Review: In children and adults, vitamin D3 supplementation reduces risk for acute respiratory tract infection

Included studies compared oral vitamin D3 supplementation with placebo, had research ethics approval, and prospectively collected data on ARTIs as a prespecified efficacy outcome.Long-term follow-up reports of primary randomized controlled trials (RCTs) were excluded. Primary outcome was ARTI. Other outcomes included upper ARTI, lower ARTI, ARTI-related hospitalization or emergency department visit, mortality, serious adverse events, and vitamin D–related adverse reactions (hypercalcemia or renal stones). PROSPERO International Prospective Register of Systematic Reviews CRD42014013953.