Do vitamin D levels affect forced expiratory flow 25-75 among children with asthma?

Background: Previous reports of association between vitamin D levels and pulmonary function based on forced expiratory volume in one second (FEV1) and ratio of FEV1 to forced vital capacity (FEV1/FVC) gave mixed results. Forced expiratory flow 25-75 (FEF 25-75) is considered a sensitive parameter in children as it is effort independent.
Objectives: To assess the correlation between serum vitamin D levels and pulmonary function parameters in children with asthma.
Method: This cross-sectional analytic study was conducted at the paediatric respiratory clinic of a tertiary care referral hospital. Children aged 6-12 years, having asthma, on controllers with good compliance and under regular follow-up were enrolled.
Results: Mean serum vitamin D level (16.8± 6.69ng/ml) was low and deficiency was seen in 36 (72%) children with asthma. Positive correlation (r=0.41) was seen between serum vitamin D levels and predicted FEF 25-75%. Univariate analysis between vitamin D and FEF 25-75 showed decreased vitamin D levels were associated with significantly low FEF 25-75 (p<0.001). In multivariate linear regression analysis after adjustment for age and sex, the relationship was direct and significant (R2=0.18, p<0.05) but for FEV1 the relationship was not significant (R2=-0.034, p=0.336).
Conclusions: Vitamin D levels showed direct and significant relationship with FEF 25-75 outcome in children with asthma.