Moderate-to-vigorous Physical Activity Modulates the Association Between Serum 25-Hydroxyvitamin D and Bone Stiffness in European Children and Adolescents

It remains unclear how serum 25-hydroxyvitamin D (25(OH)D) concentrations relate to childhood bone health. We hypothesized that 25(OH)D was inversely associated with bone turnover biomarkers and positively associated with bone stiffness. Cross-sectional analyses were performed using data from participants (2-15-year-old, 51% boys) from the Identification and Prevention of Dietary- and Lifestyle-induced Health Effects in Children and Infants Study (IDEFICS)/I.Family cohort, comprising 3,638 serum 25(OH)D measurements collected in 2007-2008 and 2012-2013 across eight European countries. A biomarker of bone forma- tion (serum osteocalcin), a biomarker of bone resorption (serum C-terminal telopeptides of type I collagen [CTx]), and stiffness index measured using calcaneal quantitative ultra- sound were considered outcomes. Linear mixed-effects models were used to adjust for con- founders (i.e., age, sex, parental education, time spent in sports club, dairy products con- sumption, sedentary behavior, height and weight z-scores), the cluster effect of country and repeated measurements. Interactions of calcium intake, moderate-to-vigorous physical ac- tivity (MVPA) and weight status with 25(OH)D on outcomes were tested. Only 1 in 3 partic- ipants reached the sufficient 25(OH) D concentration of 20 ng/mL. Sufficient 25(OH)D was associated with higher stiffness index if participants had MVPA >= 60 min/day (beta= 12.14, P < .05). Moreover, 25(OH)D was inversely associated with CTx (beta= -7.09, P < .05); this associa- tion was positive but not statistically significant among primary school children living with overweight/obesity. No interaction was observed for calcium intake. In conclusion, serum 25(OH)D and CTx were inversely associated. MVPA interacted with the positive association between 25(OH)D and bone stiffness, highlighting the importance of promoting MVPA guide- lines in future vitamin D and bone health interventions. (c) 2024 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)