Outcome
    Moderate Evidence
    Effectiveness 2/5

    Vitamin C for Flu Prevention

    Regular vitamin C does not prevent respiratory infections in the general population but modestly shortens duration and severity; it does show prevention benefit under heavy physical stress.

    Overview

    Regular vitamin C does not prevent respiratory infections in the general population but modestly shortens duration and severity; it does show prevention benefit under heavy physical stress.

    Verdict

    Mixed evidence

    Duration-reducer, not preventer — except for athletes in heavy training.

    How It Works

    Vitamin C concentrates in immune cells, supports neutrophil function and epithelial barrier integrity, and is consumed rapidly during infection.

    Dosing & Protocol

    Typical dose

    Recommended dose
    500–1,000 mg/day during high-exposure periods
    Expected timeframe
    Continuous through season; duration benefit per illness.

    Protocol

    dose
    500–1,000 mg
    notes
    Start before exposure — post-onset megadosing is unproven.
    timing
    daily during high-risk periods
    duration
    ongoing through season

    Evidence

    What the studies say

    Cochrane review: regular supplementation (≥200 mg/day) showed no incidence reduction in the general population, ~8% shorter cold duration in adults, and ~50% incidence reduction in people under heavy physical stress (marathoners, soldiers).

    No studies are yet linked to both Vitamin C and Flu Prevention.

    Safety

    Caveats

    High doses cause GI upset and loose stools; kidney stone risk at chronic high doses in susceptible people.

    Less likely to help if

    General population expecting prevention; benefit is duration and severity.

    Medical Disclaimer

    The information provided on this website is for educational and informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before starting any supplement regimen.

    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.