Condition
    Moderate Evidence
    Effectiveness 3/5

    Vitamin D for Recurring Infections

    Vitamin D has the strongest supplement evidence for infection prevention — a 25-trial individual-patient meta-analysis found it reduced respiratory infections, with benefit roughly doubling in people who were deficient.

    Overview

    Vitamin D has the strongest supplement evidence for infection prevention — a 25-trial individual-patient meta-analysis found it reduced respiratory infections, with benefit roughly doubling in people who were deficient.

    Verdict

    Mixed evidence

    How It Works

    Vitamin D receptors sit on immune cells, where the hormone supports antimicrobial peptide production and calibrates inflammatory responses. Deficiency measurably impairs front-line immune defence.

    Dosing & Protocol

    Typical dose

    Recommended dose
    1,000-2,000 IU daily; test 25-OH vitamin D to guide dosing
    Expected timeframe
    8-12 weeks to replete; assess over a season

    Protocol

    form
    Vitamin D3 (cholecalciferol) taken daily - this matters, because the effect is confined to daily or weekly dosing
    duration
    At least 6-12 months, counting infection episodes
    co factor
    Take with the largest meal. Evidence is mixed but has a clear pattern: the individual participant data meta-analysis of acute respiratory infection trials found daily or weekly vitamin D reduced infection risk, with the benefit concentrated in people who were profoundly deficient at baseline (below 25 nmol/L), and no benefit from monthly bolus dosing or in replete people.
    titration
    Target 75-125 nmol/L; avoid large intermittent bolus doses, which were ineffective in the trials
    starting dose
    1000-2000 IU (25-50 mcg) vitamin D3 daily with a fat-containing meal, after checking 25-hydroxyvitamin D

    Evidence

    What the studies say

    The Martineau individual-patient meta-analysis across 25 randomised trials (n≈11,000) found vitamin D supplementation reduced acute respiratory infections overall, with the strongest protection in people starting deficient (25-OH-D below 25 nmol/L) and with daily dosing rather than boluses. It is a deficiency-correction effect. The other checkable causes of recurrent infections — iron deficiency, diabetes, sleep deprivation — have their own evidence and should be tested in parallel.

    Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data

    Score: 9/10
    2017
    meta_analysis
    n=11321

    Martineau AR, Jolliffe DA, Hooper RL +3 more

    Vitamin D reduced acute respiratory infection risk overall, with the largest benefit in deficient participants

    View source

    Safety

    Caveats

    Upper safe limit 4,000 IU/day without monitoring. Benefit concentrates in the deficient — megadoses in replete people add nothing.

    Less likely to help if

    People with normal vitamin D levels, and anyone using monthly bolus dosing rather than daily.

    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.