Prevalence of inadequate vitamin d status and associated factors in children with cystic fibrosis.

Background: This study aimed to determine the prevalence of inadequate serum 25-hydroxyvitamin D (25(OH)D) levels in a pediatric Canadian cystic fibrosis (CF) population and to assess the effectiveness of a vitamin D supplementation protocol on improving vitamin D status. A secondary objective was to analyze factors that may be associated with inadequate 25(OH)D levels. Methods: Vitamin D supplementation, 25(OH)D levels, and factors hypothesized to be associated with 25(OH)D levels were collected through a retrospective chart review (2010 and 2011) of 96 patients (1-18 years) at one CF clinic in Canada. Adequacy of 25(OH)D was set at 75 nmol/L. Patients with inadequate 25(OH)D levels in 2010 were prescribed an additional 1000 IU/d for levels <60 nmol/L or 400 IU/d for levels 60-75 nmol/L. Results: Inadequate 25(OH)D levels were observed in 26% of patients in 2010 and 23% in 2011. After supplementation was increased for those with inadequate 25(OH)D levels in 2010 (n = 20), a significant increase in 25(OH)D levels was observed in 2011 (P = .03). Adequate status was achieved in 50% of these patients (n = 10). Age was significantly negatively associated with 25(OH)D levels in both years (P = .002). Percentage of forced expiratory volume in 1 second was significantly positively associated with 25(OH)D levels in 2011 (P = .03). Conclusion: While vitamin D supplementation was effective at increasing serum 25(OH)D, this protocol did not achieve optimal serum 25(OH)D levels in 25% of the population. Increasing age had the strongest association with 25(OH)D. Current supplementation protocols may require reevaluation based on emerging evidence and revised Cystic Fibrosis Foundation guidelines.