`=>` It has been observed that certain organic compounds are required in small amounts in our diet but their deficiency causes specific diseases. These compounds are called vitamins.

`=>` Most of the vitamins cannot be synthesised in our body but plants can synthesise almost all of them, so they are considered as essential food factors.

`=>` However, the bacteria of the gut can produce some of the vitamins required by us.

`=>` All the vitamins are generally available in our diet.

`=>` Different vitamins belong to various chemical classes and it is difficult to define them on the basis of structure.

`=>` They are generally regarded as organic compounds required in the diet in small amounts to perform specific biological functions for normal maintenance of optimum growth and health of the organism.

`=>` Vitamins are designated by alphabets `color{red}(A, B,C, D)`, etc.

● Some of them are further named as sub-groups e.g. `color{red}(B_1, B_2, B_6, B_(12))`, etc.

`=>` Excess of vitamins is also harmful and vitamin pills should not be taken without the advice of doctor.

`=>` The term “Vitamine” was coined from the word vital + amine since the earlier identified compounds had amino groups.

● Later work showed that most of them did not contain amino groups, so the letter ‘e’ was dropped and the term vitamin is used these days.

Vitamins are classified into two groups depending upon their solubility in water or fat.

(i) `color{green}("Fat Soluble Vitamins ")` : Vitamins which are soluble in fat and oils but insoluble in water are kept in this group.

● These are vitamins `color{red}(A, D, E)` and `color{red}(K)`. They are stored in liver and adipose (fat storing) tissues.

(ii) `color{green}("Water Soluble Vitamins ")` : `color{red}(B)` group vitamins and vitamin `color{red}(C)` are soluble in water so they are grouped together.

● Water soluble vitamins must be supplied regularly in diet because they are readily excreted in urine and cannot be stored (except vitamin `color{red}(B_(12))`) in our body.

`=>` Some important vitamins, their sources and diseases caused by their deficiency are listed in Table 14.3.