Effects of vitamin D and high dairy protein intake on bone mineralization and linear growth in 6- to 8-year-old children: the D-pro randomized trial

Abstract

Background Vitamin D and dairy protein may stimulate bone mineralization and linear growth in children, but previous studies show inconsistent results and have not examined their combined effects. Objectives To investigate combined and separate effects of vitamin D supplementation and high-protein (HP) compared with normal-protein (NP) yogurt intake on children's bone mineralization and linear growth. Methods In a 2 × 2–factorial trial, 200 healthy, 6- to 8-year-old, Danish, children with light skin (55°N) were randomized to 20 µg/d vitamin D3 or placebo and to substitute 260 g/d dairy with HP (10 g protein/100 g) or NP (3.5 g protein/100 g) yogurt for 24 weeks during an extended winter. Outcomes were total body less head (TBLH) and lumbar spine bone mineral density (BMD), bone mineral content (BMC), and bone area (BA) by dual-energy X-ray absorptiometry, height, and biomarkers of bone turnover and growth. The primary outcome was TBLH BMD. Results In total, 184 children (92%) completed the study. The baseline serum 25-hydroxyvitamin D was 80.8 ± 17.2 nmol/L, which increased by 7.2 ± 14.1 nmol/L and decreased by 32.3 ± 17.5 nmol/L with vitamin D and placebo, respectively. The baseline protein intake was 15.4 ± 2.4 energy percentage (E%), which increased to 18.3 ± 3.4 E% with HP. There were no vitamin D–yogurt interactions and no main effects of either intervention on TBLH BMD. However, vitamin D supplementation increased lumbar spine BMD and TBLH BMC compared to placebo, whereas HP groups showed lower increments in lumbar spine BMD, TBLH BMC and BA, and plasma osteocalcin compared to NP groups. Height, growth factors, and parathyroid hormone levels were unaffected. Conclusions Although there were no effects on whole-body BMD, vitamin D increased bone mass and spinal BMD, whereas high compared with normal dairy protein intake had smaller incremental effects on these outcomes. This supports a recommended vitamin D intake of around 20 µg/d during winter but not use of HP dairy products for improved bone mineralization among healthy, well-nourished children. This trial was registered at clinicaltrials.gov as NCT03956732.

Vitamin D supplementation and increased dairy protein intake do not affect muscle strength or physical function in healthy 6–8-year-old children: the D-pro randomized trial

“…The study design of the D-pro trial has been described in detail elsewhere [ 18 ]. The overall aim of the D-pro study was to investigate effects of vitamin D and dairy protein on children’s growth and health.…”

“…The overall aim of the D-pro study was to investigate effects of vitamin D and dairy protein on children’s growth and health. Effects on the primary outcome, bone mineral density [ 18 ], and the secondary outcomes fat mass index, fat-free mass index (FFMI), and cardiometabolic markers have been published previously [ 19 ]. Noteworthy, we found no effects of the intervention on FFMI [ 19 ].…”

“…The intervention lasted 24 weeks and was conducted at latitude 55°N during extended winter to avoid cutaneous synthesis of vitamin D. The study was conducted at Department of Nutrition, Exercise and Sports, University of Copenhagen, Frederiksberg, Denmark. Baseline and endpoint measurements were performed during August–October 2019 and February–April 2020, respectively [ 18 ]. The study was conducted following the Declaration of Helsinki and approved by the Committees on Biomedical Research Ethics for the Capital Region of Denmark (no.…”

“…Families who responded to the invitation letter were prescreened by telephone and were subsequently invited for an information meeting together with the child. Written informed consent was obtained from all custody holders [ 18 ].…”

“…Children could not use vitamin D-containing supplements > 3 days/week the last two months and any in the month immediately preceding the start of the intervention. Finally, only one child from each household could participate in the study [ 18 ].…”