Vitamin D plays an important role in enhancing mucosal immune defense, decreasing excessive inflammation, and increasing mucociliary clearance. Experimental studies have shown that vitamin D reduces inflammation of epithelial cells in airways infected with Respiratory Syncytial Virus and confers antiviral effects. Furthermore, several studies have shown lower serum vitamin D levels in hospitalized children with bronchiolitis. However, studies on the efficacy of Vitamin D supplementation for children with bronchiolitis are scarce with inconsistent findings. In this study, we aim to evaluate the efficacy of vitamin D supplementation in children with bronchiolitis.

Bronchiolitis is the most frequent lower respiratory tract infection in children under two years of age, which represents a major cause of medical visits, hospital admissions, and death. This disease predominantly affects small airways with acute inflammatory edema epithelial cells, excess mucus production, and bronchospasm. The most commonly involved organisms are Respiratory Syncytial Virus (accounting for 60% of cases), followed by Rhinovirus, Parainfluenza, Metapneumovirus, Influenza, and Adenovirus. Certain factors are associated with a higher risk of severe bronchiolitis, such as prematurity, chronic lung disease, cardiac disease, immunodeficiency, neuromuscular disease, and Down syndrome.

Diagnosis of bronchiolitis relies on a constellation of clinical manifestations, including respiratory distress and wheezing preceded by viral upper respiratory tract prodrome in children under two years of age. Common manifestations of bronchiolitis are rhinorrhea, cough, wheezing, tachypnea, and increased work of breathing, including nasal flaring, retractions, and grunting. Management of bronchiolitis is mainly supportive, aiming at maintaining adequate oxygenation and hydration.

Given the high burden of bronchiolitis and the lack of specific treatment, studies have investigated several therapeutic options. One of these potential therapies is vitamin D. Vitamin D is a fat-soluble vitamin that is mainly formed in the skin after exposure to ultraviolet rays, while less than 10% is obtained from dietary sources. Besides regulation of calcium and phosphorus homeostasis, vitamin D plays an important role in enhancing mucosal immune defense, decreasing excessive inflammation, and increasing mucociliary clearance. Vitamin D deficiency is common among children, particularly in developing countries, and has been linked to an increased risk of several diseases, including bronchiolitis, pneumonia, and otitis media.

Experimental studies have shown that vitamin D reduces inflammation of epithelial cells in airways infected with Respiratory Syncytial Virus and confers antiviral effects. Furthermore, several studies have shown lower serum vitamin D levels in hospitalized children with bronchiolitis. However, studies on the efficacy of Vitamin D supplementation for children with bronchiolitis are scarce with inconsistent findings.

In this study, we aim to evaluate the efficacy of vitamin D supplementation in children with bronchiolitis.

Inclusion Criteria:

• Age between 3 to 24 months.
• Clinical diagnosis of first episode of bronchiolitis
• First 24 hours of admission.
• Stable or decreasing requirement for oxygen on 2 measurements 2 hours apart.
• Pulse rate less than 180 beat/minute.
• Respiratory rate less than 80 breath/min.
• Oxygen supplementation < 40% Fraction of inspired oxygen or < 2 L/min by nasal prong
• Not on high flow nasal cannula, continuous positive airway pressure, or mechanical ventilation at the time of enrollment.

Exclusion Criteria:

.• History of previous episodes of wheezing.

• History of apnea
• Need for positive pressure support or high flow nasal cannula at the time of enrollment.
• Chronic lung disease (requiring home oxygen, or pulmonary hypertension)
• Cardiac disease (cyanotic, hemodynamically significant [requiring diuretics], or pulmonary hypertension).
• Neuromuscular disease.
• Metabolic disease.
• Immunodeficiency.
• Chromosomal abnormalities.
• Craniofacial malformation
• Hemoglobinopathy.
• Hypercalcemia
• Chromosomal abnormalities
• Use of large doses of vitamin D (> 400 IU/day) in the last month.

Unidentified patients' data will be available upon reasonable request after publication

After publication of the study

Unidentified patients' data will be available upon reasonable request after publication