Vitamin C supplementation (ascorbic acid)
Oral vitamin C has been tested in placebo-controlled trials for preventing and treating the common cold; pooled evidence shows essentially no incidence reduction in the general community, clearer relative reductions in some high-strain athlete and subarctic-exercise cohorts, modest duration effects in children with regular use, and no consistent benefit when therapy starts at symptom onset.
Scope
Vitamin C supplementation here means oral ascorbic acid (typically ≥0.2 g/day in included placebo-controlled trials) studied for common cold incidence, duration, or severity—not intravenous vitamin C in sepsis/oncology protocols, skin topical formulations, or multivitamin matrices where vitamin C cannot be isolated statistically.
Evidence anchors (PubMed)
- Cochrane review (prevention + treatment): Hemilä & Chalker 2013 (PMID 23440782;
hemila-2013-vitamin-c-common-cold-cochrane) — pooled 29 trial comparisons (n = 11,306) on cold incidence during regular supplementation; community pooled RR 0.97 (95% CI 0.94–1.00) versus athlete / skier / subarctic-exercise pooled RR 0.48 (95% CI 0.35–0.64). Therapeutic vitamin C at onset (7 comparisons) showed no consistent effect on duration or severity.
Distinct protocols (do not merge)
- Zinc supplementation (lozenges / salts) (
zinc-supplementation) — different pharmacology and Cochrane effect profile for treatment duration; occasional consumer combination tablets are not evidence-sums of single agents. - Marine omega-3 (
marine-omega-3-supplementation) — EPA/DHA lipid axis. - Magnesium supplementation (
magnesium-supplementation) — mineral sleep trials.
Evidence hygiene
Community null on incidence does not erase narrow-population signals—always read exposure context (marathon training, winter field exercises) before personalising doses.