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.
Purpose: 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.