Все витамины (Vitamins)

The vitamins are organic substances present in the food of the same order of chemical complexity as the natural hormones. They are not used as a sourse of energy, but are needed in appropriate(usually very small) amounts for the carrying out of specific bodily functions and consequently for the maintenance of normal bodily health.
Vitamin A.A closely related substance is B-carotene which is readily transformed. The liver of most animals into two molecules of vitamin A. In man carotene is not well absorbed so that in practice the nutritional value of the carotene of the diet is about half that of equivalent amounts of the vitamin.