I know I have to take vitamin C but why actually?
Vitamin C
Vitamin C, also known as ascorbic acid and -ascorbic acid, is a vitamin found in various foods and sold as a dietary supplement. It is used to prevent and treat scurvy. Vitamin C is an essential nutrient involved in the repair of tissue and the enzymatic production of certain neurotransmitters. It is required for the functioning of several enzymes and is important for immune system function. It also functions as an antioxidant. 
Current evidence does not support its use for the prevention of the common cold. There is
early aftermath of September 11th, when I happened to be recounting the pre–September 11th events concerning the Moussaoui investigation to other FBI personnel in other divisions or in FBIHQ, almost everyone's first question was "Why?—Why would an FBI agent(s) deliberately sabotage a case? (I know I shouldn't be flippant about this, but jokes were actually made that the key FBI HQ personnel had to be spies or moles like Robert Hanssen who were actually working for Osama Bin Laden to have so undercut Minneapolis's effort.)