Full-text evidence summary

InfluenzaHow does vitamin D work?

 Vitamin D prevents influenza and pneumonia by strengthening the body’s innate immune system. 

The primary epithelial cells generate 1,25-hydroxyvitamin D, which then influences the expression of vitamin D-driven genes that play a major role in host defense through inducing production of cathelicidin and defensins1.  These compounds have antimicrobial and antiendotoxin properties2.  

For pneumonia, the roles of vitamin D include reducing the cytokine storm by shifting production from T-helper 1 (Th1) to Th2 cytokines, which generate less inflammation3 and fighting the bacterial pneumonia through induction of cathelicidin and defensins as reviewed in Grant and Giovannucci4.  

The vitamin D-antimicrobial peptide pathway and its role in protection against infection was recently discussed by Gombart5.

Page last edited: 17 May 2011


  1. Hansdottir, S. Monick, M. M. Hinde, S. L. Lovan, N. Look, D. C. Hunninghake, G. W. Respiratory epithelial cells convert inactive vitamin D to its active form: potential effects on host defense. J Immunol. 2008 Nov 15; 181 (10): 7090-9.
  2. Mookherjee, N. Rehaume, L. M. Hancock, R. E. Cathelicidins and functional analogues as antisepsis molecules. Expert Opin Ther Targets. 2007 Aug; 11 (8): 993-1004.
  3. Ardizzone, S. Cassinotti, A. Trabattoni, D. Manzionna, G. Rainone, V. Bevilacqua, M. Massari, A. Manes, G. Maconi, G. Clerici, M. Bianchi Porro, G. Immunomodulatory effects of 1,25-dihydroxyvitamin D3 on TH1/TH2 cytokines in inflammatory bowel disease: an in vitro study. Int J Immunopathol Pharmacol. 2009 Jan-Mar; 22 (1): 63-71.
  4. Grant, W. B. Giovannucci, E. The possible roles of solar ultraviolet-B radiation and vitamin D in reducing case-fatality rates from the 1918-1919 influenza pandemic in the United States. Dermato-Endocrinology. 2009; 1 (4): 215-219.
  5. Gombart, A. F. The vitamin D-antimicrobial peptide pathway and its role in protection against infection. Future Microbiol. 2009 Nov; 41151-65.