Impact of Vitamin D Status and Supplementation on Exploratory Inflammatory Biomarkers in Preschoolers with Asthma

BACKGROUND:Vitamin D supplementation may improve asthma by modulating inflammation, but its effects in preschoolers with virus-induced asthma remain underexplored. OBJECTIVE:To measure the association between serum 25-hydroxyvitamin D (25(OH)D) and inflammatory biomarkers and the impact of vitamin D supplementation on these biomarkers. METHODS:We conducted a nested study within a 7-month randomized placebo-controlled trial. Children aged 1 to 5 years with virus-induced asthma received vitamin D3 in 2 oral boluses (100,000 IU) 3.5 months apart, with a daily (400 IU) supplement, or placebo boluses and daily supplement. Serum 25(OH)D and C-reactive protein (CRP) were measured at baseline, 3.5 months, and 7 months, whereas blood cells were measured at baseline and 7 months. Primary outcomes were CRP across time points and change from baseline in CRP at 3.5 and 7 months, analyzed using generalized estimating equation and mixed-effects models. RESULTS:Among 236 (118 Vitamin D: 118 placebo) children (64.4% male), no significant association was observed between CRP and 25(OH)D. However, neutrophils were inversely associated with 25(OH)D (adjusted β [95% CI]= -0.016 (-0.027 to -0.005) × 10⁹ cells/L, n = 198). Compared with placebo, vitamin D supplementation led to a greater reduction from baseline in CRP over time (adjusted β [95% CI] = -3.154 [-5.978 to -0.330] mg/L, n = 174), and neutrophils at 7 months (adjusted β [95% CI] = -0.657 [-1.288 to -0.026] × 10⁹ cells/L, n = 110). No associations were observed with other blood cell biomarkers. CONCLUSION:In preschoolers with virus-induced asthma, serum 25(OH)D was inversely associated with neutrophils, and vitamin D supplementation significantly reduced CRP and neutrophils over time, suggesting modulation of neutrophilic inflammation. TRIAL REGISTRATION:ClinicalTrials.gov Identifier: NCT03365687.