Serum Vitamin D Status and Bone Accrual Trajectories in Adolescent Idiopathic Scoliosis: A 6-Year Prospective Cohort Study

BACKGROUND: In adolescent idiopathic scoliosis (AIS), low bone mineral density (BMD) and impaired bone qualities have been demonstrated to be an important risk factor for curve progression. This prospective cohort study evaluated associations of repeated serum 25OHD measurements with BMD and volumetric bone qualities from early adolescence to early adulthood in AIS patients with low BMD. METHODS: A total of 110 girls with AIS (aged 11-14 years, femoral neck BMD Z-score ≤ 0) were recruited (baseline) and followed up at 1, 2, and 6 years thereafter. Longitudinal data of bone parameters and serum 25OHD were analyzed using linear mixed-effect models. Patients were categorized into persistent severe Vitamin D (Vit-D) deficiency (≥ 2 measurements of 25OHD < 30 nmol/L), persistent Vit-D deficiency (≥ 2 measurements of 25OHD < 50 nmol/L), or normal groups. Difference between Vit-D status was compared using ANCOVA. RESULTS: Patients were followed from a mean age of 12.98 ± 0.85 to 19.25 ± 0.90 years. During the peripubertal period (from baseline to 2-year follow-up), higher 25OHD levels were shown to be associated with higher total volumetric BMD (0.22 mg/cm3 per unit of 25OHD (adjusted), p = 0.043). At early adulthood (6-year follow-up), persistent severe Vit-D deficiency group exhibited lower total volumetric BMD (353.55 ± 45.67 vs 398.36 ± 66.65 mg/cm3, p = 0.018), lower cortical volumetric BMD (904.59 ± 31.05 vs 922.371 ± 21.29 mg/cm3, p = 0.033), and less cortical thickness (0.92 ± 0.13 vs 1.02 ± 0.12 mm, p = 0.024). CONCLUSION: Low 25OHD is associated with suboptimal BMD and impaired volumetric bone qualities during the peripubertal period in adolescents with idiopathic scoliosis. Persistent severe Vit-D deficiency predicts poor early adulthood bone outcomes, supporting future evaluation of interventional strategies.