Gender differences in bone size and bone mineral density exist already before puberty. Data from the Copenhagen School Child Intervention Study (CoSCIS).
Involverte ansatteHasselstrom H, Karlsson M, Hansen SE, Grønfeldt V, Froberg K,
Andersen LB.Submitted to Bone aug 2005.
BeskrivelseEvaluation of sex differences in peripheral bone mineral density (BMD) and bone size in 368 boys and 326 girls, mean age 6.7 ± 0.4 years, had BMD (g/cm2) evaluated by peripheral dual energy X-ray absorbtiometry in the distal forearm and os calcanei.
Girls had 2.5% higher calcaneus BMD (p<0.05), whereas boys had 4.5% higher forearm BMD than girls (p<0.001). Boys had 2.7% larger forearm width and 4.7% larger knee width (p<0.0001). Calcaneus BMD correlated with weight (r = 0.50), fat free mass (FFM) (r = 0.50), fat mass (FM) (r = 0.45), percent body fat (r = 0.29) and knee width (r= 0.46), all p<0.0001.
Adjusted for weight, no relationship remained while adjusted for FFM, the relations remained but at a lower level, than the unadjusted correlations. Forearm BMD correlated with weight (r = 0.37), FFM (r = 0.39), FM (r = 0.28), percent body fat (r = 0.14) and wrist width (r = 0.24), all p<0.0001.
Adjusted for weight and FFM separately, the relationship remained but at a lower level than the unadjusted correlations. Children measured in the spring had 3.5% greater calcaneus BMD than children measured in the winter (p<0.01).
Conclusion: Boys have higher forearm - but not calcaneal BMD and larger bone size than girls, weight is the best predictor of calcaneus BMD whereas both body weight and FFM are similar good predictors of forearm BMD.