A randomized, double-blind, placebo-controlled study found consumers taking Bifidobacterium lactis Bl-04 had experienced lower risk of upper respiratory infection than a placebo group. Another probiotic blend in the study did not show results comparable to Bifidobacterium lactis Bl-04.

A separate randomized, double-blind, placebo-controlled trial found taking Lactobacillus rhamnosus GG significantly reduced risk for gastrointestinal infections; respiratory tract infections; vomiting episodes; diarrheal episodes; episodes of gastrointestinal infections that lasted >2 days; episodes of respiratory tract infections that lasted >3 days.