To evaluate the efficacy and safety of vitamin D supplementation as an adjunctive treatment for asthma and to assess the credibility of the existing evidence.
Key Findings:
Twenty-one systematic reviews and meta-analyses were included.
Vitamin D supplementation was associated with a lower risk of asthma exacerbations.
Effects on asthma control, lung function, and inflammatory outcomes were limited or inconsistent.
No significant increase in adverse events was observed.
The certainty of evidence varied across outcomes, with many findings supported by low or very low certainty evidence.
Interpretation:
Vitamin D supplementation may reduce asthma exacerbations and appears to be safe as an adjunctive treatment, but current evidence does not consistently support improvements in daily symptom control, lung function, or inflammatory outcomes.
Limitations:
Heterogeneity among studies.
Evidence uncertainty.
Substantial overlap among primary studies.
Conclusion:
Future studies should identify patients most likely to benefit and clarify optimal dose, duration, and biomarker-guided supplementation strategies.
