Available evidence from this systematic review suggests that high dose vitamin D may prevent  asthma exacerbation .
CONTEXT Observational studies have suggested a relationship between vitamin D status and asthma-related respiratory outcomes .
The benefit of vitamin D supplementation for pulmonary function , symptoms and exacerbations is not well established .
OBJECTIVE To systematic ally review paediatric clinical trials investigating the role of vitamin D on asthma-related respiratory outcomes .
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
Available evidence from this systematic review suggests that high dose vitamin D may prevent  asthma exacerbation .
CONTEXT Observational studies have suggested a relationship between vitamin D status and asthma-related respiratory outcomes .
The benefit of vitamin D supplementation for pulmonary function , symptoms and exacerbations is not well established .
OBJECTIVE To systematic ally review paediatric clinical trials investigating the role of vitamin D on asthma-related respiratory outcomes .