title: Body composition, lung function, and prevalent and progressive bone deficits among adults with cystic fibrosis.
abstract: BACKGROUND
  Cystic fibrosis (CF) is associated with osteoporosis and incident fracture. This study assessed independent predictors of baseline and 2-year changes in bone mineral density (BMD) in adults with CF.
  
  
  METHODS
  Sixty-four adult patients with CF, ages 18-57, were recruited from the Massachusetts General Hospital Cystic Fibrosis Care Center. Dual-energy X-ray absorptiometry (DXA) was performed at the spine and radius at baseline and 2 years (in 39 subjects). Estimates of fat-free mass index (FFMI) and fat mass index (FMI) were determined using height, weight, and tetrapolar bioelectric impedance analysis. All subjects completed lung spirometry within 1 month of the study visit. Linear regression models evaluated predictors of baseline BMD Z-scores and change in PA spine BMD Z-score over 2 years. Two definitions of low BMD were studied based on Z-score (≤-1.0 and ≤-2.0).
  
  
  RESULTS
  Low BMD was present in 52% of subjects. Subjects with low BMD were more likely to be male (67% vs. 32%, P=0.009), were more likely to be currently using glucocorticoids (21% vs. 0%, P<0.001), had lower percent body fat (P=0.04), and were more likely to have had a previous fracture (60% vs. 46%, P=0.007). In multivariable models, greater FFMI and height, but not greater FMI, were associated with greater BMD. In multivariable models, low forced vital capacity (FVC) and greater FMI were associated with greater loss of BMD at the PA spine over two years.
  
  
  CONCLUSIONS
  Male sex, short stature, and low lean mass are associated with low BMD in CF. Greater adiposity and lower lung function are predictors of negative change in BMD Z-score over 2 years.
authors.affiliation: Division of Rheumatology, Philadelphia VA Medical Center, 3900 Woodland Avenue, Philadelphia 19104, United States; Division of Rheumatology, University of Pennsylvania, 3600 Spruce Street, Philadelphia PA 19104, United States; Department of Biostatistics and Epidemiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia 19104, United States. Electronic address: bakerjo@uphs.upenn.edu.
authors.forename: Joshua F
authors.initials: JF
authors.lastname: Baker
authors.affiliation: Endocrine Unit, Department of Medicine, Massachusetts General Hospital, Boston 02114, United States; Division of Endocrinology, Boston Children's Hospital, Boston 02114, United States.
authors.forename: Melissa S
authors.initials: MS
authors.lastname: Putman
authors.affiliation: Poliklinik fuer Rheumatologie, University Hospital Schleswig-Holstein, Campus Luebeck, 23562 Lübeck, Germany.
authors.forename: Karen
authors.initials: K
authors.lastname: Herlyn
authors.affiliation: Mattina R. Proctor Diabetes Center, Mercy Hospital, Portland 04106, United States.
authors.forename: Angela Pizzo
authors.initials: AP
authors.lastname: Tillotson
authors.affiliation: Endocrine Unit, Department of Medicine, Massachusetts General Hospital, Boston 02114, United States.
authors.forename: Joel S
authors.initials: JS
authors.lastname: Finkelstein
authors.affiliation: Division of Rheumatology, University of Pennsylvania, 3600 Spruce Street, Philadelphia PA 19104, United States; Department of Biostatistics and Epidemiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia 19104, United States.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Merkel
mesh_terms: D050154:Adiposity; D000293:Adolescent; D000328:Adult; D001823:Body Composition; D015519:Bone Density; D003550:Cystic Fibrosis / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology*; D018450:Disease Progression; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010024:Osteoporosis / Q000209:etiology / Q000503:physiopathology*; D012129:Respiratory Function Tests; D055815:Young Adult
keywords: Bone mineral density; Cystic fibrosis; Dual-energy X-ray absorptiometry; Fat mass; Fat-free mass; Pulmonary function test