Introduction

Vitamins are essential organic nutrients required in very small amounts for normal metabolism, growth and physical well-being. Most vitamins are not made in the body, or only in insufficient amounts, and are mainly obtained through food. When their intake is inadequate, vitamin deficiency disorders are the consequence. Vitamins are present in food in minute quantities compared to the macronutrients protein, carbohydrates and fat. The average adult in industrialised countries eats about 600g of food per day on a dry-weight basis, of which less than 1 gram consists of vitamins.

No single food contains all of the vitamins and, therefore, a balanced and varied diet is necessary for an adequate intake. Each of the 13 vitamins known today has specific functions in the body, which makes every one of them unique and irreplaceable. Vitamins are essential for life!

Of the 13 vitamins, 4 are fat-soluble, namely vitamins A, D, E and K. The other vitamins are water-soluble: vitamin C and the B-complex, consisting of vitamins B1, B2, B6, B12, folic acid, biotin, pantothenic acid and niacin.

The history of vitamins can be divided into five periods.

1. The empirical healing of diseases, now associated with vitamin deficiency, through consumption of particular foods. An example is the use of liver to treat night blindness (vitamin A deficiency) by the Egyptians (Papyrus Ebers 1550-1570 BC), Assyrians, Chinese, Japanese, Greeks, Romans, Persians and Arabs.
    
2. The second phase was characterised by the ability to induce a deficiency disease in animals, which started with the classical studies of Lunin and Eijkman around 1890. The ability to produce deficiency diseases, such as beriberi in animals, led to Hopkins’ concept that small amounts of “accessory growth factors” are necessary for growth and life, and the coining of the term “vitamine” in 1912 by the Polish-American scientist, Funk.
    
3. The third phase consisted in seven decades of exciting research involving the discovery, isolation, structure elucidation and synthesis of all the vitamins, and culminating in the synthesis of vitamin B12 in 1972. Most scientists think that the discovery of any new vitamin is quite unlikely, although efforts are still continuing in that quest. Many of the researchers involved in this golden age of the vitamins received a Nobel prize in recognition of their great achievements (Table 2)
    
4. During the era of discovery, a fourth period began which was concerned with the biochemical functions, establishment of dietary requirements and commercial production. In the early 1930s it was realised that riboflavin (vitamin B2) was part of the “yellow enzyme”, which in time led to the elucidation of the role of the B-vitamins as coenzymes. The subsequent identification of most of the B-vitamins as coenzymes remained a central theme, defining their function for many decades. The first commercial synthesis of vitamin C by Reichstein in 1933 was the start of a successful industrial effort that led to the availability of relatively inexpensive vitamins for research and use in animal feedstuffs, for the fortification of food products, and for supplements.
    
5. The accumulation of reports of health benefits beyond preventing deficiencies and exciting new biochemical functions of vitamins ushered in a fifth period, starting with the report in 1955 of the cholesterol-lowering effect of niacin (1). This is now a well accepted effect of the vitamin, which has nothing at all to do with its classical coenzyme role, and is a clear health effect beyond preventing the deficiency disease pellagra.

Finally, work on the biochemical function of vitamins in the last three decades has considerably expanded our concept of how vitamins function in the body and has helped provide a chemical basis for the in vivo observation of their health effects (Table 3).