title: The Tromsø Study: Fit Futures: a study of Norwegian adolescents' lifestyle and bone health.
abstract: Bone mass achievement predicts later fracture risk. This population-based study describes bone mineral density (BMD) levels and associated factors in Norwegian adolescents. Compared with international reference ranges, BMD levels appear higher and physical activity levels are positively associated with BMD.
  
  
  OBJECTIVE
  Norway has one of the highest reported incidences of osteoporotic fractures. Maximisation of peak bone mass may prevent later fractures. This population-based study compared BMD levels of Norwegian adolescents with international reference ranges and explored associated factors.
  
  
  METHODS
  All first-year upper-secondary school students, aged 15-19 years in the Tromsø region were invited to the Fit Futures study in 2010-2011. Over 90 % of the invited participants attended, 508 girls and 530 boys. BMD was measured at total hip, femoral neck and total body by dual X-ray absorptiometry. Lifestyle variables were collected by self-administered questionnaires and interviews. All analyses were performed sex stratified, using linear regression models.
  
  
  RESULTS
  In girls, mean BMD (SD) was 1.060 g/cm(2) (0.124), 1.066 g/cm(2) (0.123) and 1.142 g/cm(2) (0.077) at the total hip, femoral neck and total body, respectively. In boys, corresponding values were 1.116 (0.147), 1.103 (0.150) and 1.182 (0.097), with significant higher values than the Lunar pediatric reference at 16 years of age. In girls, height and self-reported intensive physical activity of more than 4 h a week and early sexual maturation were positively associated with BMD at both femoral sites (p < 0.047). Among boys age, height, body mass index, physical activity and alcohol intake were positively (p < 0.038), whereas early stages of sexual maturation and smoking was negatively (p < 0.047) related to BMD.
  
  
  CONCLUSIONS
  Despite the heavy fracture burden, Norwegian adolescents' BMD levels are higher than age-matched Caucasians. Physical activity is associated with 1 SD increased BMD levels in those involved in competition or hard training.
authors.affiliation: Department of Health and Care Sciences, UiT The Arctic University of Norway, 9037, Tromsø, Norway, anne.winther@uit.no.
authors.forename: Anne
authors.initials: A
authors.lastname: Winther
authors.forename: Elaine
authors.initials: E
authors.lastname: Dennison
authors.forename: Luai Awad
authors.initials: LA
authors.lastname: Ahmed
authors.forename: Anne-Sofie
authors.initials: AS
authors.lastname: Furberg
authors.forename: Guri
authors.initials: G
authors.lastname: Grimnes
authors.forename: Rolf
authors.initials: R
authors.lastname: Jorde
authors.forename: Clara Gram
authors.initials: CG
authors.lastname: Gjesdal
authors.forename: Nina
authors.initials: N
authors.lastname: Emaus
mesh_terms: D015502:Absorptiometry, Photon; D000293:Adolescent; D017677:Age Distribution; D000704:Analysis of Variance; D015519:Bone Density / Q000502:physiology*; D003430:Cross-Sectional Studies; D015444:Exercise / Q000502:physiology; D005260:Female; D005272:Femur Neck; D006615:Hip; D006801:Humans; D008019:Life Style; D008297:Male; D009664:Norway / Q000453:epidemiology; D058866:Osteoporotic Fractures / Q000453:epidemiology* / Q000503:physiopathology; D017678:Sex Distribution