e200921c_sity_of_Michigan_Health_System__Why
[Supplement] 3 Stars Vitamin C 1 to 4 grams daily [Why] 
Studies have shown that taking vitamin C may make your cold shorter and less severe. A review of 21 controlled trials using 1 to 8 grams of vitamin C per day found that “in each of the twenty-one studies, vitamin C reduced the duration of episodes and the severity of the symptoms of the common cold by an average of 23%.”10 The optimum amount of vitamin C to take for cold treatment remains in debate but may be as high as 1 to 3 grams per day, considerably more than the 120 to 200 mg per day that has been suggested as optimal intake for healthy adults. A review of 23 controlled trials found that vitamin C supplementation produces a greater benefit for children than for adults.11 The same review found that a daily amount of 2 grams or more was superior to a daily amount of 1 gram at reducing the duration of cold symptoms.
Common Cold/Sore Throat (Holistic) | University of Michigan Health System
Why