Bone Mineral Accretion is Increased During Winter and is Positively Related to Lean Mass Accretion and Calcium Intake in Healthy Children 2–8 y

In young children, it is not well understood how bone mineral accretion is related to lean mass accretion and vitamin D metabolites. Thus, the objective of this study was to explore over 12 mo how bone parameters relate to lean mass parameters and vitamin D metabolites in children 2–8 y. This was a secondary analysis of data from 2 clinical trials (clinicaltrials.gov: NCT02097160, NCT02387892) in Montreal. Children 2–8 y consumed their normal vitamin D intake for 12 mo starting in Apr 2014 (n=21) with 4 study visits (Apr and Oct 2014, Jan and Apr 2015). At all 4 time-points, serum vitamin D status (total serum 25(OH)D: Liaison, Diasorin and LC-MS/MS) was measured and at 6, 9 and 12 mo, bone biomarkers were measured (Liaison, Diasorin, IDS iSYS) followed by standardized anthropometry, demographics plus activity and dietary questionnaires. Whole body bone mineral content (BMC) bone mineral density (BMD), and body composition parameters were measured at baseline, 6 and 12 mo and lumbar spine (L1–L4) BMC and BMD was available at 6 and 12 mo using dual-energy x-ray absorptiometry (Hologic Discovery, APEX software version 13.3). Linear regression and a mixed model ANOVA were used. In Apr 2014, children were 5.0 ± 1.9 y (range 2.2 – 7.7 y), 52% (11/21) male, with BMI Z-score of 0.79 ± 0.90. All but 1 child had 12 mo average physical activity meeting the 60 min/d guidelines. Fifty percent of children (10/20) had 12 mo average calcium intakes meeting the RDA and no children had 12 mo average vitamin D intakes meeting the RDA. However, 80% (16/20) of children maintained serum 25(OH)D ≥ 50 nmol/L over the 12 mo. Height velocity was not significantly different between summer and winter (0–6 mo: 0.61 ± 0.09 cm/mo, 6–12 mo: 0.57 ± 0.13 cm/mo). The % change in whole body BMC increased (p<0.01) during winter (Figure 1A). Mean winter % change of the lumbar spine BMC was also positive (whole body: 6.5 ± 2.8%, lumbar spine: 8.0 ± 5.8%). In line with this, bone formation biomarkers increased from 6–12 mo (p< 0.05) (Figure 1B, C) whilst bone resorption markers did not change (p> 0.05) (Figure 1D, E). Using linear regression, there was a 5.5% higher winter lumbar spine bone mineral accretion for every 5% increment of summer % change in lean mass (r2=0.76). Similarly, there was a 2.5% higher winter whole body BMC % change for every 5% increment in 12 mo % change in lean mass (r2=0.77). In regression models for lumbar spine winter % change (r2=0.76) and 12 mo whole body % change (r2=0.62) in BMC, for every increment of 200 mg of calcium intake/1000 kcal, BMC % change was higher by 1%. Twelve month changes in 25(OH)D (Figure 1F) were relatively homogenous among children, which may explain why 25(OH)D was not a significant contributor to changes in whole body and lumbar spine BMC. Our results suggest that winter bone mineral accretion may be positively and temporarily related to lean mass accretion in the preceding seasons, in addition to dietary calcium intake in children 2–8 y. Studies are needed to further elucidate the extent of delays in bone mineral accrual in response to lean mass accrual in young children. Support or Funding Information Funding from Dairy Farmers of Canada, The Canada Foundation for Innovation and Canada Research Chairs Bone mineral (BMC) % Δ (Panel A) in summer and winter. Osteocalcin, type 1 procollagen N-terminus propepetide (P1NP) and c-terminal telopeptide (CTX) at 6, 9 and 12 mo (Panels B–D). Parathyroid hormone (PTH) and 25(OH)D at all 4 time points (Panels E, F). a,b Different superscripts depict significant differences (p< 0.05), using a mixed model ANOVA. Apr 2014, Oct 2014 and Jan 2015: n=21, Apr 2015: n=19. Data are mean (SD) as a group and individual participant data over time.

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