Large doses of vitamin C may help reduce how long a cold lasts, but they do not appear to protect against getting a cold. This is true even after being exposed to the virus that causes colds.
Taking a vitamin C supplement may help treat a cold only if your body currently has low levels of this vitamin. For example, people who live in cold climates may have low levels of vitamin C, so taking a vitamin C supplement may help keep this group of people from getting colds. This is also true for people who routinely do vigorous exercise, such as running marathons.
The likelihood of success may vary from person to person. Some people improve, while others do not. People with kidney disease should not take vitamin C supplements.
Taking more than 500 milligrams (mg) of vitamin C at any one time is not helpful. More than that amount is simply lost by our body not absorbing it all or through urination.
Most experts advise that you should eat a balanced diet to get your daily vitamin and mineral requirements.
Colds and vitamin C
Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013;1:CD000980. DOI: 10.1002/14651858.CD000980.pub4.
Livingston C, Cozzens J, Hamilton A. Treatments for symptoms of the common cold. Am Fam Phys. 2013;88(3):864C-864D.
Update Date 5/5/2014
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, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.