Vitamin D status in young adults with cystic fibrosis on highly effective CFTR modulator therapy.

Vitamin D deficiency is a common pathology in people with cystic fibrosis (PwCF) due to the malabsorption of fat-soluble vitamins. Vitamin D plays an integral role in bone health and lung immunity; therefore, treating deficiencies is a clinical priority in PwCF. Highly effective modulator therapy (HEMT) improves the function of the cystic fibrosis transmembrane conductance regulator (CFTR) protein that is altered in PwCF, resulting in improved lung function and fat absorption. However, the impact of HEMT on restoring vitamin D status, a fat-soluble vitamin, has not been fully elucidated. We retrospectively examined serum 25-hydroxyvitamin D (25(OH)D) up to ten years prior in 89 young adults with CF classified based on current HEMT use (yes or no). We used two-way ANOVA to evaluate trends in both groups. Both HEMT users (n = 68) and HEMT non-users (n = 21) on average exhibited decreased serum 25(OH)D levels over ten years (-14.2 ng/mL (SI 35.4 nmol/L) and -14 ng/mL (SI 34.9 nmol/L) respectively), with no difference in change between the two groups (p = 0.44). This suggests that HEMT may not correct vitamin D status in PwCF. Further large scale prospective studies are needed to comprehensively investigate the relationship between vitamin D and HEMT.