Association Between Vitamin D Status and Lower Respiratory Tract Infection in Children Under Five Years of Age

Abstract

Objective: This study aimed to evaluate serum 25-hydroxyvitamin D [25(OH)D] levels in children aged 0–5 years presenting with lower respiratory tract infection (LRTI) and to investigate the association between vitamin D deficiency and infection severity. Methods: In this prospective controlled study, a total of 100 children aged 0–5 years were enrolled. The study group consisted of patients diagnosed with LRTI, while the control group included healthy children. Serum 25(OH)D, calcium, phosphorus, alkaline phosphatase (ALP), C-reactive protein (CRP), and complete blood count parameters were measured in all participants. Vitamin D status was classified as severe deficiency, deficiency, insufficiency, or normal. Statistical significance was set at p<0.05. Results: Children diagnosed with LRTI had significantly lower serum 25(OH)D levels compared to the control group (p<0.001). CRP and leukocyte levels were significantly higher in the study group (p<0.001). A significant association was observed between vitamin D deficiency and frequent infections as well as hospitalization rates. Inflammatory markers were higher in the severe vitamin D deficiency group. Additionally, serum 25(OH)D levels decreased with increasing age (p<0.001). Conclusions: Low serum 25(OH)D levels appear to be associated with increased frequency and severity of lower respiratory tract infections in early childhood. Early detection of vitamin D deficiency and maintenance of appropriate supplementation strategies may represent an important preventive approach to reducing infection burden.