Results from recent trials assessing the effect of vitamin D supplementation on the prevention of childhood acute respiratory infections (ARI) have been inconsistent. In the present study, we determined whether vitamin D supplementation prevents ARI in healthy children and repeated infections in children with previous ARI. We conducted a systematic literature search using MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials. The search included only randomised controlled clinical trials (RCT) comparing vitamin D supplementation with either placebo or no intervention in children younger than 18 years of age. We identified seven RCT and found that the summary estimates were not statistically significantly associated with a reduction in the risk of ARI (relative risk (RR) 0·79, 95 % CI 0·55, 1·13), all-cause mortality (RR 1·18, 95 % CI 0·71, 1·94), or the rate of hospital admission due to respiratory infection in healthy children (RR 0·95, 95 % CI 0·72, 1·26). However, in children previously diagnosed with asthma, vitamin D supplementation resulted in a 74 % reduction in the risk of asthma exacerbation (RR 0·26, 95 % CI 0·11, 0·59; test of heterogeneity, I
2= 0·0 %). Our findings indicate a lack of evidence supporting the routine use of vitamin D supplementation for the prevention of ARI in healthy children; however, they suggest that such supplementation may benefit children previously diagnosed with asthma. Due to the heterogeneity of the included studies and possible publication biases related to this field, these results should be interpreted with caution.