Vitamin A refers to several chemical compounds that have biological functions in all mammals. They are partly ingested directly with food or formed from carotenes (provitamin A), which not all animals are capable of (domestic cats, for example, are not).
As early as 1500 BC, the Chinese used liver and honey to cure night blindness. Vitamin A is important for growth, function and structure of skin and mucous membranes, blood cells, metabolism, as well as for the visual process. The utilization of this vitamin in the body can be disturbed by liver damage and the intake of estrogen preparations.