The aim of our research was to evaluate and analyze serum 25(OH) vitamin D and parathyroid hormone (PTH) levels to investigate whether vitamin D deficiency serves as a risk factor for an increased incidence of acute respiratory infections (ARI) in children. Serum PTH levels were used as an indicator of vitamin D sufficiency, as normal PTH levels require an optimal concentration of 25(OH) vitamin D. The study included 129 children, divided into five subgroups: children with acute bronchopneumonia (n=42), acute laryngotracheitis (n=7), acute bronchiolitis (n=32), acute bronchitis (n=18), and a control group (n=30). No statistically significant differences in 25(OH)D levels were observed between the overall population of children with ARI and the control group (p=0.073). However, significant differences in 25(OH)D levels were identified between the control group and children with bronchopneumonia, acute bronchitis, and laryngotracheitis (p<0.01, p<0.05). Vitamin D insufficiency was found in 28.3% of children with ARIs and 10% in the healthy group. Sufficient levels were present in 60% of healthy children and 48.5% of those with ARIs. Deficiency was observed in 4% of ARI patients and 3.3% of the control group. Regarding PTH levels, statistical significance was found between the control group and the acute bronchiolitis group, due to the high percentage of children with hypervitaminosis in this subgroup. These results highlight the crucial role of vitamin D in the onset and progression of acute respiratory tract infections in children, emphasizing its impact on their overall respiratory health.

Summary: Our study aimed to determine and analyze the serum levels of 25 (OH) vitamin D and parathyroid hormone (PTH) to assess vitamin D deficiency as a risk factor for increased morbidity of acute respiratory infections (ARI) in childhood. The changes in the serum parathormone level were used as a criterion for vitamin D sufficiency since an optimal level of 25 (OH) vitamin D is required for normal PTH values. The study included 87 children divided into four subgroups, respectively – children with acute bronchopneumonia (n=49), children with acute laryngotracheitis (n=11), children with acute bronchiolitis (n=16), and a control group (n=11). Subnormal Vit. D levels were found in the individual groups: in the bronchopneumonia group, 18 children showed evidence of insufficiency; in the group of children with laryngotracheitis, five children showed insufficiency, and one child had Vit.D deficiency; children with acute bronchiolitis showed abnormalities in vit. D levels: seven children with insufficiency and two children - with deficiency. The preliminary results showed that Vit. D status deviations are more common in children with acute respiratory infections than in healthy children.