The Role of Vitamin D in Pediatric Respiratory Diseases

Vitamin D is a pleiotropic secosteroid hormone involved in calcium-phosphate homeostasis, epithelial barrier integrity, antimicrobial defense, and adaptive immune regulation. Pediatric observational studies associate low serum 25-hydroxyvitamin D [25(OH)D] with respiratory infections, recurrent wheezing, asthma severity, impaired lung function, and reduced corticosteroid response, but the strength and consistency of these associations vary according to age, phenotype, baseline vitamin D status, comorbidities, and study design. Experimental evidence supports plausible effects on antimicrobial peptides, T-cell balance, airway smooth muscle, and glucocorticoid pathways. Interventional findings in selected trials in deficient or infection-prone children report fewer acute respiratory or otitis episodes. Several pediatric cohorts have shown clinically relevant associations between asthma control and vitamin D status, whereas a recent Cochrane review reported that people given vitamin D supplements did not have a lower risk of severe asthma attacks. This narrative review integrates mechanistic, observational, and interventional evidence relevant to pediatric wheezing, bronchial asthma, and respiratory tract infections, and discusses practical definitions of deficiency and age-appropriate supplementation. Maintaining adequate vitamin D status may contribute to optimal immune function and may be particularly relevant in children with recurrent respiratory infections, wheezing, or allergic diseases.