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Evidence-Based Supplement Research
Evidence-Based Supplement Research
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Vitamin C and Improved Lung Function

Research synthesisLow evidenceMixed effect size4 studies · 2 beneficial · 2 neutral · 0 harmful

Across 4 studies, 2 reported beneficial effects (one moderate-sized and statistically significant), while 2 found neutral effects. The predominant effect direction is mixed (beneficial and neutral), with effect sizes ranging from small to moderate. The most-studied population is clinical (pregnant smokers and individuals with asthma or COPD), and the evidence from the highest-quality study (RCT, n=137) showed a moderate beneficial effect at 500 mg/day on lung function, though this finding comes from a single study and was not replicated in larger meta-analyses.

  • Effective dose range: 500 mg/day (based on the single beneficial RCT); other studies used variable or unreported doses
  • Studied populations: pregnant smokers and their children at age 5; adults with asthma or exercise-induced bronchoconstriction; patients with COPD

Caveats: Evidence base is small (only 4 studies) — conclusions should be considered preliminary. Many of the included studies did not reach statistical significance — effect may be smaller than the predominant direction suggests. Available evidence is mixed: the only statistically significant finding comes from a single RCT in a specific population (children of pregnant smokers), while meta-analyses in asthma and COPD found no significant benefit.

Generated Jun 11, 2026
Doses used in studies
  • mg/day: 500 (median 500, IQR 500–500) — 1 study
Safety in these studies
4 of 4 papers
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