Objective: To determine whether weekly oral vitamin D supplementation influences growth, body composition, pubertal development or spirometric outcomes in South African schoolchildren. Design: Phase 3 double-blind randomised placebo-controlled trial (clinicaltrials.gov registration no. NCT02880982). Setting: Socio-economically disadvantaged peri-urban district of Cape Town, South Africa Participants: 1682 children of Black African ancestry attending government primary schools and aged 6-11 years at baseline. Interventions: Oral vitamin D3 (10,000 IU/week) vs. placebo for 3 years Main outcome measures: height-for-age and body mass index-for-age, measured in all participants); Tanner scores for pubertal development, spirometric lung volumes and body composition, measured in a subset of 450 children who additionally took part in a nested sub-study. Results: Mean serum 25-hydroxyvitamin D3 concentration at 3-year follow-up was higher among children randomised to receive vitamin D vs. placebo (104.3 vs. 64.7 nmol/L, respectively; mean difference [MD] 39.7 nmol/L, 95% CI 37.6 to 41.9 nmol/L). No statistically significant differences in height-for-age z-score (adjusted MD [aMD] -0.08, 95% CI -0.19 to 0.03) or body mass index-for-age z-score (aMD -0.04, 95% CI -0.16 to 0.07) were seen between vitamin D vs. placebo groups at follow-up. Among sub-study participants, allocation to vitamin D vs. placebo did not influence pubertal development scores, % predicted forced expiratory volume in 1 second (FEV1), % predicted forced vital capacity (FVC), % predicted FEV1/FVC, fat mass or fat-free mass. Conclusions: Weekly oral administration of 10,000 IU vitamin D3 boosted vitamin D status but did not influence growth, body composition, pubertal development or spirometric outcomes in South African schoolchildren.

ARM declares receipt of funding in the last 36 months to support vitamin D research from the following companies who manufacture or sell vitamin D supplements: Pharma Nord Ltd, DSM Nutritional Products Ltd, Thornton & Ross Ltd and Hyphens Pharma Ltd. ARM also declares receipt of vitamin D capsules for clinical trial use from Pharma Nord Ltd, Synergy Biologics Ltd and Cytoplan Ltd; support for attending meetings from Pharma Nord Ltd and Abiogen Pharma Ltd; receipt of consultancy fees from DSM Nutritional Products Ltd and Qiagen Ltd; receipt of a speaker fee from the Linus Pauling Institute; participation on Data and Safety Monitoring Boards for the VITALITY trial (Vitamin D for Adolescents with HIV to reduce musculoskeletal morbidity and immunopathology, Pan African Clinical Trials Registry ref PACTR20200989766029) and the Trial of Vitamin D and Zinc Supplementation for Improving Treatment Outcomes Among COVID-19 Patients in India (ClinicalTrials.gov ref NCT04641195); and unpaid work as a Programme Committee member for the Vitamin D Workshop. All other authors declare that they have no competing interests.

NCT02880982

This study was funded by the UK Medical Research Council (refs MR/R023050/1 and MR/M026639/1, both awarded to ARM).

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The trial was approved by the University of Cape Town Faculty of Health Sciences Human Research Ethics Committee (Ref: 796/2015) and the London School of Hygiene and Tropical Medicine Observational/Interventions Research Ethics Committee (Ref: 7450-2).

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