Outcome
    Moderate Evidence
    Effectiveness 3/5

    Vitamin C for Immune Function

    Useful, cheap and safe at 200-500 mg daily. The dramatic claims made for it have not survived controlled testing.

    Overview

    Useful, cheap and safe at 200-500 mg daily. The dramatic claims made for it have not survived controlled testing.

    Verdict

    Mixed evidence

    Vitamin C supports several arms of immune function and shortens colds modestly — a sensible baseline, not a shield.

    How It Works

    Vitamin C accumulates in neutrophils and lymphocytes, supports epithelial barrier integrity, enhances neutrophil chemotaxis and phagocytosis, promotes apoptosis and clearance of spent neutrophils to limit tissue damage, and supports lymphocyte differentiation and proliferation.

    Dosing & Protocol

    Typical dose

    Recommended dose
    200-500 mg daily; higher short-term doses during infection.
    Expected timeframe
    Continuous use before exposure; no acute effect.

    Protocol

    dose
    200-500 mg daily
    form
    Ascorbic acid or buffered ascorbate
    stack
    Zinc 15-30 mg daily has complementary immune evidence
    timing
    Split doses; absorption saturates above ~400 mg per dose
    duration
    Ongoing

    Evidence

    What the studies say

    Cochrane analysis shows an 8% reduction in cold duration in adults on regular supplementation and a roughly 50% reduction in incidence among people under extreme physical stress. Intravenous high-dose vitamin C in sepsis has been studied extensively with disappointing and inconsistent results. Deficiency clearly impairs immunity; supplementation above sufficiency yields small benefits.

    Vitamin C for preventing and treating the common cold

    Score: 9/10
    2013
    systematic_review
    n=11306

    Hemila H, Chalker E

    Regular vitamin C did not reduce cold incidence in the general population but shortened duration modestly

    View source

    Vitamin C supplementation reduces the odds of developing a common cold in Republic of Korea Army recruits: randomised controlled trial

    Score: 7/10
    2022
    rct
    n=1444

    Kim TK, Lim HR, Byun JS

    The vitamin C group had a 0.80-fold lower risk of getting a common cold than did the placebo group.

    View source

    Vitamin C and immune function

    Score: 8/10
    2017
    systematic_review

    Carr AC, Maggini S

    Vitamin C contributes to immune defense by supporting various cellular functions of both the innate and adaptive immune system.

    View source

    Safety

    Caveats

    Doses above 2 g cause diarrhoea. Vitamin C is not protective against COVID-19 or influenza beyond its general modest effect on respiratory infection duration. The Cochrane review of 29 trials (11,306 participants) found no reduction in cold incidence in the general population; benefit is limited to an 8-14% shorter cold duration and to people under heavy physical stress, where incidence was roughly halved.

    Less likely to help if

    Well-nourished adults with normal intake see small effects at best.

    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.