title: Distinct relationships of intramuscular and subcutaneous fat with cortical bone: findings from a cross-sectional study of young adult males and females.
abstract: BACKGROUND
  Intracellular fat within muscle and visceral tissue has been suggested to adversely influence bone development.
  
  
  OBJECTIVE
  The aim of the study was to evaluate associations between im fat, as reflected by muscle density as measured by peripheral quantitative computed tomography, and cortical bone parameters in young adults.
  
  
  METHODS
  We conducted a cross-sectional analysis of 1703 males and 2243 females aged 17.8 years from the Avon Longitudinal Study of Parents and Children.
  
  
  METHODS
  We measured cortical bone parameters from midtibial peripheral quantitative computed tomography scans.
  
  
  RESULTS
  Muscle density (inversely related to im fat) was inversely associated with periosteal circumference (PC) (beta = -0.07 [95% confidence interval (CI), -0.1, -0.04]), cortical bone mineral density (BMDC) (beta = -0.21 [95% CI, -0.26, -0.17]), and cortical thickness (CT) (beta = -0.37 [95% CI, -0.42, -0.33]) (males and females combined, adjusted for age, height, gender, and muscle cross-sectional area). In contrast, sc fat area was positively associated with PC (beta = 0.10 [95% CI, 0.07, 0.12]), but no association was seen with BMDC or CT. To examine the role of candidate intermediary metabolic pathways, analyses were repeated after adjustment for insulin, C-reactive protein, and β-C-telopeptides of type I collagen. Whereas similar associations were observed after adjustment for insulin and C-reactive protein, the association between muscle density and BMDC was partially attenuated by adjustment for β-C-telopeptides of type I collagen (beta = -0.14 [95% CI, -0.20, -0.08]).
  
  
  CONCLUSIONS
  Although im and sc fat were both positively associated with cortical bone mass, the nature of these relationships differed in that im fat was predominantly associated with CT and BMDC, whereas sc fat was mainly associated with PC. These relationships were largely independent of candidate metabolic pathways, such as altered bone resorption, insulin resistance, or inflammation.
authors.affiliation: Musculoskeletal Research Unit, School of Clinical Sciences, University of Bristol, Bristol BS10 5NB, United Kingdom.
authors.forename: K
authors.initials: K
authors.lastname: Deere
authors.forename: A
authors.initials: A
authors.lastname: Sayers
authors.forename: H T
authors.initials: HT
authors.lastname: Viljakainen
authors.forename: D A
authors.initials: DA
authors.lastname: Lawlor
authors.forename: N
authors.initials: N
authors.lastname: Sattar
authors.forename: J P
authors.initials: JP
authors.lastname: Kemp
authors.forename: W D
authors.initials: WD
authors.lastname: Fraser
authors.forename: J H
authors.initials: JH
authors.lastname: Tobias
mesh_terms: D000273:Adipose Tissue / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D015519:Bone Density; D002097:C-Reactive Protein / Q000032:analysis; D024042:Collagen Type I / Q000097:blood; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007328:Insulin / Q000097:blood; D008297:Male; D009132:Muscles / Q000378:metabolism*; D010455:Peptides / Q000097:blood; D050151:Subcutaneous Fat / Q000502:physiology*; D055815:Young Adult
chemical_list: D024042:Collagen Type I; D007328:Insulin; D010455:Peptides; C052929:collagen type I trimeric cross-linked peptide; D002097:C-Reactive Protein