DEFINITION OF VITAMINS
The vitamin concept has undergone extensive revisions during the history of biochemistry. However, Franz Holfmeister's definition- vitamins are substances which are indispensable for the growth and maintenance of the animal organism, which occur both in animals and plants and are present in only small amounts in food'-still holds good, although it has been interpreted in various ways.
The term 'vitamin', in its modern sense, usually refers to the substances distinct from major components of food, required in minute quantities and whose absence causes specific deficiency diseases. As the living organisms cannot synthesize most of these compounds, a steady supply of them is quo non life. Their ultimate source is the plant or world.
Differences with hormones- Indeed, for some time, it was believed that the distinction between vitamins and hormones was no longer tenable. But there exists a fundamental difference between these two classes of active substances: the hormones are regulatory substances where as the vitamins are accessory nutrients. The vitamins also differ from the hormones in that they are supplied to the body from external source where as hormones are synthesized within some part of the body of an organism. Moreover, most vitamins and some hormones are involved either directly or indirectly in enzyme systems in order to carry out biochemical functions. Some vitamins are also known to be co enzymes.
General Characters of Vitamins
The vitamins are characterized for some general facts, which are listed below:
- Vitamins are of widespread occurrence in nature, both in plant and animal worlds.
- All common foodstuffs contain more than one vitamin.
- The plants can synthesize some vitamins where as only few vitamins are synthesized in the animals.
- Human body can synthesize some vitamins, e.g., vitamin A is synthesized from its precursor carotene and vitamin D from ultraviolet irradiation of ergosterol and 7-dehydrocholersterol. Some members of the vitamin B complex are synthesized by microorganisms present in the intestinal tract. Vitamin C is also synthesized in some animals such as rat.
- Most of vitamins have been artificially synthesized.
- All the cells of the body store vitamins to some extent.
- Vitamins are partly destroyed and are partly excreted.
- Vitamins are non antigenic.
- Vitamins carry out fractions in very low concentrations. Hence, the total daily requirement is very small.
- Vitamins are effective when take orally.
- Synthetically- made vitamins are just as nutritionally good as natural vitamins.
- Old people need about the same amounts of vitamins as young people.