RCT for vitamin D supplementation and seasonal influenza A in schoolchildren, showing 10.8% incidence in children in the vitamin D3 group compared with 18.6% in the placebo group, relative risk RR 0.58 [0.34-0.99], p
The reduction was more prominent in children who had not been taking other vitamin D supplements. RR 0.36 [0.17-0.79], p 0.006, and who started nursery school after age 3y, RR 0.36 [0.17-0.78], p
Reduced incidence of influenza B was not seen, RR 1.39 [0.90-2.15], p
Urashima et al., 1/1/2010, peer-reviewed, 6 authors.