ABSTRACT
Vitamins or amines of life (from Latin vita = life) are low-molecular bioactive exogenous substances mainly used by mammals as structural-functional domains (cofactors) of complex enzymes that are indispensable for enzyme catalysis. Vitamins are components of food that one needs in very small amounts (daily micrograms or milligrams) for growth, reproduction, and normal functioning; the need for any vitamin is more or less exactly known. Vitamins do not provide energy and do not serve as building blocks of an organism. Animals, including humans, are auxotrophs in relation to most vitamins; they are not able to synthesize vitamins, hence they must import them. e exceptions are the participation of human enteral microora in providing vitamins such as pantothenic acid, niacin, vitamin K, and so forth, and the synthesis of vitamin D3 in skin cells with the help of UV-radiation. If the food contains a sucient amount of carotene, then humans are able to synthesize vitamin A from this provitamin. It is more correct to say that humans receive the necessary vitamins through their gastrointestinal tract.
