Vitamin D Status and Asthma Severity in School-Aged Children: A Case Control Study

Abstract

Background: Vitamin D has been increasingly implicated in immune modulation and airway inflammation in asthma. South Asian children, despite abundant ambient sunshine, demonstrate widespread vitamin D deficiency due to cultural, dietary and environmental factors. Local evidence linking 25-hydroxyvitamin D [25(OH)D] status to asthma severity and control in Pakistani children remains limited. This study compared serum 25(OH)D concentrations between asthmatic and non-asthmatic children and assessed the relationship between vitamin D status, asthma severity and asthma control. Methods: A single-centre, prospective, hospital-based, age- and sex-matched case-control study was conducted between January 2024 and December 2025. A total of 150 children aged 5 to 15 years were enrolled: 75 cases with physician-diagnosed asthma (GINA-classified) and 75 non-asthmatic controls. Serum 25(OH)D was measured by electrochemiluminescence immunoassay. Asthma severity was classified by GINA criteria; control was assessed using the Childhood Asthma Control Test (cACT). Results: Mean serum 25(OH)D was significantly lower in cases than controls (16.4 ± 7.2 vs 24.6 ± 8.4 ng/mL; p < 0.001). Vitamin D deficiency (<20 ng/mL) was present in 56.0% of cases versus 28.0% of controls (p < 0.001). Among cases, mean 25(OH)D decreased progressively with worsening severity (mild 20.4 ± 6.8, moderate 15.2 ± 6.0, severe 11.4 ± 5.2 ng/mL; p for trend <0.001). Serum 25(OH)D correlated positively with cACT score (r = 0.524, p < 0.001) and FEV₁% predicted (r = 0.458, p < 0.001), and negatively with ICS dose (r = –0.392, p = 0.001) and exacerbations in the previous year (r = –0.486, p < 0.001). On multivariable analysis, vitamin D deficiency was independently associated with uncontrolled asthma (aOR 3.84, 95% CI 1.62–9.12; p = 0.002). Conclusion: Pakistani asthmatic children had significantly lower serum 25(OH)D than non-asthmatic controls, and lower vitamin D status was associated with greater asthma severity, poorer control and higher inhaled-corticosteroid requirement. These findings support routine assessment of vitamin D status in children with asthma and lend regional support to evaluating the effect of vitamin D repletion as adjunctive therapy.