Abstract
OBJECTIVES AND STUDY: To explore the effects and mechanisms of lactoferrin combined with Bifidobacterium animalis subsp. lactis BB-12 on Respiratory tract infections (RTIs) in healthy children through a randomized, double-blind, placebo-controlled trial. METHODS: Eligible healthy children aged 0-6 years were randomized into intervention group (IG, n = 60, receiving lactoferrin and probiotic for 3 months) and control group (CG, n = 34, receiving placebo). The study primarily assessed changes in the incidence and severity of RTIs, and monitored gastrointestinal adverse events. Fecal samples were collected pre- and post-intervention to analyze gut microbiota composition and metabolomic profiles, including short-chain fatty acids (SCFAs). RESULTS: After the intervention, the incidence of RTIs showed no significant difference between groups (55% vs. 61.8%, p = 0.52), but both the RTI severity score (3.0 vs. 4.0, p < 0.05) and mean duration per RTI episode (3.54 d vs. 5.27 d, p < 0.05) were significantly lower in the IG. No serious adverse events were reported, and the incidence of indigestion was significantly reduced in the IG compared with the CG (8.3% vs. 23.5%, p = 0.04). The intervention significantly altered phylogenetic diversity (PD-whole tree within IG: p = 0.0011; baseline between IG and CG: p = 0.63; post-intervention between IG and CG: p = 0.029) and community structure (weighted UniFrac within IG: 0.012; between IG and CG at 3 months: p = 0.036 vs. baseline p = 0.01). The gut microbiota in the intervention group exhibited a trend toward greater stability over time. Integrated microbiome-metabolite analysis showed attenuation of fatty acid oxidation-and energy metabolism-related metabolic drivers after intervention, together with no significant changes in fecal SCFA levels. CONCLUSIONS: The intervention improved clinical outcomes and induced phylogenetic restructuring of the gut microbiota rather than changes in overall abundance, accompanied by a shift toward greater stability in gut microbial structure and energy metabolic patterns. CLINICAL TRIAL REGISTRATION: identifier ChiCTR2500111308.