title: Analysis of body composition in individuals with high bone mass reveals a marked increase in fat mass in women but not men.
abstract: BACKGROUND
  High bone mass (HBM), detected in 0.2% of dual-energy x-ray absorptiometry (DXA) scans, is characterized by raised body mass index, the basis for which is unclear.
  
  
  OBJECTIVE
  To investigate why body mass index is elevated in individuals with HBM, we characterized body composition and examined whether differences could be explained by bone phenotypes, eg, bone mass and/or bone turnover.
  
  
  METHODS
  We conducted a case-control study of 153 cases with unexplained HBM recruited from 4 UK centers by screening 219 088 DXA scans. A total of 138 first-degree relatives (of whom 51 had HBM) and 39 spouses were also recruited. Unaffected individuals served as controls.
  
  
  METHODS
  We measured fat mass, by DXA, and bone turnover markers.
  
  
  RESULTS
  Among women, fat mass was inversely related to age in controls (P = .01), but not in HBM cases (P = .96) in whom mean fat mass was 8.9 [95% CI 4.7, 13.0] kg higher compared with controls (fully adjusted mean difference, P < .001). Increased fat mass in male HBM cases was less marked (gender interaction P = .03). Compared with controls, lean mass was also increased in female HBM cases (by 3.3 [1.2, 5.4] kg; P < .002); however, lean mass increases were less marked than fat mass increases, resulting in 4.5% lower percentage lean mass in HBM cases (P < .001). Osteocalcin was also lower in female HBM cases compared with controls (by 2.8 [0.1, 5.5] μg/L; P = .04). Differences in fat mass were fully attenuated after hip bone mineral density (BMD) adjustment (P = .52) but unchanged after adjustment for bone turnover (P < .001), whereas the greater hip BMD in female HBM cases was minimally attenuated by fat mass adjustment (P < .001).
  
  
  CONCLUSIONS
  HBM is characterized by a marked increase in fat mass in females, statistically explained by their greater BMD, but not by markers of bone turnover.
authors: Musculoskeletal Research Unit, University of Bristol, Avon Orthopaedic Centre, Southmead Hospital, Bristol BS10 5NB, United Kingdom. celia.gregson@bristol.ac.uk
authors: Celia L
authors: CL
authors: Gregson
authors: Margaret A
authors: MA
authors: Paggiosi
authors: Nicola
authors: N
authors: Crabtree
authors: Sue A
authors: SA
authors: Steel
authors: Eugene
authors: E
authors: McCloskey
authors: Emma L
authors: EL
authors: Duncan
authors: Bo
authors: B
authors: Fan
authors: John A
authors: JA
authors: Shepherd
authors: William D
authors: WD
authors: Fraser
authors: George Davey
authors: GD
authors: Smith
authors: Jon H
authors: JH
authors: Tobias
mesh_terms: D000273:Adipose Tissue / Q000000981:diagnostic imaging*; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001823:Body Composition / Q000502:physiology*; D015992:Body Mass Index; D015519:Bone Density / Q000502:physiology*; D001842:Bone and Bones / Q000000981:diagnostic imaging*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015675:Osteocalcin / Q000097:blood; D011859:Radiography; D012737:Sex Factors
chemical_list: D015675:Osteocalcin