Vitamin C supplementation and common cold symptoms: factors affecting the magnitude of the benefit.
Level 1 - systematic review of randomized trials
Review and analysis of 23 placebo-controlled trials.
PubMed 10340298 · doi:10.1054/mehy.1997.0639
What was done
The author analyzed 23 placebo-controlled trials evaluating regular daily vitamin C supplementation (≥1 g/day) to identify factors explaining variation in reported benefits on common cold duration and severity.
What was found
Vitamin C supplementation was associated with greater average reductions in cold duration for children than for adults, with higher doses (≥2 g/day) yielding larger reductions than 1 g/day. In five trials of adults receiving 1 g/day, the median decrease in cold duration was 6%, compared to a 26% median decrease across two trials of children receiving 2 g/day. Total participant count and variance estimates were not reported in the abstract.
Why it matters
This review suggests that dosage and age differences may account for the inconsistent results across previous clinical trials evaluating vitamin C for common cold symptoms.
Limits
The key subgroup comparisons rely on very small numbers of trials (only two trials in the high-dose pediatric group). Total participant numbers, search methodology, and study quality assessments are absent from the abstract, and the included studies assessed continuous daily prophylaxis rather than acute treatment initiated at symptom onset.
Cited by
- partial In a meta-analysis of 23 clinical studies involving over 6,000 participants, vitamin C supplementation of at least 2 grams daily reduced cold duration in adults by 21% and in children by 26%, compared to 6% in adults and 17% in children with 1 gram daily.