Vitamin D and asthma in children: A systematic review and meta-analysis of observational studies.

There is growing literature suggesting a link between Vitamin D deficiency and asthma in children, but systematic reviews are lacking. The aim of this study is to evaluate the prevalence of Vitamin D deficiency in asthmatic children and to assess the correlations of Vitamin D levels with asthma incidence, asthma control, and lung functions. PubMed, EMBASE, and Cochrane Library were searched for observational studies on asthma and Vitamin D. Two authors independently extracted data. Meta-analysis was performed using the Review Manager Software. A total of 23 (11 case-control, 5 cohort, and 7 cross-sectional) studies enrolling 13,160 participants were included in the review. Overall, Vitamin D deficiency and insufficiency were prevalent in 28.5% and 26.7% children with asthma, respectively. The mean 25-hydroxyvitamin D (25(OH)D) levels (10 studies) were significantly lower in asthmatic children as compared to nonasthmatic children with a mean difference of -9.41 (95% confidence interval [CI] -16.57, -2.25). The odds ratio of Vitamin D deficiency (eight case-control studies) was significantly higher among asthmatic children as compared to nonasthmatic children (odds ratio 3.41; 95% CI 2.04, 5.69). Correlations between Vitamin D levels and incidence of asthma, lung functions, and control of asthma had mixed results. To conclude, asthmatic children had lower 25(OH)D levels as compared to nonasthmatic children, but the correlations between 25(OH)D and asthma incidence, asthma control, and lung functions were varied. Well-designed randomized controlled trials are required to determine if children with asthma can benefit from Vitamin D supplementation.