Vitamin C may alleviate exercise-induced bronchoconstriction: a meta-analysis.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of placebo-controlled trials
PubMed 23794586 · doi:10.1136/bmjopen-2012-002416
What was done
Systematic review and meta-analysis of MEDLINE and Scopus searching for placebo-controlled trials evaluating vitamin C administration for exercise-induced bronchoconstriction (EIB). Primary outcomes were the arithmetic difference and relative effect in post-exercise forced expiratory volume in 1 s (FEV1) decline between vitamin C and placebo periods, pooled via the inverse variance method and linear modeling. The secondary outcome was the difference in the proportion of participants experiencing EIB.
What was found
Three placebo-controlled trials with a total of 40 participants were identified. Pre-exercise vitamin C administration resulted in a pooled reduction of 8.4 percentage points (95% CI 4.6 to 12) in post-exercise FEV1 decline compared to placebo, corresponding to a pooled relative reduction of 48% (95% CI 33% to 64%). One trial showed vitamin C reduced the proportion of participants experiencing EIB by 50 percentage points (95% CI 23 to 68).
Why it matters
This meta-analysis indicates that vitamin C may substantially reduce bronchoconstriction after exertion, presenting a safe, accessible, and low-cost intervention for individuals with exercise-associated respiratory symptoms.
Limits
The evidence base is very small, encompassing only 40 participants across three studies. One included trial required data imputation for the primary meta-analysis. The abstract does not specify vitamin C dosing regimens, administration timing, participant demographics, or long-term safety.
Cited by
- supports A meta-analysis of three placebo-controlled studies found that 0.5 to 2 grams of vitamin C taken immediately before exercise for two weeks reduced the exercise-induced FEV1 decline by more than 8%.