Context: Postmenarcheal girls and premenopausal women have 3-4% higher cortical bone density (CoD, mg/cm³) compared to boys and men, respectively. Females’ denser cortical bone is thought to serve as a calcium reservoir for reproductive needs. However, prospective data are lacking that describe CoD development and bone mineral density distribution during puberty in both sexes.

Objective: To assess maturity- and sex-differences in 20-month change of CoD and radial distribution of bone mineral density (RDBMD, mg/cm³) in early-, peri- and postpubertal girls and boys.

Design: Observational study with longitudinal and cross-sectional components

Subjects: 127 healthy children, categorised as pre-, early or postpubertal according to 20-month change in menarcheal status (girls N = 68) or Tanner Stage (boys N = 59).

Main Outcome: Measures Peripheral quantitative computed tomography was used to measure CoD and RDBMD at the tibial mid-diaphysis.

Results: The increase in average CoD was 1.9% (22.8 mg/cm³; 95% CI, 10 to 36), 2.8% (33.8 mg/cm³; 95% CI, 21 to 47) and 1.5% (55.0 mg/cm³; 95% CI, 17 to 93) greater in early, peri- and postpubertal girls compared with boys, respectively. Analysis of RDBMD revealed that all girls showed an increase in the high density mid-cortical region whereas only peripubertal girls showed an increase in the lower density subcortical region. A sex-difference in RDBMD change was noted within early- and peripubertal groups.

Conclusion: Our findings of sexual dimorphism in cortical bone density development give support to the hypothesis that female bone deposits calcium for reproductive needs by consolidation of cortical bone during puberty.