There was no significant effect for asthma symptom scores and lung function .
Conclusions and Relevance R and omized controlled trials provide some low- quality evidence to support vitamin D supplementation for the reduction of asthma exacerbations .
Importance There is growing evidence that vitamin D plays a role in the pathogenesis of asthma but it is unclear whether supplementation during childhood may improve asthma outcomes .
Objectives The objective of this systematic review and meta- analysis was to evaluate the efficacy and safety of vitamin D supplementation as a treatment or adjunct treatment for asthma .
Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren.
BACKGROUND To our knowledge , no rigorously design ed clinical trials have evaluated the relation between vitamin D and physician-diagnosed seasonal influenza . OBJECTIVE We investigated the effect of vitamin D supplements on the incidence of  seasonal influenza A in schoolchildren . DESIGN From December 2008 through March 2009 , we conducted a r and omized , double-blind , placebo-controlled trial comparing vitamin D(3 ) supplements ( 1200 IU/d ) with placebo  in schoolchildren . The primary outcome was the incidence of influenza A , diagnosed with influenza antigen testing with a nasopharyngeal swab specimen . RESULTS Influenza A occurred in 18 of 167 ( 10.8 % ) children in the vitamin D(3 ) group compared with 31 of 167 ( 18.6 % ) children in the  placebo  group [ relative risk ( RR ) , 0.58 ; 95 % CI : 0.34 , 0.99 ; P = 0.04 ] . The reduction in influenza A was more prominent in children who had not been taking other vitamin D supplements ( RR : 0.36 ; 95 % CI : 0.17 , 0.79 ; P = 0.006 ) and who started nursery school after age 3 y ( RR : 0.36 ; 95 % CI : 0.17 , 0.78 ; P = 0.005 ) . In children with a previous diagnosis of asthma , asthma attacks as a secondary outcome occurred in 2 children receiving vitamin D(3 ) compared with 12 children receiving placebo ( RR : 0.17 ; 95 % CI : 0.04 , 0.73 ; P = 0.006 ) . CONCLUSION This study suggests that vitamin D(3 ) supplementation during the winter may reduce the incidence of influenza A , especially in specific subgroups of schoolchildren . This trial was registered at https://center.umin.ac.jp as UMIN000001373
There was no significant effect for asthma symptom scores and lung function .
Conclusions and Relevance R and omized controlled trials provide some low- quality evidence to support vitamin D supplementation for the reduction of asthma exacerbations .
Importance There is growing evidence that vitamin D plays a role in the pathogenesis of asthma but it is unclear whether supplementation during childhood may improve asthma outcomes .
Objectives The objective of this systematic review and meta- analysis was to evaluate the efficacy and safety of vitamin D supplementation as a treatment or adjunct treatment for asthma .