Decreased serum vitamin D levels in children with asthma are associated with increased corticosteroid use

Abstract

Background There is little knowledge about clinical variables associated with vitamin D (vitD) insufficiency in asthmatic children. Objective To investigate disease variables associated with vitD insufficiency in childhood asthma and interaction of vitD with corticosteroid-mediated anti-inflammatory responses. Methods We analyzed 25-hydroxyvitamin D serum levels in 100 asthmatic children to investigate relationships between 25-hydroxyvitamin D levels and patient characteristics. We determined vitD effects on dexamethasone (DEX) induction of mitogen-activated protein kinase phosphatase-1 (MKP-1) and IL-10 in peripheral blood mononuclear cells (PBMC). Results The median 25-hydroxyvitamin D serum level was 31 ng/mL. 47% of subjects had vitD levels in the insufficient range (<30 ng/mL), while 17% were vitD deficient (<20 ng/mL). Log10 IgE (p=0.01, ρ=−0.25) and the number of positive aeroallergen skin prick tests (p=0.02, ρ=−0.23) showed a significant inverse correlation with vitD, whereas FEV1% predicted (p =0.004, ρ=0.34) and FEV1/FVC ratio (p=0.01, ρ=0.30) showed a significant positive correlation with vitD. The use of inhaled steroids (p=0.0475), oral steroids (p=0.02), and total steroid dose (p=0.001), all showed significant inverse correlations with vitD. The amount of MKP-1 and IL-10 mRNA induced by vitD plus DEX was significantly greater than that induced by DEX alone (p<0.01). In an experimental model of steroid resistance where DEX alone did not inhibit T cell proliferation, addition of vitD to DEX resulted in significant dose dependent suppression of cell proliferation. Conclusions Corticosteroid use and worsening airflow limitation is associated with lower vitD serum levels in asthmatics. VitD enhances glucocorticoid action in asthmatic PBMC and enhances the immunosuppressive function of DEX in vitro. Clinical Implications Our study suggests that vitD supplementation may potentiate anti-inflammatory function of corticosteroids in asthmatics and thereby improve asthma control.