Vitamin D and respiratory infection in adults

Proc Nutr Soc. 2012 Feb;71(1):90-7. doi: 10.1017/S0029665111003351. Epub 2011 Nov 25.


Vitamin D insufficiency is a global issue that has significant implications for health. The classical role of vitamin D in bone mineralisation is well known; vitamin D deficiency leads to rickets, osteomalacia or osteoporosis. The role of vitamin D in an immune system is less known. Vitamin D is not an actual vitamin but a secosteroid hormone produced in the skin from 7-dehydrocholesterol after exposure to sunlight UVB radiation. Nutrition and supplements are main sources of vitamin D in wintertime in northern countries as sunlight exposure is inadequate for the production. For activation vitamin D needs to be hydroxylated in liver to form 25-hydroxyvitamin D and in kidney to 1,25-dihydroxyvitamin D, the most active hormone in Ca absorption in the gut. For determination of vitamin D status serum 25-hydroxyvitamin D level, the major circulating form of the hormone is to be measured. Vitamin D regulates gene expression through binding with vitamin D receptors, which dimerises with retinoid X receptor. This complex binds to vitamin D-responsive elements inside the promoter regions of vitamin D-responsive genes. Vitamin D has a key role in innate immunity activation; the production of antimicrobial peptides (cathelicidin and defensins) following Toll-like receptor stimulation by pathogen lipopeptides is dependent on sufficient level of 25-hydroxyvitamin D. Clinically, there is evidence of the association of vitamin D insufficiency and respiratory tract infections. There is also some evidence of the prevention of infections by vitamin D supplementation. Randomised controlled trials are warranted to explore this preventive effect.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Antimicrobial Cationic Peptides / biosynthesis
  • Defensins / biosynthesis
  • Dietary Supplements
  • Gene Expression Regulation*
  • Humans
  • Immunity, Innate / genetics
  • Immunity, Innate / physiology*
  • Receptors, Calcitriol / metabolism
  • Respiratory Tract Infections / etiology*
  • Respiratory Tract Infections / prevention & control
  • Retinoid X Receptors / metabolism
  • Vitamin D / immunology*
  • Vitamin D / metabolism
  • Vitamin D / therapeutic use
  • Vitamin D Deficiency / complications*
  • Vitamin D Deficiency / drug therapy
  • Vitamin D Deficiency / immunology


  • Antimicrobial Cationic Peptides
  • Defensins
  • Receptors, Calcitriol
  • Retinoid X Receptors
  • Vitamin D
  • ropocamptide