Despite the popular belief that vitamin C can cure the common cold, the scientific evidence for this is conflicting. A few studies have suggested that taking vitamin C supplements when you are exposed to a cold virus or when you first have symptoms can shorten a cold or even prevent one. Other research has shown that vitamin C supplementation has no impact on a cold's severity or length, but it can significantly reduce how often a person catches a cold.

Vitamin C may only be useful in case of a cold if you have low levels of this nutrient to begin with. 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 non-absorption or urination.

Sasazuki S, Sasaki S, Tsubono Y, Okubo S, Hayashi M, Tsugane S. Effect of vitamin C on common cold: randomized controlled trial. Eur J Clin Nutr. 2005 Aug 24.

Douglas RM, Hemila H. Vitamin C for preventing and treating the common cold. PLoS Med. 2005 Jun;2(6):e168; quiz e217. Epub 2005 Jun 28.

Hemila H. Vitamin C supplementation and respiratory infections: a systematic review. Mil Med. 2004 Nov;169(11):920-5.

Douglas RM, Hemila H, D'Souza R, Chalker EB, Treacy B. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2004 Oct 18;(4):CD000980.

Simasek M, Blandino DA. Treatment of the common cold. Am Fam Physician. 2007:75(4):515-520.