Vitamin D supplementation in childhood asthma: a systematic review and meta-analysis of randomised controlled trials

BACKGROUND: There is conflicting evidence for vitamin D supplementation in childhood asthma. We aimed to systematically synthesise the evidence on the efficacy and safety of vitamin D supplementation in childhood asthma. METHODS: We searched electronic databases (Medline, Embase and Web of Science) and a register (CENTRAL) for randomised controlled trials (RCTs) published until 30 September 2021. RCTs enrolling asthmatic children (1–18 years old) and comparing vitamin D against placebo/routine care were included if they met at least one of the endpoints of interest (asthma attacks, emergency visits or hospitalisation). We used the Risk of Bias 2 tool for risk of bias assessment. Random-effects meta-analysis with RevMan 5.3 software was performed. The Grading of Recommendations Assessment, Development and Evaluation approach was used to assess the level of certainty of the evidence. RESULTS: 18 RCTs (1579 participants) were included. The pooled meta-analysis did not find a significant effect of vitamin D supplementation on asthma attacks requiring rescue systemic corticosteroids (six studies with 445 participants; risk ratio (RR) 1.13, 95% CI 0.86–1.48; I(2)=0%) (moderate-certainty evidence). In addition, there was no significant difference in the proportion of children with asthma attacks of any severity (11 trials with 1132 participants; RR 0.84, 95% CI 0.65–1.09; I(2)=58%) (very low-certainty evidence). Vitamin D does not reduce the need for emergency visits (three studies with 361 participants; RR 0.97, 95% CI 0.89–1.07; I(2)=0%) and hospitalisation (RR: 1.38, 95% CI 0.52–3.66; I(2)=0%) (low-certainty evidence). CONCLUSION: Very low- to moderate-certainty evidence suggests that vitamin D supplementation might not have any protective effect in childhood asthma.