Introduction

Abstract

The vitamins consist of a mixed group of chemical substances, designated as vitamins not by their chemical characteristics but by their function. They are organic constituents of the diet, essential for the well-being of the animal body and ingested in small amounts. However, the application of the definition is somewhat arbitrary, for some organic compounds, e.g. the essential fatty acids are not usually regarded as vitamins, while some vitamins, e.g. vitamin D, are predominantly synthesized by the body and could be better regarded as pro-hormones. Hence the definition stems from historical rather than current considerations.