The impact of plasma 25-hydroxyvitamin D on pulmonary function and exercise physiology in cystic fibrosis: a multicentre retrospective study.

BACKGROUND 25-hydroxyvitamin D (25OHD) may exert immunomodulatory effects on respiratory health, which may translate to improvements in exercise physiology. Thus, we aimed to investigate whether plasma 25OHD is associated with lung function and aerobic fitness in people with cystic fibrosis (pwCF). METHODS A multi-centre retrospective review of pwCF (>9 years old) attending the Royal Hospital for Sick Children (Edinburgh) or Wessex CF-Unit (Southampton) was performed between July 2017 to October 2019. Demographic and clinical data were collected. Plasma 25OHD measured closest in time to clinical cardiopulmonary exercise testing (CPET) and/or spirometry (forced expiratory volume FEV1 % predicted) was recorded. Pancreatic insufficiency was diagnosed based on faecal elastase of <100 µg/g. We performed multiple-regression analysis with aerobic fitness outcomes [peak oxygen uptake (VO2 peak)] and FEV1 % predicted as primary outcomes. RESULTS Ninety pwCF [mean±SD age: 19.1±8.6 years, 54 (60%) children, 48 (53%) males and 88 (98%) Caucasian] were included. 25OHD deficiency and insufficiency was 15 (17%) and 44 (49%) respectively. 25OHD deficiency and insufficiency was significantly associated with pancreatic insufficiency (χ2(4.8); p = 0.02). Plasma 25OHD was not significantly associated with FEV1 % predicted [R2 = 0.06; p= 0.42; 95%; CI (-0.09 - 0.19)] or VO2peak [R2 = 0.04; p= 0.07; 95% CI (-011 - 0.005)] in all pwCF. However, 25OHD was significantly associated with both FEV1 % [R2 = 0.15; p= 0.02; 95% CI (1.99 - 2.64)] and VO2peak [R2 = 0.13; p= 0.05; 95% CI (-0.26 - (-0.005)] in the paediatric cohort. CONCLUSION We showed that 25OHD is associated with improved lung function and aerobic fitness in children and adolescents with CF. Mechanistic and high-quality prospective studies including both lung function and aerobic fitness as primary outcomes are now warranted.