Clinical Effects of Probiotics Across Health Conditions: An Umbrella Review of Systematic Reviews and Meta-Analyses

Probiotics are used across gastrointestinal, infectious, neonatal, metabolic, dermatological, oral, and mental-health settings, but their clinical effects vary by strain, dose, population, and outcome. This umbrella review evaluated systematic reviews with quantitative meta-analysis published between 2018 and 2023. PubMed/MEDLINE, the Cochrane Library, Europe PMC, ScienceDirect, and citation lists were searched for human reviews comparing probiotics with placebo, usual care, or no probiotic. Twelve reviews met the eligibility criteria, and methodological confidence was assessed using AMSTAR 2 principles.

The most consistent benefits were reported for prevention of necrotizing enterocolitis in very preterm or very-low-birth-weight infants (RR 0.54, 95% CI 0.45–0.65), antibiotic-associated diarrhea in adults (RR 0.63, 95% CI 0.54–0.73), acute upper respiratory tract infection (RR 0.76, 95% CI 0.67–0.87), and persistent global symptoms in irritable bowel syndrome (RR 0.78, 95% CI 0.71–0.87). Smaller improvements were observed for functional constipation, glycated hemoglobin, depressive symptoms, pediatric atopic dermatitis, periodontal outcomes, body mass index, and liver enzymes, whereas anxiety findings were inconclusive. Adverse events were generally mild, although safety reporting was incomplete in high-risk populations. Probiotics should therefore be considered strain- and indication-specific adjuncts rather than a uniform therapeutic class.