Vitamin C
While many consumers still think of vitamin C when they think about an immune supplement, there have been some questions raised about the efficacy of the vitamin to reduce the incidence of the common cold.
A review of 30 studies published in The Cochrane Library (2013, doi: 10.1002/14651858.CD000980.pub4) concluding that daily doses of at least 200 milligrams did little to reduce the length or severity of a cold. However, the review also found that daily supplements of vitamin C may reduce the risk of developing common cold for marathon runners by 50% at a dose of 0.2 grams per day.
Select analysis further revealed that vitamin C supplements did reduce the duration of common colds in adult and children by 8% and 14%, respectively. In addition, a dose of 1 to 2 grams per day reduced the duration by 18% for children.
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