Variations of 25-Hydroxyvitamin D Levels During COVID-19 Pandemic and its Relation to Season, Sex and Age in Children

We aimed to investigate variations in vitamin D levels (VDLs) during the coronavirus disease-19 pandemic and their relationship to season, sex, and age in otherwise healthy children and adolescents. We conducted a retrospective cross-sectional study at an outpatient pediatric clinic, which included 4,262 children aged 1-18 years. The study cohort was divided into three groups: Group 1 (pre-pandemic), Group 2 (pandemic), and Group 3 (post-pandemic). Vitamin D deficiency (VDD) was defined as a level below 12 ng/mL, insufficiency as a level between 12 and 20 ng/mL, and sufficiency as a serum level above 20 ng/mL. The pandemic cohort exhibited significantly lower VDLs compared with both the pre-pandemic and post-pandemic cohorts. Females had significantly lower VDLs than males. The prevalence of VDD was highest among adolescents. A significantly higher rate of VDD was observed in the pandemic group among the 6-11 and 12-18 age groups compared with both the pre-pandemic and post-pandemic groups. VDLs were significantly lower in spring and winter than in summer and autumn. Additionally, an inverse relationship was observed between age and VDLs. Our study revealed a significant prevalence of VDD in school-aged children and adolescents, with a notable decrease in VDLs observed during the pandemic compared with other time periods. Furthermore, our study highlighted the increased vulnerability of female adolescents to VDD.