I like to take vitamin C whenever I'm cold. It's also known as ascorbic acid
How does vitamin C help when you are cold?
It's usually shortening the length of my colds! There is scientific evidence that's what it helps with.
Is it possible to take too much vitamin C?
I believe too much Vitamin C can cause diarrhea. But taken the right way works as an antioxidant.
I think orange juice is a good source of vitamin c.
, and strawberries. Prolonged storage or cooking may reduce vitamin C content in foods. 
Biology.
Biology Significance.
Vitamin C is an essential nutrient for certain animals including humans. The term "vitamin C" encompasses several vitamers that have vitamin C activity in animals. Ascorbate salts such as sodium ascorbate and calcium ascorbate are used in some dietary supplements. These release ascorbate upon digestion. Ascorbate and ascorbic acid are both naturally present in the body, since the forms interconvert according to pH. Oxidized forms of the molecule such as
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