Vitamin D deficiency in pediatric patients with cystic fibrosis: associated risk factors in the northern United States.

Objectives: Cystic fibrosis (CF) is associated with vitamin D deficiency, which can lead to adverse effects including recurrent pulmonary infections and osteoporosis. We longitudinally investigated calcifediol or 25-hydroxyvitamin D (25(OH) D) levels for our pediatric patients with CF based on the time of year as well as vitamin D supplementation dosing ranges for these patients at our CF center. Methods: We retrospectively evaluated vitamin D deficiency in our pediatric CF center for 2 years (baseline and annually) while evaluating 25(OH) D serum changes based on vitamin D supplementation, seasonality, patient age, and other factors associated with CF. Results: Vitamin D supplementation was noted to be higher than current Cystic Fibrosis Foundation dosing recommendations, and no patient experienced vitamin D toxicity. Seasonality was a strong indicator of 25(OH) D levels, especially during summer or fall. Significantly fewer patients with initially low 25(OH) D levels maintained low levels at the conclusion of the study, suggesting benefit. Older patient age and higher supplemental dosing correlated with significantly lower 25(OH) D levels. Conclusions: This study suggests that targeted intervention among pediatric patients with CF living in northern latitudes of the United States, especially older children, is needed to prevent vitamin D deficiency.