BACKGROUND: The adverse effects of corticosteroids on bone mineral accretion (BMA) have been well documented. Vitamin D insufficiency, a prevalent condition in the pediatric population, has also been associated with decreased bone mineral density (BMD). OBJECTIVE: We sought to determine whether children with asthma who have lower vitamin D levels are more susceptible to the negative effects of corticosteroids on BMD over time. METHODS: Children aged 5 to 12 years with mild-to-moderate asthma who participated in the Childhood Asthma Management Program were followed for a mean of 4.3 years. Total doses of inhaled corticosteroids and oral corticosteroids (OCSs) were recorded, serum 25-hydroxyvitamin D3 levels were measured at the beginning of the trial, and serial dual-energy x-ray absorptiometry scans of the lumbar spine were performed. Annual BMA rates were defined as follows: [(BMD at 4 years' follow-up - BMD at baseline)/4 years]. RESULTS: BMA was calculated for 780 subjects. In boys baseline vitamin D levels significantly modified the relationship between OCSs and BMA (vitamin D × OCS interaction, P = .023). Stratification by vitamin D levels showed a decrease in BMA with increased use of OCSs in vitamin D-insufficient boys only (P < .001). Compared with vitamin D-sufficient boys, vitamin D-insufficient boys exposed to more than 2 courses of OCSs per year had twice the decrease in BMA rate (relative to boys who were OCS unexposed). CONCLUSIONS: Vitamin D levels significantly modified the effect of OCSs on BMA in boys. Further research is needed to examine whether vitamin D supplementation in children with poorly controlled asthma might confer benefits to bone health.
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