Assessing the Impact of Vitamin D Supplementation on Respiratory Infections in Children and Adolescents: A Cross-Sectional Study

Background and Objectives: Recent studies suggest that vitamin D supplementation and higher serum 25-hydroxyvitamin D (25-OHD) concentrations may reduce the incidence of respiratory infections in children and adolescents. This cross-sectional study aimed to evaluate the association between different concentrations of vitamin D supplementation, serum 25-OHD concentrations, and the frequency of respiratory infections among individuals aged 1 to 18 years, for a duration of 2 years. Methods: Concerning sun exposure in relation to vitamin D, the study took place in Romania, at approximately 45-degree northern latitude. A total of 194 patients were divided into groups based on weekly vitamin D supplementation (<400 IU, 400–800 IU, >800 IU), serum 25-OHD concentrations (<20 ng/mL, 20–30 ng/mL, >30 ng/mL), and age (<6 years, 6–12 years, 12–18 years). The overall incidence of respiratory infections was 41.2%. Results: Participants receiving >800 IU/week had a significantly lower incidence of infections (16.7%) compared to those receiving <400 IU/week (60.0%, p < 0.001). Similarly, participants with serum 25-OHD concentrations >30 ng/mL had an infection rate of 16.7%, compared to 61.4% in those with concentrations <20 ng/mL (p < 0.001). Age-specific analyses revealed that the protective effect of vitamin D was most pronounced in children under 6 years old. Logistic regression showed that higher vitamin D supplementation and serum 25-OHD concentrations were independently associated with reduced odds of respiratory infections (OR = 0.25 and OR = 0.22, respectively, p < 0.001). Conclusions: These findings support the potential role of vitamin D supplementation in preventing respiratory infections in the pediatric population.