Association of serum 25-hydroxyvitamin D with bone health measured by calcaneal quantitative ultrasound: a large cross-sectional analysis in children and adolescents.

Background : Vitamin D plays a crucial role in bone health; however, findings in children and adolescents remain inconsistent, and few studies have examined its impact on bone health measured by quantitative ultrasound (QUS). This study aims at assessing the relationship between serum vitamin D levels and bone health, as evaluated by QUS, across varying pubertal stages and genders. Methods : A baseline cross-sectional survey of an ongoing cohort study included 4682 children and adolescents aged 6 to 18 years from Shenzhen, China. Serum levels of 25-hydroxyvitamin D (25(OH)D), which is the sum of 25(OH)D 2 and 25(OH)D 3 , were quantified using liquid chromatography-mass spectrometry. Bone health was measured through calcaneal QUS, utilizing the speed of sound (SOS) in the heel as a principal measure-a higher SOS indicating a denser bone structure. Generalized linear models were used to evaluate the association of serum 25(OH)D, 25(OH)D 2 , and 25(OH)D 3 levels with the SOS. Results : Forty-one point-one percent of this population was vitamin D deficient (serum 25(OH)D < 20 ng ml -1 ), with only 11.1% being sufficient. In the fully adjusted model, we observed a significant positive association between increased serum 25(OH)D quartiles and SOS. Compared with the participants in the lowest quartiles of serum 25(OH)D, those in successive quartiles of 25(OH)D were 3.54 (95% CI: 0.81, 6.28) m s -1 , 5.74 (95% CI: 2.87, 8.61) m s -1 , and 8.83 (95% CI: 5.83, 11.84) m s -1 , respectively ( P for trend < 0.0001). The correlations observed for serum 25(OH)D 2 and 25(OH)D 3 with SOS were similar to those of serum 25(OH)D. Importantly, this association was primarily observed in post-pubertal children and adolescents but was absent in pre- and mid-pubertal participants ( P for interaction = 0.0004). Conclusion : Elevated serum 25(OH)D levels were associated with better bone health, as measured through calcaneal QUS, in children and adolescents, particularly among those who had reached the post-pubertal stage. These findings highlight the crucial importance of maintaining sufficient vitamin D levels to support optimal bone health in this demographic.