Endocrine Abstracts

JOINT3831

Introduction: Vitamin D deficiency has been repeatedly found in individuals with cystic fibrosis (CF). Therefore, substitution is recommended by all relevant professional societies. However, the effect of novel treatment strategies such as CFTR modulators on vitamin D metabolism in CF has not been extensively studied yet.

Methods: We have reviewed the medical records of all children and adolescents followed up at our tertiary care Cystic Fibrosis Center. The age, sex, pancreatic function status and CFTR modulators use were collected. The last three assessments of serum concentration of 25-hydroxyvitamin D (25-OHD) and forced expiratory volume within the first second (FEV1) were noted and the mean was calculated. Also the respective doses of vitamin D substitution in international units were recorded.

Results: There were 169 patients (89 females) actively followed at our center. Mean age was 9. 3 ± 5. 3 years. Eighty six percent (149/169) presented with pancreatic insufficiency and sixty two percent (105/169) were on CFTR modulators. The mean 25-OHD serum concentration was 74. 9 ± 18. 6 nmol/l and mean FEV1 (percent of the reference) was 100. 7 ± 14. 3. There was no difference in these two measures between pancreatic sufficient and insufficient patients and between treated and untreated with CFTR modulators. In the linear regression model, 25-OHD concentrations were only slightly negatively influenced by age (beta -1. 14 ± 0. 33, P < 0. 001) but not CFTR modulator use or pancreatic sufficiency. However, vitamin D substitution dose was positively influenced by age (beta 97. 2 ± 17. 6, P < 0. 001) and negatively by pancreatic sufficiency (beta -580. 6 ± 247. 7, P = 0. 020) but not CFTR modulators.

Conclusion: It seems that patients with CF with pancreatic insufficiency need higher doses of vitamin D to keep their 25-OHD serum concentrations within reference range, as compared to patients with pancreatic sufficiency. Despite the expected positive effect of CFTR modulators on vitamin D metabolism in CF, we could not prove that in our study. Longitudinal studies collecting data before and after commencement of the CFTR modulators may elucidate whether vitamin D doses could be decreased or maybe completely discontinued in patients with CF treated with the modern drugs.