Bergman et al., PLoS One, 2013, 8:6, doi:10.1371/journal.pone.0065835 (Peer Reviewed) (meta analysis) Vitamin D and Respiratory Tract Infections: A Systematic Review and Meta-Analysis of Randomized Controlled Trials
Meta analysis of 11 placebo-controlled studies of 5660 patients. Vitamin D showed a protective effect against RTI (OR 0.64 [0.49-0.84]).The protective effect was larger in studies using once-daily dosing compared to bolus doses (OR = 0.51 vs OR = 0.86, p = 0.01). There was some evidence that results may have been influenced by publication bias.
Bergman et al., 1/1/2013, peer-reviewed, 4 authors.