Sex, BMI, skeletal maturation, and height among children and adolescents in high-altitude Xizang: a cross-sectional study

Background Skeletal maturation influences the interpretation of childhood height, but its relationship with sex, body mass index (BMI), and attained height in children living at high altitude remains incompletely characterized. We examined concurrent associations among sex, BMI, bone-age deviation, and height relative to national reference values in children and adolescents living in Lhasa, Xizang. Methods This cross-sectional study included 199 participants aged 3–16 years (101 girls and 98 boys). Bone-age deviation was defined as bone age minus chronological age. Height difference and BMI difference were calculated relative to age- and sex-specific national reference values. Multivariable linear regression incorporated centered chronological age and its quadratic term, ethnicity, BMI difference, and pubertal status, with HC3 heteroscedasticity-consistent standard errors. Statistical indirect associations through bone-age deviation were estimated using 5,000 participant-level bootstrap resamples. Results Mean bone-age deviation was −0.64 ± 1.14 years. After adjustment, boys had a 0.65-year lower bone-age deviation than girls (95% CI, −0.96 to −0.33; P < 0.001). Each 1-kg/m² increase in BMI difference was associated with a 0.06-year increase in bone-age deviation (95% CI, 0.01 to 0.10; P = 0.010). Each 1-year increase in bone-age deviation was associated with a 2.76-cm greater height difference from the national reference (95% CI, 1.82 to 3.70; P < 0.001). The sex-related statistical indirect association through bone-age deviation was −1.78 cm (percentile 95% CI, −2.89 to −0.83; BCa 95% CI, −3.02 to −0.90). The corresponding direct association had confidence intervals spanning zero. Principal findings were generally retained in sensitivity analyses using grouped Tanner stages and after exclusion of influential or extreme observations. Conclusion In this Lhasa sample, boys showed greater skeletal maturation delay than girls, and skeletal maturity was strongly associated with current height relative to national references. Higher BMI relative to the corresponding reference was associated with more advanced skeletal maturation. These cross-sectional findings describe statistical associations and do not establish temporal mediation or an altitude-specific causal effect.