Effect of Vitamin D supplementation on the prevention of respiratory tract infections: A Systematic Review with Meta-Analysis

Background: Vitamin D is a fat soluble vitamin mainly responsible for calcium absorption and bone mineralization. Vitamin D also has been suggested to prevent respiratory tract infections (RTIs) through studies of COVID-19 cases which hinted relations between vitamin D insufficiency or deficiency to the severity of RTIs. Purpose: To evaluate the overall effect of Vitamin D supplementation on the prevention of respiratory tract infections (RTIs) and serum 25(OH)D concentration before and after intervention based on clinical studies published from 2009 to 2019, in order to propose interventions that can reduce the risk, severity, and mortality of RTIs. Methods: Clinical trials were searched from 7 major scientific databases. 164 studies were imported into Covidence and 13 duplicates were identified. Data from 18 trials (n = 11,183) were included to assess the effect of vitamin D supplementation on RTIs incidence. A random-effects model was used to calculate odds ratios (ORs) with 95% confidence. Results: Regarding the respiratory tract infections outcome, the pooled OR for RTIs prevention was 0.74 (95% CI: 0.60–0.92, p < 0.01), indicating a statistically significant reduction in RTIs incidence with vitamin D supplementation. Subgroup analysis demonstrated notable protective effects in participants with baseline vitamin D deficiency (OR: 0.43; 95% CI: 0.25–0.72). However, results varied across studies, with some studies reporting no significant benefit. Moderate heterogeneity was observed (I² = 57%, p = 0.002), reflecting variability in study populations, dosing regimens, and durations. Conclusions: Vitamin D supplementation significantly reduces the risk of RTIs, particularly in Vitamin D deficient populations. Findings suggest that addressing vitamin D deficiency through supplementation could be an effective public health strategy to reduce RTIs incidence. Further studies are needed to determine optimal dosing and target populations.