Large doses of vitamin C may help reduce the duration of a cold, but they do not appear to protect against one in the first place, even after exposure to a cold virus.
Vitamin C may only be useful in case of a cold if you have low levels of this nutrient to begin with. For example, the vitamin may be useful for preventing a cold if you live in very low temperature environments, or you are routinely involved in vigorous exercise such as marathon running.
The likelihood of success may be very individual -- some people improve, while others do not.
People with kidney disease should avoid vitamin C supplements. Most experts advise that you meet your daily vitamin and mineral requirements by eating a balanced diet. Taking more than 500 mg of vitamin C at any one time provides no advantage. More than that amount is simply lost through nonabsorption or urination.
Colds and vitamin C
Douglas RM, Hemilä H, Chalker E, Treacy B. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2007 Jul 18;(3):CD000980.
Kilgore D. Common respiratory diseases. Prim Care. 2010;37(2):297-324.
Updated by: Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.
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