I have heard that it is beneficial to take vitamin C when you are experiencing cold symptoms.
I don't know there is any actual evidence that it works for colds, but it does prevent scurvy.
What exactly is scurvy?
Scurvy
Scurvy is a disease resulting from a lack of vitamin C (ascorbic acid). Early symptoms of deficiency include weakness, feeling tired, and sore arms and legs. Without treatment, decreased red blood cells, gum disease, changes to hair, and bleeding from the skin may occur. As scurvy worsens there can be poor wound healing, personality changes, and finally death from infection or bleeding.
It takes at least a month of little to no vitamin C in the diet before symptoms occur. In modern
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