It was towards the end of the 19th century that it was established that adequate and balanced diet needs some other dietary ingredients in addition to carbohydrates, fats, proteins, inorganic salts and water. In 1897 it was shown that the manifestation of beriberi could be controlled by adding rice polishing to the diet in those regions of the world where this disease was widespread. Rice polishing which cured beriberi was isolated and its chemical analysis showed it to have nitrogen in basic form. Therefore it was considered to be an amine. The term vitamin was introduced for such essential dietary constituents (abbreviated from vital amines).

A vitamin is defined as a naturally occurring essential organic constituent of the diet which in minute amounts aids in maintaining the normal metabolic activities of tissues. The presence of an amine group is not essential for a substance to be called a vitamin. The vitamins are chiefly supplied in diet although some vitamins can be synthesized in the body itself in appreciable quantities. For example the amino-acid tryptophan give rise to nicotinic acid. Intestinal bacteria also form some vitamin, e.g. Vitamin K and some B complex vitamins. Vitamin D or cholecalciferol is formed in the skin when exposed to ultra-violet rays.

   Classification of Vitamins

Vitamins are usually classified according to their solubility, i.e. fat soluble vitamins or water soluble vitamins. The fat soluble vitamins are vitamin A, D, E and K while the water soluble vitamins belong ascorbic acid or vitamin C and members of vitamin B complex. In addition, several compounds other than a vitamin may possess the activity of the given vitamin; such compounds are termed Vitamers (from vitamin Isomers)

   Recommended Daily Dietary Allowance of Vitamins

The National Research Council of the U.S.A fixes from time to time the amount of different vitamins and other essential dietary constituents which is recommended to be ingested by individual of various age groups. These allowances are higher than the minimum daily requirements of these dietary ingredients. The following table gives the recommended daily dietary allowance of vitamins

Name of Vitamin New Born Infant Child  8-10 Years Male Adult 22-35 Years Female Adult 22- 45 Years Pregnancy Lactation
Vitamin A (IU) 1500 3500 5000 5000 6000 8000
Vitamin D (IU) 400 400 ..... ..... 400 400
Vitamin E (IU) 5 15 30 25 30 30
Ascorbic Acid (mg) 35 40 60 55 60 60
Thiamine (mg) 0.2 1.1 1.4 1.0 1.1 1.6
Riboflavin (mg) 0.4 1.2 1.7 1.5 1.8 2.0
Nicotinamide (mg) 5 15 18 13 15 20
Pyridoxin (mg) 0.2 1.2 2.0 2.0 2.5 2.5
Folic Acid (mg) 0.05 0.3 0.4 0.4 0.8 0.5
Vitamin B12 1.0 5 5 5 8 6