Vitamin D status and functional health outcomes in children aged 2-8 y: a 6-mo vitamin D randomized controlled trial

Background: Most Canadian children do not meet the recommended dietary intake for vitamin D. Objectives: The aims were to test how much vitamin D from food is needed to maintain a healthy serum 25-hydroxyvitamin D-3[25(OH)D-3] status from fall to spring in young children and to examine musculoskeletal outcomes. Design: Healthy children aged 2-8 y (n = 51) living in Montreal, Canada, were randomly assigned to 1 of 2 dietary vitamin D groups (control or intervention to reach 400 IU/d by using vitamin D-fortified foods) for 6 mo, starting October 2014. At baseline and at 3 and 6 mo, anthropometric characteristics, vitamin D metabolites (liquid chromatography-tandem mass spectrometry), and bone biomarkers (IDS-iSYS, Immunodiagnositc Systems; Liaison; Diasorin) were measured and physical activity and food intakes surveyed. At baseline and at 6 mo, bone outcomes and body composition (dual-energy X-ray absorptiometry) were measured. Cross-sectional images of distal tibia geometry and muscle density were conducted with the use of peripheral quantitative computed tomography scans at 6 mo. Results: At baseline, participants were aged 5.2 +/- 1.9 (mean +/- SD) y and had a body mass index z score of 0.65 +/- 0.12; 53% of participants were boys. There were no differences between groups in baseline serum 25(OH)D-3 (66.4 +/- 13.6 nmol/L) or vitamin D intake (225 +/- 74 IU/d). Median (IQR) compliance was 96% (89-99%) for yogurt and 84% (71-97%) for cheese. At 3 mo, serum 25(OH)D-3 was higher in the intervention group (P < 0.05) but was not different between groups by 6 mo. Although lean mass accretion was higher in the intervention group (P < 0.05), no differences in muscle density or bone outcomes were observed. Conclusions: The consumption of 400 IU vitamin D/d from fall to spring did not maintain serum 25(OH)D-3 concentration or improve bone outcomes. Further work with lean mass accretion as the primary outcome is needed to confirm if vitamin D enhances lean accretion in healthy young children.