Effects of vitamin D supplementation on acute respiratory tract infections in 6-8-year-old children: a randomized clinical trial

Eur J Nutr. 2025 May 1;64(4):170. doi: 10.1007/s00394-025-03674-1.

Abstract

Purpose: Vitamin D supplementation during winter may protect children from acute respiratory tract infections (ARTI), especially at Northern latitudes where dermal vitamin D synthesis is negligible. This study aimed to investigate our hypothesis that vitamin D supplementation would have beneficial effects on ARTI in children during extended winter.

Methods: This study includes secondary analyses from a double-blinded, randomized, clinical 24-week trial, which investigated effects of vitamin D supplementation and normal vs. high dairy protein intake on children's growth and health. Baseline visits were conducted in Copenhagen, Denmark (55⁰N) from August-October 2019 and endpoint visits February-April 2020. Parents completed illness questionnaires at baseline and every 4 weeks during the intervention. In total, 200 healthy, white 6-8-y-old children were included and randomized to 20 µg/d vitamin D3 or placebo.

Results: Parents of 189 children (100 females (53%); mean (SD) age, 7.7(0.8) years) completed all ARTI questionnaires. Baseline serum 25-hydroxyvitamin D was 79.8(17.2) nmol/L, which increased by 9.4(17.0) nmol/L in the vitamin D group and decreased by 32.7(17.4) nmol/L in the placebo group. The vitamin D-supplemented children had 17% fewer sick days due to ARTI (risk ratio (RR), 0.83; 95% CI, 0.76-0.90; P < 0.001) compared with placebo. Children also had 43% fewer days with ARTI with fever (RR, 0.57; 95% CI, 0.48-0.67; P < 0.001), vitamin D group compared with placebo. No differences were found in any of the other outcomes.

Conclusion: Vitamin D supplementation reduced the number of days with ARTI. This supports a recommendation of vitamin D supplementation during extended winter at northern latitudes.

Trial registration: Name: Effects of Milk Protein and Vitamin D on Children's Growth and Health (D-pro). Number: NCT03956732. Link: https://clinicaltrials.gov/study/NCT03956732 .

Keywords: Acute respiratory tract infections; Immune system; Pediatric; Vitamin D.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Acute Disease
  • Child
  • Denmark
  • Dietary Supplements*
  • Double-Blind Method
  • Female
  • Humans
  • Male
  • Respiratory Tract Infections* / drug therapy
  • Respiratory Tract Infections* / prevention & control
  • Seasons
  • Vitamin D* / administration & dosage
  • Vitamin D* / analogs & derivatives
  • Vitamin D* / blood
  • Vitamins / administration & dosage

Substances

  • Vitamin D
  • 25-hydroxyvitamin D
  • Vitamins

Associated data

  • ClinicalTrials.gov/NCT03956732