamins are called as provitamins, which are converted to vitamins. They can be either fat soluble or water soluble.
Thus, each “vitamin” may refer to several 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 like retinal, retinol, and many carotenoids. They are often inter-converted in the body.
Vitamins have various functions. They are necessary for growth, maintenance and reproduction, vitality, health, general well-being, and for the prevention and cure of many health problems and diseases. They improve immunity, prevent illnesses, slower aging process etc. However, they are not used for energy production.
Classification of vitamins are based upon its biological and chemical properties. Altogether there as 13 different types of vitamins required for human body.