Correlation of body mass index and serum 25-hydroxyvitamin D levels with advanced bone age in children from northwest China: a cross-sectional study.

BACKGROUND: The relationship between advanced bone age (BA), obesity, and vitamin D status remains understudied in preschool Asian children, particularly in economically developing regions. This study examined the associations of overweight/obesity and vitamin D deficiency with advanced BA among children in northwest China. METHODS: A cross-sectional study was conducted involving 1,462 children aged 3-12 years who underwent physical examinations at Gansu Provincial Maternity and Child-Care Hospital (February 2019-October 2023). BA was assessed via left wrist X-ray using the Tanner-Whitehouse 3 (TW3) RUS (radius, ulna, and short bones) method, with inter-rater reliability verified by an intraclass correlation coefficient (ICC) of 0.92 (discrepancies resolved by a third senior pediatrician). Serum 25-hydroxyvitamin D [25(OH)D] was measured using electrochemical luminescence immunoassay [Cobas e601, Roche Diagnostics; detection range: 3-100 ng/mL; intra-batch coefficient of variation (CV) <3%; inter-batch CV <5%]. Advanced BA was defined as the difference between BA and chronological age (CA) (BA-CA; BA minus CA) >1 year. The definition of advanced BA as BA-CA >1 year is widely adopted in clinical pediatric practice in China. RESULTS: The prevalence of advanced BA was 7.9%, with significantly higher rates in girls (11.9% vs. 3.4% in boys, P<0.001), children aged 9-12 years (19.4%), and those with overweight (17.1%) or obesity (16.9%) compared to normal weight children (5.8%, P<0.001). Body mass index (BMI) was positively correlated with advanced BA (Spearman ρ=0.361, P<0.001) and exhibited moderate predictive value for advanced BA [area under the curve (AUC) =0.735; 95% confidence interval (CI): 0.684-0.786]. Overweight and obesity were associated with increased odds of advanced BA after adjustment for age and sex [overweight: odds ratio (OR) =2.49, 95% CI: 1.435-4.314, P<0.05; obesity: OR =2.33, 95% CI: 1.463-3.71, P<0.001], whereas serum 25(OH)D levels showed no significant association. CONCLUSIONS: Overweight and obesity were significantly associated with advanced BA in this cross-sectional cohort of children from northwest China, whereas no significant association was detected between serum 25(OH)D and advanced BA. These findings highlight the importance of nutritional monitoring for healthy skeletal development in economically transitioning regions.