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 .
Effects of vitamin D supplementation to children diagnosed with pneumonia in Kabul: a randomised controlled trial.
OBJECTIVES To determine whether ( i ) supplementation of oral 100,000 iu of vitamin D(3 ) ( cholecalciferol ) along with antibiotics will reduce the duration of illness in children with pneumonia ; ( ii ) supplementation will reduce the risk of repeat episodes . METHODS Double-blind individually r and omised placebo-controlled trial in an inner-city hospital in Kabul , of 453 children aged 1 - 36 months , diagnosed with non-severe or severe pneumonia at the outpatient clinic . Children with rickets , other concurrent severe diseases , very severe pneumonia or wheeze , were excluded . Children were given vitamin D(3 ) or placebo drops additional to routine pneumonia treatment . RESULTS Two hundred and twenty-four children received vitamin D(3 ; ) and 229 received placebo .  There was no significant difference in the mean number of days to recovery between the vitamin D(3 ) ( 4.74 days ; SD 2.22 ) and placebo arms ( 4.98 days ; SD 2.89 ; P = 0.17 ) . The risk of a repeat episode of pneumonia within 90 days of supplementation was lower in the intervention ( 92/204 ; 45 % ) than the placebo group [ 122/211 ; ( 58 % ; relative risk 0.78 ; 95 % CI 0.64 , 0.94 ; P = 0.01 ] . Children in the vitamin D(3 ) group survived longer without experiencing a repeat episode ( 72 days vs. 59 days ; HR 0.71 ; 95 % CI 0.53 - 0.95 ; P = 0.02 ) . CONCLUSION A single high-dose oral vitamin D(3 ) supplementation to young children along with antibiotic treatment for pneumonia could reduce the occurrence of repeat episodes of pneumonia
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 .