Persistent Vitamin D Deficiency in Pediatric Patients with Cystic Fibrosis

<b>Background/Objectives:</b> Cystic fibrosis (CF) is a multisystem disease caused by CFTR gene variants, with a high prevalence of vitamin D (VitD) deficiency despite the supplementation and schedules specifically developed for this population. Lower VitD levels have been associated with an increased risk of respiratory infections and pulmonary exacerbations in CF, with some pilot studies indicating the potential benefits of supplementation during acute episodes. This study aimed to describe the occurrence of VitD deficiency according to the supplemented dose in pediatric patients with CF. <b>Methods</b>: A cross-sectional analytical study was conducted to assess serum VitD levels in a pediatric population with cystic fibrosis. Clinical and biochemical data were collected, along with information on VitD intake and pancreatic enzyme dosage at the time of evaluation. <b>Results</b>: A total of 48 patients were included in the study. Normal VitD levels were observed in 41.7% of the patients, insufficiency in 31.3%, and deficiency in 27%. The median VitD intake was 2050 IU. A statistically significant difference was observed in patients with a daily intake exceeding 2000 IU. Only 10% of patients achieved levels above 30 ng/mL with a lower dose. No statistically significant association was identified between the pancreatic enzyme dosage and vitamin D levels. <b>Conclusions:</b> Vitamin D deficiency/insufficiency is a persistent problem in the pediatric CF population; the interventions targeting factors associated with this condition are required to refine supplementation schedules. These findings underscore the need for personalized strategies to optimize vitamin D status in PwCF. Ideally, these strategies should consider all associated factors, including genetic variants; however, with limited resources, our results suggest that a daily dose of 2000 IU of vitamin D may represent a reasonable and effective starting point for supplementation.