INTERPRETATION Results indicate that vitamin D has a protective effect against RTI , and dosing once-daily seems most effective .
BACKGROUND Low levels of 25-OH vitamin D are associated with  respiratory tract infection ( RTI ) .
However , results from r and omized controlled trials are inconclusive .
Therefore , we performed a systematic review and meta- analysis to assess the preventive effect of vitamin D supplementation on RTI .
Vitamin D accelerates resolution of inflammatory responses during tuberculosis treatment
Calcidiol , the major circulating metabolite of vitamin D , supports induction of pleiotropic antimicrobial responses in vitro . Vitamin D supplementation elevates circulating calcidiol concentrations , and thus has a potential role in the prevention and treatment of infection . The immunomodulatory effects of administering vitamin D to humans with an infectious disease have not previously been reported . To characterize these effects , we conducted a detailed longitudinal study of circulating and antigen-stimulated immune responses in ninety-five patients receiving antimicrobial therapy for pulmonary tuberculosis who were r and omized to receive adjunctive high-dose vitamin D or placebo in a clinical trial , and who fulfilled criteria for per- protocol analysis . Vitamin D supplementation accelerated sputum smear conversion and enhanced treatment-induced resolution of lymphopaenia , monocytosis , hypercytokinaemia , and hyperchemokinaemia . Administration of vitamin D also suppressed antigen-stimulated proinflammatory cytokine responses , but attenuated the suppressive effect of antimicrobial therapy on antigen-stimulated secretion of IL-4 , CC chemokine lig and 5 , and IFN-α . We demonstrate a previously unappreciated role for vitamin D supplementation in accelerating resolution of inflammatory responses during tuberculosis treatment . Our findings suggest a potential role for adjunctive vitamin D supplementation in the treatment of pulmonary infections to accelerate resolution of inflammatory responses associated with increased risk of mortality
INTERPRETATION Results indicate that vitamin D has a protective effect against RTI , and dosing once-daily seems most effective .
BACKGROUND Low levels of 25-OH vitamin D are associated with  respiratory tract infection ( RTI ) .
However , results from r and omized controlled trials are inconclusive .
Therefore , we performed a systematic review and meta- analysis to assess the preventive effect of vitamin D supplementation on RTI .