(i) Vitamins are a group of heterogeneous compounds of which each is essential for proper operation of various processes in the body.
(ii) These are main six types of vitamins Eg. A,B,C, D, E and K.
(iii) Out of these A, D, E and K are fat soluble whereas B and C are water soluble.
(iv) Vitamins like riboflavin (vitamin B,) and nicotinamide (vitamin B) are necessary for production of FADH, and NADH, respectively which are produced in processes like glycolysis and Kreb's cycle.