I take Vitamin C when I have a cold. It's a great in food and dietary supplements. How about you?
I usually do take it when I have a cold. I try to take some every day but forget sometimes
Good call! There is evidence it helps shorten the length of colds!
Has there been a lot of studies on it?
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
"Turkestan salt is another thing I require. I need it when I take Cold-Food Powder."; and a lament over their 26-year separation says, "Of late, I have been missing you more than I can say. I have been taking Cold-Food Powder for a long time, but I am still weak."
The Jin Dynasty Daoist scholar Ge Hong's (c. 320) "Baopuzi" ("[Book of the] Master Who Embraces Simplicity") contains invaluable details about the