Outcome
    Moderate Evidence

    Vitamin C for Respiratory Tract Protection

    Regular vitamin C slightly shortens colds but does not prevent them in the general population.

    Overview

    Regular vitamin C slightly shortens colds but does not prevent them in the general population.

    Verdict

    Insufficient evidence

    How It Works

    Supports neutrophil function and epithelial barrier integrity.

    Dosing & Protocol

    Typical dose

    Recommended dose
    200mg/day regularly; not useful started at onset
    Expected timeframe
    Ongoing

    Protocol

    form
    Ascorbic acid, or buffered ascorbate if stomach upset occurs
    duration
    Regular use across a season in the prevention trials
    co factor
    Evidence is insufficient for broad respiratory protection. The Cochrane review found regular vitamin C at 200 mg/day or more does not reduce cold incidence in the general population, though it shortens duration by about 8% in adults, and halves incidence in people under extreme physical stress such as marathon runners and soldiers in subarctic conditions. For pneumonia the evidence is limited to a few old trials in specific populations. In critical illness, high-dose intravenous vitamin C for sepsis and ARDS was tested in the LOVIT and VICTAS trials, with LOVIT finding a higher risk of death or persistent organ dysfunction.
    titration
    Not applicable; the tolerable upper intake level is 2,000 mg/day for adults
    starting dose
    Not established for this outcome. Regular-use trials used 200 mg/day or more; therapeutic trials used 1-8 g/day at symptom onset

    Evidence

    What the studies say

    Cochrane found no reduction in cold incidence with routine supplementation, a small reduction in duration, and a halving of incidence specifically in marathon runners, soldiers and subarctic troops.

    No studies are yet linked to both Vitamin C and Respiratory Tract Protection.

    Safety

    Caveats

    High doses cause GI upset and raise kidney stone risk in susceptible people.

    Less likely to help if

    Everyone outside extreme-exertion groups, where only cold incidence was affected.

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    Individual results may vary. The statements on this website have not been evaluated by the Food and Drug Administration. Products and information are not intended to diagnose, treat, cure, or prevent any disease.