Vitamin C for the common cold Original paper

According to this meta-analysis of randomized controlled trials, proactively supplementing with vitamin C reduced the severity of a common cold episode.

The effect of proactively supplementing with vitamin C on common cold symptoms.

The outcomes assessed were the severity of common cold symptoms and the overall duration of the common cold.

Adults and children (average ages of 9 to 44) without apparent health conditions or the common cold at baseline.

A meta-analysis of 10 randomized controlled trials was performed. Almost all of the studies had the participants take 1 gram of vitamin C daily, and the remainder either had the participants take 2 grams daily throughout the study or 2 grams daily followed by 4 grams daily for 3 days after developing the common cold. The duration of follow-up ranged from 1 week to 5 months.

Common cold severity was assessed in 1 of 3 ways: measured using a symptom severity scale, indicated by the number of days confined to the house/absent from school, or indicated by the number of days with severe symptoms.

The following results were reported for common cold severity.

Compared to placebo:

• Vitamin C reduced symptom severity by 13% (based on 5 studies; 975 participants).
• Vitamin C reduced the number of days confined to the house/absent from school by 15% (based on 3 studies; 2,736 participants).
• Vitamin C reduced the number of days of severe symptoms by 66% (based on 2 studies; 391 participants).

Vitamin C did not affect common cold duration (based on 4 studies).