O2085: The Role of BMI in Vitamin D Deficiency and Pediatric Fracture Healing

Background: The influence of obesity on bone health remains uncertain. While some studies show a positive correlation between body mass index (BMI) and bone mineral density, obesity also poses a fracture risk. Vitamin D deficiency is hypothesized to increase fracture risk and delay healing, often displaying an inverse correlation with BMI. This study investigates the relationship between BMI, Vitamin D levels, and pediatric fracture healing time.

Methods: A retrospective review of pediatric patients (ages 0-17) with extremity fractures and Vitamin D levels recorded within a year of injury was conducted from January 2015 to May 2022. Osteogenesis Imperfecta cases were excluded. Data were collected on demographics, medical history, injury characteristics, treatment, outcomes, Vitamin D levels, and supplementation. Vitamin D levels were defined as low (i.e., serum levels < 30 ng/ml) and normal (i.e., serum levels ≥30 ng/ml). BMI percentiles were calculated using the Center for Disease Control and Prevention’s Child and Teen BMI calculator. Spearman Correlation and Chi2 tests were used to compare BMI and Vitamin D. Kaplan-Meier curves, and Log-Rank tests were used for healing time and subgroup analysis.

Results: A total of 134 fracture cases among 121 patients were included. Mean age was 8.5 (±4.8) years, and 62.0% (N = 75) of patients were male. Normal BMI was recorded in 38.8% (n = 52) of cases, obesity in 32.1% (n = 43), overweight in 17.9% (n = 24) and underweight in 11.2% (n = 15). Low Vitamin D levels were observed in 64.2% (n = 86) of cases. A weak negative correlation existed between BMI percentile and Vitamin D levels (p = 0.023). This was supported by a significant association between BMI and Vitamin D categories, where 86.0% (n = 37) of obese, 66.7% (n = 10) of underweight, and 54.2% (n = 13) of overweight patients had low Vitamin D levels (p = 0.002). No significant difference in clinical or radiographic healing times emerged across BMI categories. Normal BMI patients with low Vitamin D levels healed slower clinically (55.0 vs. 38.0 d, p=0.006) and radiographically (83.0 d vs. 39 d, p=0.002) than in normal Vitamin D patients. Similarly, overweight BMI patients with low Vit D levels also healed slower than their normal Vitamin D counterparts clinically (74.0 vs. 47.0 d, p=0.037) and radiographically (101.0 vs. 35.0 d, p=0.012).

Conclusion: An overwhelming majority of non-normal BMI patients in this cohort presented with concomitantly low levels of Vitamin D. Although no notable variance in fracture healing duration was noted among BMI categories, patients with low vitamin D levels tended to have longer healing times in overweight patients. As such, understanding the impact of obesity and Vitamin D deficiency on fracture healing may guide treatment recommendations.