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

Fat soluble vitamins: Vitamins which are soluble in fat and oils but insoluble in water are kept in this group. These are vitamins $\mathrm{A}, \mathrm{D}, \mathrm{E}$ and $\mathrm{K}$. They are stored in liver and adipose (fat storing) tissues.

Water soluble vitamins: $\mathrm{B}$ group vitamins and vitamin $\mathrm{C}$ are soluble in water. Water soluble vitamins must be supplied regularly in diet because they are readily excreted in urine and cannot be stored (except vitamin ${\mathrm{B}}_{12}$) in our body.