10: Vitamin D and Fracture Risk in Early Childhood: A Case-Control Study

Vitamin D is important for bone health and may be protective against fracture risk. Few studies have evaluated the association between vitamin D and fracture risk in children and none have evaluated this association in early childhood. To evaluate if vitamin D exposures, including serum 25 hydroxyvitamin D (25[OH]D) concentration, vitamin D fortified cow's milk intake and vitamin D supplementation, were associated with fracture risk in children <6 years of age. A case-control study was conducted. Cases were recruited from a pediatric fracture clinic and matched controls were obtained from children enrolled in the TARGet Kids! primary-care research network. Controls were matched to cases on age, sex, height and season of blood draw. Serum 25(OH)D was measured using liquid chromatography tandem mass spectrometry. Typical daily cow's milk intake and vitamin D supplementation were obtained through a parent completed questionnaire. The odds of fracture risk was estimated using adjusted odds ratios (aOR) and 95% confidence intervals (CI) obtained from conditional logistic regression, with adjustment for skin type, waist circumference, outdoor free play time, neighbourhood income, soda consumption and child birth weight. A total of 206 cases were recruited from 2009-2013 and were matched to 343 controls. Serum 25(OH)D concentration was not significantly associated with fracture risk (per 10 nnmol/L increase, aOR=0.95 [95% CI 0.88 to 1.03]). Cow's milk was not associated with reduced odds of fracture (>2 cups vs. 2 cups per day aOR=1.39 [95% CI 0.86 to 2.23]). A statistically significant association was observed between child vitamin D supplementation and decreased odds of fracture (yes vs. no: aOR=0.42 [95% CI 0.27 to 0.63]). Serum 25(OH)D concentration was not associated with fracture risk among young children yet children's use of supplements containing vitamin D was associated with a 58% reduction in odds of fracture risk. Future studies are needed to understand the relationship between vitamin D supplementation and fracture risk.