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

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 (55 degrees N) 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 mu g/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.