[Association of vitamin D nutritional status with calcaneal bone mineral density in school-age children: a prospective cohort study].

Objective: To investigate the relationships between vitamin D nutritional status and the calcaneal bone mineral density (BMD) in children. Methods: Data were obtained from School-based Cardiovascular and Bone Health Promotion Program. In 2017, a total of 15 391 children aged 6-16 years in Beijing selected through stratified cluster sampling were included in the baseline survey. A follow-up investigation was conducted in 2019. The questionnaire survey, detection of serum 25-hydroxyvitamin D [25(OH)D] level and ultrasound measurement of calcaneal BMD were conducted. Multivariable linear and logistic regression models were used to analyze the relationships between baseline vitamin D nutritional status and the follow-up calcaneal BMD. Results: A total of 10 914 children aged (11.5±3.3) years (boys accounting for 49.6%) were included in the analysis. The average 25(OH)D level was (35.4±12.0) nmol/L, and the deficiency rate was 36.1%. After the adjustment for age, gender, body mass index, smoking status, alcohol use status, dairy products intake, vitamin D supplement, calcium supplement, physical activity, pubertal development, and baseline calcaneal BMD Z-score, for per 10 nmol/L increase in 25(OH)D, the follow-up calcaneal BMD Z-score increased by 0.01(P=0.041), and the OR(95%CI) of decreased calcaneal BMD Z-score after 2 years was 0.96 (0.93-1.00)(P=0.030). Compared with vitamin D adequacy, the follow-up calcaneal BMD Z-score of children with vitamin D insufficiency and deficiency decreased by 0.03(P=0.307) and 0.06 (P=0.046), and the risk of decreased calcaneal BMD Z-score after 2 years increased by 15%(P=0.037) and 21%(P=0.006), respectively (P for trend<0.05). Conclusions: Vitamin D nutritional status was closely related to calcaneal BMD, and children with adequate vitamin D nutritional status tended to obtain higher BMD. Children and adolescents are encouraged to maintain sufficient vitamin D levels, strengthen nutrition and exercise to promote bone health.