The Role of Vitamin D in Severity and Control of Asthma in Children and Adolescents: A Systematic Review and Meta‐Analysis

CONTEXT: Vitamin D may modulate the inflammatory processes involved in asthma. OBJECTIVE: To synthesize evidence on the association between serum 25-hydroxyvitamin D levels and asthma control, severity, pulmonary function, and inflammatory markers in children and adolescents. DATA SOURCES: MEDLINE PubMed, BIREME, EBSCOhost, Scopus, Web of Science, EMBASE, Cochrane Library, and ProQuest until May 2025. STUDY SELECTION: Eligible studies enrolled participants aged 2-18 years with clinically diagnosed asthma and evaluated serum vitamin D levels in relation to asthma severity and/or control and pulmonary function parameters or type 2 inflammatory biomarkers. We included observational and randomized studies. DATA EXTRACTION: The risk of bias for studies was assessed. Random-effects models estimated pooled outcomes. The heterogeneity was assessed using Cochran's Q and the I² statistic. RESULTS: Forty-one studies (7780 participants) were included; 25 contributed to meta-analyses. Children with asthma had significantly lower serum 25(OH)D levels than healthy controls (mean difference -4.89 ng/mL; 95% CI -7.38 to -2.40; p < 0.001). Severe asthma was associated with lower vitamin D compared with mild disease (-4.21 ng/mL; 95% CI -6.43 to -1.98; p = 0.0002). No significant difference was observed between controlled and uncontrolled asthma. Correlations with pulmonary function were weak and non-significant (FEV₁ r = 0.18; p = 0.08). Vitamin D showed a moderate inverse association with total IgE (r = -0.37; p = 0.02), but not with eosinophil counts or IL-10. Heterogeneity was high across analyses. CONCLUSIONS: Children with asthma exhibit lower serum vitamin D levels compared with healthy peers, and these levels are inversely associated with asthma severity and total IgE. No consistent associations were observed with pulmonary function or asthma control. Further research is needed to determine whether correcting vitamin D deficiency can improve clinical and immunologic outcomes in pediatric asthma.