Vitamin D and Respiratory Tract Infections: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Systematic review and meta-analysis of 11 randomized controlled trials involving 5660 participants. Included populations ranged from infants to adults and included both healthy individuals and patients with various health conditions.

Oral vitamin D supplementation, primarily cholecalciferol (vitamin D3), was evaluated across regimens including 1600 IU/day daily dosing and several large bolus schedules such as 100,000 IU every 4 weeks, 100,000 IU as a single dose, 100,000 IU every 3 months, and 200,000 IU initially followed by 200,000 IU after 1 month and then 100,000 IU monthly. Comparators were the corresponding control conditions in the randomized trials.

Vitamin D supplementation reduced the risk of respiratory tract infections overall, with an OR of 0.64 (95% CI, 0.49 to 0.84; p = 0.0014). Daily dosing appeared more protective than bolus dosing, with OR 0.51 (95% CI, 0.39 to 0.67) versus OR 0.86 (95% CI, 0.62 to 1.20). Heterogeneity was substantial (Cochran's Q = 35.7, p < 0.0001, I2 = 72%). Reported adverse events and serious adverse events were not considered related to the study drug.

The evidence was limited by substantial between-study heterogeneity, different dosing regimens, and broad variation in participant age and health status. The review also noted potential publication bias, and active-arm sample sizes were not specified in the extracted source packet.