Summary:​ Women have lower areal BMD (g/cm²) than men;​ however, the women have smaller-size bones. Our study showed that women ≤ 59 years have a hip volumetric BMD by DXA 3D similar to that of men of the same age. This makes us think about the importance of taking into account bone size at the time of analyzing the sex-related differences in bone mass.

Purpose:​ Women have lower areal BMD (g/cm²) than men;​ however, these studies do not take into account that women have smaller-size bones. Recently, three-dimensional (3D) modeling methods were proposed to analyze volumetric BMD (vBMD). We want to determine the values of vBMD at the hip by DXA-based 3D modeling in a cohort of people in order to know the age- and sex-related differences.

Methods:​ A total of 2647 people of both sexes (65% women) were recruited from a large cohort (Camargo cohort, Santander, Spain). 3D-SHAPER® software (version 2.8, Galgo Medical, Barcelona, Spain) was used to derive 3D analysis from the hip DXA scans at baseline

Results:​ The differences were less pronounced for vBMD (cortical sBMD 9.3%, trabecular vBMD 6.4%, integral vBMD 2.2%) compared to aBMD (FN aBMD 11.4% and TH aBMD 13.3%). After stratifying by age (≤ 59 years, 60–69 years, 70–79 years, and ≥ 80 years), we observed in ≤ 59 years that aBMD was lower in women compared to men, at FN (0.758 [0.114] g/cm2 vs. 0.833 [0.117] g/cm²;​ p = 1.4 × 10⁻²⁰) and TH (0.878 [0.117] g/cm² vs. 0.990 [0.119] g/cm²;​ p = 4.1 × 10⁻⁴⁰). Nevertheless, no statistically significant difference was observed for integral vBMD (331 [58] mg/cm³ in women and 326 [51] mg/cm³ in men;​ p = 0.19) and trabecular vBMD (190 [41] mg/cm³ in women and 195 [39] mg/cm³ in men;​ p = 0.20).

Conclusion:​ Our results make us think about the importance of taking into account bone size at the time of analyzing the sex-related differences in bone mass.