Longer survival in cystic fibrosis has led to more bone complications. One hundred thirty-six young patients were studied for 12-24 months. Low BMD was found in 66%. Fat mass and lean mass were also reduced. Impaired pulmonary function and total steroid dose had the greatest negative influence on bone.

Introduction: Low BMD is reported as a frequent complication in adult patients affected by cystic fibrosis (CF), but the available data are less consistent for younger patients.

Materials and Methods: This study was designed to evaluate BMD longitudinally over 12-24 months in a sample of 136 young patients (3-24 years of age) and to investigate its major determinants. BMC and body composition were also evaluated.

Results: BMD (expressed as Z score) of spine and of total body was reduced in 66% of patients. The prevalence of low BMD was the same in children, adolescents, and young adults. The main determinants of BMD were forced expiratory volume in 1 s (FEV₁; as an index of pulmonary function), puberty, platelet count (as an index of portal hypertension), and cumulative steroid dose. Changes of FEV₁ over time influenced BMD changes. Bone mass, fat mass (FM) and fat-free (lean) mass (FFM) were reduced in CF patients at both total body and subregions (trunk, limbs). Lean mass influenced BMD of total body and lower limbs, whereas fat mass (and BMI) influenced spine BMD. FEV₁ also influenced FFM.

Conclusions: Low BMD was present in a significant proportion of CF patients, independent of sex and age. BMD depended on pulmonary function, steroid dose, and presence of advanced liver disease. Pulmonary function and puberty were the main stimuli for the increase of BMD over time. CF also altered body composition, and FFM was influenced by pulmonary function.