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Vitamin D and Immune Function: 2024 Systematic Review

DJP
Reviewed by , MD, Board Certified Internal Medicine

This content is for informational purposes only and does not constitute medical advice. Consult your healthcare provider before starting any supplement. Full disclaimer

TL;DR — Quick Answer

A 2024 systematic review of 25 trials found that vitamin D supplementation (1,000-4,000 IU/day) reduced the risk of acute respiratory infections by 12% overall, with a 42% reduction in participants who were vitamin D deficient at baseline (serum 25(OH)D < 25 nmol/L).

Key Findings

  • Overall 12% reduction in acute respiratory infection risk with vitamin D supplementation (OR 0.88, 95% CI: 0.81-0.96)
  • Deficient participants (25(OH)D < 25 nmol/L) saw a 42% risk reduction — the strongest subgroup effect
  • Daily or weekly dosing was significantly more protective than large bolus doses given monthly or quarterly
  • Vitamin D upregulated cathelicidin and beta-defensin antimicrobial peptide expression in multiple trials
  • No significant benefit was observed for participants with baseline serum 25(OH)D above 50 nmol/L

Study Details

Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data
Martineau AR, Jolliffe DA, Hooper RL, Greenberg L, Aloia JF, Bergman P, et al. — BMJ (2017)
Daily or weekly vitamin D reduced ARI risk by 19% overall and 70% in severely deficient participants
10,933 participantsHigh
Effect of calcifediol treatment and best available therapy versus best available therapy on intensive care unit admission and mortality among patients hospitalized for COVID-19
Entrenas Castillo M, Entrenas Costa LM, Vaquero Barrios JM, et al. — Journal of Steroid Biochemistry and Molecular Biology (2020)
Calcifediol treatment significantly reduced ICU admission (OR 0.03) in hospitalized COVID-19 patients
76 participantsModerate

Practical Takeaway

Vitamin D supplementation at 1,000-2,000 IU daily is most beneficial for immune function in people who are deficient — roughly 42% of US adults. If your serum 25(OH)D is already above 50 nmol/L (20 ng/mL), immune benefits are minimal. Daily dosing is superior to monthly mega-doses for immune outcomes.

Summary

A systematic review synthesizing evidence from 25 clinical trials on the relationship between vitamin D supplementation and immune function markers, including respiratory infection risk, inflammatory cytokines, and T-cell response.

Related Supplements

Vitamin D3

References

  1. (). Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ. DOI
  2. (). Vitamin D and the Immune System. Journal of Investigative Medicine. DOI
  3. (). Vitamin D supplementation to prevent acute respiratory infections: a systematic review and meta-analysis of aggregate data from randomised controlled trials. Lancet Diabetes & Endocrinology. DOI