Determinants of bone mass and bone geometry in adolescent and young adult women

Bone mass and bone geometry are considered to have independent effects on b one strength. The purpose of this study was to obtain data on bone mass and geometry in young female populations and how they are influenced by body s ize and lifestyle factors. In a cross-sectional, observational study in six European countries, 1116 healthy Caucasian girls aged 11-15 and 526 women aged 20-23 participated. Their radius was scanned at the ultradistal site a nd at a site approximately 30% of the radius length from the distal end wit h dual energy X-ray absorptiometry (DXA). The following parameters were ass essed from the scans: bone mineral content (BMC), bone mineral density (BMD ), cortical wall thickness (CWT), middistal diameter (D), cortical index (C I = 2CWT/D) and the Breaking Bending Resistance Index (BBRI = (D-4 - [D-CWT ](4))/D). Calcium intake was assessed by 3-day food records and physical ac tivity by questionnaire. Body size parameters were measured by anthropometr y. All parameters showed an increasing trend with pubertal stage and age, e xcept for physical activity and calcium intake. BMC and BMD were relatively more dependent on body weight and age at menarche, whereas variation in D and the mechanical index BBRI was better explained by differences in height and grip strength. CI and CWT were relatively independent of variation in body size, whereas BMC and BBRI especially were explained for a substantial proportion (25-33% in the young adults) by body size parameters. Dietary i ntake of calcium and level of physical activity seem to contribute little t o variation in bone parameters.