Vitamins are classified into two groups depending upon their solubility in water or fat. (i) Fat soluble vitamins : Vitamins which are soluble in fats and oils but insoluble in water are kept in this group. These are vitamins A, D, E and K. They are storedin liver and adipose (fat storing) tissues. (ii) Water soluble vitamins : B group vitamins and vitamin C are soluble in water so they are grouped together. Water soluble vitamins must be supplied regularly in diet because they are readily excreted inurine and cannot be stored (except vitamin $B_{12}$) in our body. Vitamin K is responsible for coagulation of blood.