Background: Growing evidence suggests that vitamin D plays a role in the pathophysiology of childhood asthma. However, its effectiveness in reducing asthma exacerbations and improving asthma-related outcomes remains controversial. Methods: We systematically searched PubMed, Embase, and the Cochrane Library from inception to 25 February 2026. Meta-analyses of randomized controlled trials (RCTs) evaluating the effects of vitamin D supplementation on any health outcomes in children with asthma were included. Methodological quality was assessed using the AMSTAR 2 tool. The credibility of evidence was evaluated using pre-specified evidence classification criteria, and the certainty of evidence was graded using the GRADE approach. Results: A total of 14 systematic reviews were included, of which one was rated as high quality, six as low quality, and seven as critically low quality according to AMSTAR 2. Vitamin D supplementation significantly increased serum 25-hydroxyvitamin D levels in children with asthma (MD = 10.68 ng/mL; 95% CI, 6.30 to 15.05; n = 8 RCTs), although the evidence was of low credibility (class IV) and very low certainty. No significant improvements were observed in Childhood Asthma Control Test scores (MD = 0.15; 95% CI, −0.43 to 0.74; n = 3 RCTs; class V; moderate), overall asthma exacerbations (RR = 0.84; 95% CI, 0.65 to 1.08; n = 11 RCTs; class V; low), or lung function as measured by percent predicted forced expiratory volume in 1 second (SMD = 0.49; 95% CI, −0.05 to 1.04; n = 5 RCTs; class V; moderate). One meta-analysis suggested a possible reduction in asthma recurrence (RR = 0.53; 95% CI, 0.35 to 0.79; n = 6 RCTs; class IV; moderate). Conclusions: This umbrella review found no convincing evidence that vitamin D supplementation improves asthma control, reduces exacerbations, or enhances lung function in children with asthma, despite its effect on increasing serum 25-hydroxyvitamin D levels and a possible benefit for asthma recurrence. However, these findings should be interpreted with caution, considering that the available evidence was limited by generally low methodological quality, substantial overlap among meta-analyses, and incomplete reporting of clinically relevant modifiers.
Liu et al. (Thu,) studied this question.