Associations between body fat and bone mineral density in children and adolescents aged 6-17 years in an urban city in China: A cross sectional study.

A cross-sectional study was conducted using a multistage cluster random sampling technique to investigate the association between body fat and forearm bone mineral density (BMD) among children and adolescents aged 6-17 years in urban China. Body fat was determined by bioelectrical impedance analysis (BIA), and forearm BMD was measured by dual-energy X-ray absorptiometry (DEXA). 342 students were included in the study. Significant positive correlations were observed between BMI and forearm BMD in boys (β=0.465, p<0.001) and girls (β=0.496, p<0.001), and between body fat and forearm BMD (boys: β=0.312, p<0.001; girls: β=0.550, p<0.001). However, these associations were no longer significant after adjusting for age (boys: β=0.089, p=0.151; girls: β=0.102, p=0.151). Forearm BMD increased progressively with age, peaking at 16 years in boys and 15 years in girls. Girls showed earlier BMD accumulation during puberty compared to boys, whereas boys exhibited higher BMD values during late adolescence. No significant differences in forearm BMD were observed across BMI groups (all p>0.05), though a downward trend in BMD with increasing BMI was noted among girls. These findings suggest that body fat may influence BMD in an age-dependent manner, highlighting the importance of early-life interventions to support optimal skeletal development.