Influence of Vitamin D Supplementation on Growth, Body Composition, and Pubertal Development Among School-aged Children in an Area With a High Prevalence of Vitamin D Deficiency: A Randomized Clinical Trial.

IMPORTANCE: Vitamin D deficiency (defined as 25-hydroxyvitamin D [25(OH)D] <20 ng/mL) is prevalent among children living in temperate climates and has been reported to associate independently with stunting, obesity, and early activation of the hypothalamic-pituitary-gonadal axis. Phase 3 randomized clinical trials to investigate the influence of long-term vitamin D replacement on growth, body composition, and pubertal development of school-aged children with vitamin D deficiency are lacking. OBJECTIVE: To determine whether weekly oral vitamin D supplementation influences linear growth, body composition, or pubertal development in school-aged children living in a setting where vitamin D deficiency is highly prevalent. DESIGN, SETTING, AND PARTICIPANTS: This secondary analysis of a double-blind, placebo-controlled randomized clinical trial was conducted from June 2016 to June 2019 at 18 grade schools in Ulaanbaatar, Mongolia. School-aged children (6 to 13 years at baseline) attending participating schools were included. Exclusion criteria included a positive QuantiFERON-TB Gold in-tube assay result, conditions or medications associated with altered vitamin D metabolism, use of vitamin D supplements, signs of rickets, or intention to move from Ulaanbaatar within 4 years. Of 11 475 children invited to participate in the study, 9814 underwent QFT testing, and 8851 with negative results were included in the study. All but 1 participant in the placebo group completed follow-up and were included in the present analysis. Data were analyzed from November 2021 to February 2022. INTERVENTIONS: Weekly oral doses of vitamin D3, 14 000 IU, (n = 4418), or placebo (n = 4433) for 3 years. MAIN OUTCOMES AND MEASURES: Mean z scores for height for age, body mass index for age, and waist-to-height ratio; mean percentage body fat, fat mass, and fat-free mass; and mean Tanner scores for pubertal development. RESULTS: Of 8851 participants, 4366 (49.3%) were female, and 8165 (92.2%) were of Khalkh ethnicity; the mean (SD) age was 9.4 (1.6) years. A total of 8453 participants (95.5%) were vitamin D deficient at baseline, and mean end-of-study 25(OH)D concentrations among participants randomized to vitamin D vs placebo were 31.0 vs 10.7 ng/mL (mean difference, 20.3; 95% CI; 19.9-20.6). However, vitamin D supplementation did not influence mean height for age, body mass index for age, waist-to-height ratio, percentage body fat, fat mass, fat-free mass, or Tanner scores, either overall or within subgroups defined by baseline 25(OH)D concentration less than 10 ng/mL vs 10 ng/mL or greater, estimated calcium intake less than 500 mg/d vs 500 mg/d or greater, or male vs female sex. CONCLUSIONS AND RELEVANCE: In school-aged children in this study with low baseline vitamin D status, oral vitamin D3 supplementation at a dose of 14 000 IU per week for 3 years was effective in elevating 25(OH)D concentrations but did not influence growth, body composition, or pubertal development. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT02276755

Vitamin D supplements for fracture prevention in schoolchildren in Mongolia: analysis of secondary outcomes from a multicentre, double-blind, randomised, placebo-controlled trial.

BACKGROUND: Vitamin D supplementation has been shown to increase total hip areal bone mineral density in healthy children and adolescents. We aimed to investigate whether supplementing schoolchildren living in Mongolia with weekly vitamin D3 for 3 years affected fracture risk. METHODS: We did a multicentre, double-blind, randomised, placebo-controlled trial across 18 public schools in Ulaanbaatar, Mongolia. Schoolchildren were eligible if they were aged 6-13 years at screening, had a negative QuantiFERON-TB Gold In-tube assay (QFT) result, were not hypersensitive to vitamin D or immunocompromised, did not use vitamin D supplements, did not have clinical signs of rickets, and had no intention of leaving Ulaanbaatar within 3 years. Participants were randomly assigned (1:1) to receive either vitamin D (oral dose of 14 000 international units [IU] vitamin D3, once per week) or placebo for 3 years using permuted block randomisation stratified by school of attendance. Participants, care providers, and all trial staff were masked to group assignment during the intervention. Prespecified secondary outcomes were incidence of fractures and adverse events, ascertained using questionnaires. The fracture and safety analyses included participants who completed at least one follow-up fracture questionnaire. We estimated adjusted risk ratios (RRs) and 95% CIs using generalised linear models with binomial distribution and a log link function with adjustment for school of attendance. The trial is registered with ClinicalTrials.gov, NCT02276755, and the intervention ended in May, 2019. FINDINGS: Between Sept 2, 2015, and March 20, 2017, 11 475 children were invited to participate in the study and 8851 were recruited and randomly assigned to receive either vitamin D (n=4418) or placebo (n=4433). 8348 participants were included in the fracture and safety analyses (4176 [94·5%] in the vitamin D group and 4172 [94·1%] in the placebo group). Of these, 4125 (49·4%) were female, 4223 (50·6%) were male, and 7701 (92·2%) were of Khalkh ancestry. Median age was 9·2 years (IQR 8·0-10·7) and 7975 (95·5%) participants had baseline serum 25-hydroxyvitamin D concentrations less than 50 nmol/L. During a median follow-up of 3·0 years (IQR 2·9-3·1), 268 (6·4%) participants in the vitamin D group and 253 (6·1%) in the placebo group reported one or more fractures (adjusted RR 1·10, 95% CI 0·93-1·29; p=0·27). Incidence of adverse events did not differ between study groups. INTERPRETATION: Oral vitamin D supplementation at a dose of 14 000 IU/week for 3 years was safe, but did not influence fracture risk in schoolchildren living in Mongolia who had a high baseline prevalence of vitamin D deficiency. FUNDING: US National Institutes of Health