title: A cross-sectional study of osteocalcin and body fat measures among obese adolescents.
abstract: Osteocalcin (OCN), a marker of osteoblast activity, has been implicated in the regulation of energy metabolism by the skeleton and thus may affect body fat measures.
  
  
  OBJECTIVE
  To examine the relationships of OCN to body fat measures and whether they vary according to markers of energy and vitamin D metabolism.
  
  
  METHODS
  Data were obtained from 58 obese adolescents aged 13-17.9 years (38 females, 8 black or African-American). Total fat mass (FM) [dual X-ray absorptiometry (DXA)] and visceral adipose tissue (VAT) [computerized axial tomography (CT)] were calculated. Blood tests included leptin, OCN, 25-hydroxyvitamin D [25(OH)D], parathyroid hormone (PTH), thyroid function tests, and triglycerides. Markers of glucose metabolism were obtained from fasting and OGTT samples.
  
  
  CONCLUSIONS
  Adolescents with 25(OH)D <20 ng mL(-1) were considered deficient (n = 17/58); none had high PTH (PTH ≥ 65 pg mL(-1) ). OCN was associated with lower VAT (-84.27 ± 33.89 mm(2) ) and BMI (-0.10 ± 0.05 kg m(-2) ), not FM (P = 0.597) in a core model including age, sex, race, geographic latitude, summer, height z-score, and tanner stage. Adding 25(OH)D deficiency and PTH attenuated the inverse association of OCN to VAT. There was a significant interaction of OCN and 25(OH)D deficiency on FM (0.37 ± 0.18 kg, P = 0.041) and BMI (0.28 ± 0.10 kg m(-2) , P = 0.007) in this adjusted model, which was further explained by leptin. Adding A1C to the core model modified the relationship of OCN to VAT (-93.08 ± 35.05 mm(2) , P = 0.011), which was further explained by HOMA-IR. In summary, these findings provide initial evidence for a relationship between OCN and body fat measures that is dependent on energy metabolism and vitamin D status among obese adolescents.
authors.affiliation: Boston Medical Center, Boston University School of Medicine, USA. carine.lenders@bmc.org
authors.forename: Carine M
authors.initials: CM
authors.lastname: Lenders
authors.forename: Phillip D K
authors.initials: PD
authors.lastname: Lee
authors.forename: Henry A
authors.initials: HA
authors.lastname: Feldman
authors.forename: Darrell M
authors.initials: DM
authors.lastname: Wilson
authors.forename: Stephanie H
authors.initials: SH
authors.lastname: Abrams
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Gitelman
authors.forename: William J
authors.initials: WJ
authors.lastname: Klish
authors.forename: Marcia S
authors.initials: MS
authors.lastname: Wertz
authors.forename: George A
authors.initials: GA
authors.lastname: Taylor
authors.forename: Richard T
authors.initials: RT
authors.lastname: Alongi
authors.forename: Tai C
authors.initials: TC
authors.lastname: Chen
authors.forename: Michael F
authors.initials: MF
authors.lastname: Holick
mesh_terms: D015502:Absorptiometry, Photon; D000273:Adipose Tissue / Q000737:chemistry*; D000293:Adolescent; D001741:Black or African American; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D050152:Intra-Abdominal Fat / Q000737:chemistry; D020738:Leptin / Q000097:blood; D008297:Male; D009765:Obesity / Q000097:blood*; D015675:Osteocalcin / Q000097:blood*; D010281:Parathyroid Hormone / Q000097:blood; D014807:Vitamin D / Q000097:blood
chemical_list: D020738:Leptin; D010281:Parathyroid Hormone; D015675:Osteocalcin; D014807:Vitamin D