Understanding the interplay between factors that influence bone mineral density in CF

Background and Objectives: Multiple factors affect bone mineral density (BMD) in cystic fibrosis (CF). Our aim was to perform comprehensive analyses of parameters potentially contributing to BMD. Methods: A prospective single-center study assessing BMD, and correlations with multiple parameters including pancreatic status, lung functions, 6-minute walk test (6MWT), clinical score (modified Shwachman-Kulczycki [SK] score), vitamin D, nutritional intake, hand grip strength (HGS), habitual physical activity (smart watches), and quality of life (SF-36 questionnaire). Results: Forty CF patients, mean age 18.3 ± 8.1 years, forced expiratory volume in 1 second 74.7% ± 17.9% predicted. Fifteen (37.5%) and 11 (27.5%) had osteopenia and osteoporosis, respectively. BMD was similar in pancreatic sufficient (pancreatic sufficient [PS], n = 15) and insufficient (pancreatic insufficient [PI], n = 25); median hip z score −1.5 ((−2.7)−(+0.2)) vs −1.5 ((−3.5)−(+0.7)), P =.79; spine −0.8 ((−2.2)−(+2)) vs −1.2 ((−4.4)−(+1.5)), P =.39 in PS vs PI, respectively. BMD correlated with HGS (r =.72, P <.001 hip; r =.52, P =.001 spine) and fat-free mass index (r =.81, P <.001 hip; r =.63, P <.001 spine). BMD z score correlated weakly with SK score and moderately with SF-36 general health. Data from smart watches, nutrition questionnaires, and 6MWT did not correlate with BMD. In a multivariate model, age and SK score predicted spine z score BMD. Conclusions: A substantial number of CF patients have low BMD. Similar rates in PS and PI suggest that other factors, such as disease severity, may contribute to low BMD. SK and age, which can easily be obtained even with limited resources, were the best predictors of low BMD. Further larger multicenter studies are warranted to evaluate the contribution of multifactorial etiologies to low BMD in CF.