Associations between Body Composition and Vitamin D Status in Children with Overweight and Obesity Participating in a 1-Year Lifestyle Intervention

Background: To examine associations between body composition and vitamin D status in children participating in a lifestyle intervention. Methods: Children (6–12 y, n = 101) with a body mass index (BMI)-for-age >85th percentile were randomized to six dietitian-led behavior counselling sessions or no intervention. Plasma 25-hydroxyvitamin D (25(OH)D), anthropometry, and body composition using dual-energy X-ray absorptiometry were assessed every 3 months for 1 year. For each anthropometry variable (z-scores), tertiles were created to test for differences in 25(OH)D over time (tertile-by-time), and for changes in the z-score (loss, maintain, gain)-by-time, and according to fat patterning (android vs. gynoid) using mixed effects models. Results: The baseline plasma 25(OH)D was 62.2 nmol/L (95%CI: 58.7–65.7), and none < 30 nmol/L. At 6 mo, children with gynoid fat patterning had higher 25(OH)D concentrations than in those with android fat patterning (64.5 ± 1.1 nmol/L vs. 50.4 ± 1.0 nmol/L, p < 0.003, Cohen’s f = 0.20). Children with the lowest lean mass index z-score at 9 mo had higher plasma 25(OH)D concentrations than children with the highest z-score at baseline, 3 mo, and 6 mo (p < 0.05, Cohen’s f = 0.20). No other significant differences were observed. Conclusion: In this longitudinal study, vitamin D deficiency was not present in children 6–12 y of age with obesity. Reductions in adiposity did not alter the vitamin D status.