To determine the prevalence of vitamin D deficiency (25-hydroxy vitamin D [25-OHD] levels in plasma <30 ng/mL) in pediatric patients with cystic fibrosis (CF), elucidate contributing factors for vitamin D deficiency, and determine the efficacy of ergocalciferol repletion strategies.

Retrospective chart review of 262 pediatric patients from January 2003 to December 2006 with linear and logistic regression analyses.

Vitamin D deficiency prevalence declined in the years studied from 86.5% to 46.2%. Patients >12 years old were more likely to have deficiency than patients <5 years old (odds ratio [OR], 3.44; 95% CI, 1.73-6.84). Levels obtained in spring and summer were less likely to be deficient compared with those obatined in fall (OR, 0.24; 95% CI, 0.10-0.61; and OR, 0.25; 95% CI, 0.11-0.61; respectively). Success of treatment with 50 000 IU of ergocalciferol once, twice, or 3 times weekly was 33%, 26%, and 43%, respectively. Ergocalciferol, when compared with no treatment, did not significantly increase the proportion of patients with follow-up levels ≥30 ng/mL (χ²P value = .80, .34, and .22, respectively).

The prevalence of vitamin D deficiency is high, but declined with time. Age, forced expiratory volume in 1 second, and season were associated with 25-OHD levels. Despite 33% of patients responding to 50 000 IU of ergocalciferol once a week, this recommendation does not adequately treat most patients with CF who have vitamin D deficiency.