Bone mineral density at age 7 years does not associate with adherence to vitamin D supplementation guidelines in infancy or vitamin D status in pregnancy and childhood: An Odense Child Cohort study

Vitamin D supplementation in infancy is recommended to prevent rickets. At the population level, its effects on bone mineralisation are largely unknown. We aimed to explore whether adherence to national vitamin D supplementation guidelines (10 µg/day up to age 2 years), supplementation at ages 5 and 7 years, and serum 25-hydroxyvitamin D (s-25(OH)D) at various time points associated with bone mineral density (BMD) at age 7 years in the Odense Child Cohort, Denmark (n=1,194). High adherence was defined as supplementation with 10 µg vitamin D 6-7 times per week during ≥ 80 % of the observation time. S-25(OH)D was analysed using liquid chromatography-tandem mass spectrometry. Total-body-less-head (TBLH) BMD was measured by dual-energy X-ray absorptiometry. At median age 18.1 months, 53.9 % (n=475/881) reported high adherence. The median s-25(OH)D was 64.7, 78.8, 46.0, and 71.8 nmol/l in early pregnancy, late pregnancy, cord blood, and at 5 years, respectively. The mean (SD) TBLH BMD at median age 7.1 years was 0.613 (0.049) g/cm2 (z-score +0.363 (0.824)). In adjusted analyses, vitamin D supplementation up to 18 months, and at 5 and 7 years, was not associated with TBLH BMD. Similarly, no robust associations were found between TBLH BMD and s-25(OH)D at any time point. No associations were found for TBLH bone mineral concentration or bone area. In this population with relatively high s-25(OH)D concentrations, no consistent associations were found between adherence to vitamin D supplementation recommendations or vitamin D status in pregnancy or childhood, and bone mineralisation at age 7 years.