Vitamin D status and adiposity in children with low-energy fractures: a prospective case-control study.

Fractures in children are influenced by both skeletal biology and mechanical factors. While alterations in vitamin D and other metabolic markers have been proposed as contributors to fracture risk, their role in predicting fractures in otherwise healthy pediatric populations remains unclear. This study aimed to determine whether biochemical markers of bone metabolism and body mass are independently associated with fracture occurrence and fracture patterns in children after low-energy trauma and to assess their impact on fracture patterns and anatomical distribution. We conducted a prospective case-control study including 100 children presenting after low-energy trauma (50 with radiographically confirmed fractures and 50 controls). Serum 25OH vitamin D (25OHD), parathyroid hormone (PTH), calcium, phosphate, and alkaline phosphatase (ALP) were measured within 1 week of presentation. Associations with fracture occurrence were assessed using multivariable logistic regression, including age, sex, body mass index z-score (BMI-z), an interaction term between 25OHD and BMI-z, and an additional exploratory model evaluating a 25OHD × season interaction. The discriminatory ability of 25OHD was evaluated using receiver operating characteristic analysis. Children with fractures had lower serum 25OHD concentrations and a higher prevalence of levels below 50 nmol/L compared with controls. Other biochemical markers were largely within normal ranges, although ALP levels were modestly higher in fracture patients. In multivariable analysis, 25OHD levels below 50 nmol/L were associated with increased odds of fracture, whereas age and BMI-z were not independently associated with fracture occurrence. However, a significant interaction between 25OHD and BMI-z was observed, indicating that the association between vitamin D status and fracture risk is influenced by adiposity. The overall discriminatory ability of 25OHD for fracture risk was modest.

conclusionLower 25OHD levels were observed in children with low-energy fractures. The association between vitamin D status and fracture risk appears to be modest and influenced by adiposity, with a more pronounced effect at higher BMI-z levels. Therefore, fracture susceptibility in otherwise healthy children is likely driven primarily by biomechanical and developmental factors rather than vitamin D status, supporting a targeted rather than routine laboratory assessment of metabolic markers in children presenting with fractures. CLINICALTRIALS: gov Identifier: NCT07143552. WHAT IS KNOWN: • Lower serum 25-hydroxyvitamin D concentrations have been reported in children with fractures, but the relationship between vitamin D status and fracture risk remains controversial. • Childhood obesity is associated with lower circulating vitamin D concentrations and may independently influence fracture susceptibility. WHAT IS NEW: • Vitamin D insufficiency (< 50 nmol/L) was associated with increased odds of low-energy fractures in children, although its overall discriminatory ability was modest. • The association between vitamin D status and fracture risk was modified by adiposity, with a stronger relationship observed in children with higher BMI-z. • Biochemical markers of bone mineralization were largely normal, supporting the concept that fracture susceptibility in otherwise healthy children is driven predominantly by biomechanical and developmental factors rather than clinically relevant metabolic bone disease.