Effects of the COVID-19 pandemic on serum vitamin D concentration in Korean children

Social distancing policies and school closures in South Korea induced by coronavirus disease 2019 have raised concerns about a lower chance of exposure to sunlight in children and adolescents. This study investigates changes in the vitamin D status of children and adolescents following the pandemic. This retrospective study includes healthy children aged 3-18 years who visited Hanyang University Hospitals in Seoul or Guri during pre-coronavirus disease 2019 (COVID-19) and post-COVID-19 pandemic periods. August 2017 to July 2019 is defined as the pre-COVID-19 pandemic period, while the period from July 2020 to July 2021 is defined as post-COVID-19 or "during the pandemic." Propensity scores were used to match the prepandemic and pandemic groups 1:1 based on age, sex, season of blood collection, and body mass index z-score to compare vitamin D status among subjects. Among 786 eligible children, 506 were matched using propensity scores. There were no significant differences in mean serum 25-hydroxyvitamin D (25(OH) D) levels (20.1±6.5 ng/mL vs. 19.9±6.3 ng/mL, P>0.05) or vitamin D deficiency rates (53.0% vs. 54.9%, P>0.05) between the prepandemic and pandemic groups. Seasonal analysis revealed lower mean serum 25(OH)D levels during the pandemic in winter/spring seasons in comparison to these levels in subjects in prepandemic winter/spring seasons (19.1±3.8 ng/mL vs. 17.2±3.7 ng/mL, P=0.006). During the COVID-19 pandemic, Korean children and adolescents showed similar serum 25(OH)D levels and vitamin D status to the prepandemic period, with a significant decrease in these measures observed in winter/spring seasons only. Prolonged confinement, such as in pandemic circumstances, underscores the need for vigilant monitoring of vitamin D status and supplementation, particularly in high-risk seasons.