Randomized Controlled Trial of Vitamin D3 Supplementation for Viral Upper Respiratory Tract Infections (URI) Prevention

Background: Vitamin D has been shown to be an important immune system regulator. Vitamin D insufficiency during the winter may cause increased susceptibility to infections, particularly viral upper respiratory tract infections (URIs). Objective: To determine whether vitamin D supplementation during the winter season prevents or decreases URI symptoms in adults. Methods: A randomized, double-blind, placebo-controlled trial was conducted in 162 adults. Participants were randomized to receive vitamin D3 50 mcg (2000 IU) daily or matching placebo for 12 weeks from December 2006 to March 2007. A biweekly questionnaire was used to record the incidence and severity of URI symptoms