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Pro9.0
Probiotics Research
Likely helps
1,027 peer-reviewed studies
What the evidence says
Probably helps
Probiotics helped in about half (17/25) of the studies that measured an effect — promising, but not unanimous.
Most evidence is from high-quality meta-analyses and randomised trials published 2012–2026 with a typical study size of 258 participants.
Based on 1,026 studies · 287 meta-analyses · 582 RCTs · 42,492 total participants
Confidence
High confidence
What the studies found
17helped3unclear5didn't help· 1001 more without graded effect data
By outcome
Digestive healthImproved gut microbiome balance and digestive regularity within 2-4 weeks · 2-4 weeks
Probably helps850 studies
Therapeutic & clinical
Likely helps173 studies
Women's healthProvides essential nutrients for healthy pregnancy · Ongoing
Mostly mechanism / observational91 studies
Depression & moodReductions in depression symptoms in clinical samples; anxiety benefit is inconsistent and strain-/population-dependent · 4-8 weeks
Likely helps53 studies
Glucose & metabolic
Likely helps50 studies
Weight management
Mostly mechanism / observational46 studies
Cognitive function
Likely helps38 studies
Anxiety & stressAnxiety evidence is mixed — meta-analyses are null in general populations, with benefit mainly in clinically diagnosed samples · 4-8 weeks
Likely helps27 studies
Immune supportMay reduce frequency and duration of respiratory infections · 4-8 weeks
Mostly mechanism / observational20 studies
Skin health
Mostly mechanism / observational20 studies
InflammationImproved digestion and regularity · 2-4 weeks
Probably helps17 studies
Liver health
Mostly mechanism / observational16 studies
Heart & blood pressure
Mostly mechanism / observational13 studies
Joint pain & arthritis
Mostly mechanism / observational10 studies
Safety profile
Mostly mechanism / observational9 studies
Cholesterol & lipids
Mostly mechanism / observational8 studies
Bone health
Mostly mechanism / observational8 studies
Sleep & insomnia
Mostly mechanism / observational6 studies
Fertility & reproductive
Mostly mechanism / observational6 studies
Energy & fatigue
Mostly mechanism / observational4 studies
Vision & eye health
Too few graded studies2 studies
By the numbers
Pulled from 76 studies with measurable effects
Likely real effects
82%
across studies
People studied
42k
typical study: 258 people
Strongest designs
869
287 pooled, 582 randomised
Showed benefit
68%
17/25 studies
How long studies ran
1–3 months
4
3+ months
1
Populations Studied
General population6
Type 2 diabetes patients2
Cancer patients2
Adults2
Active research area
1,016 studies in the last 5 years · Latest meta-analysis: 2026
201220192026
1Meta-Analysisn=703 · large study2026
In plain English: Further studies with longer follow-up durations are needed to confirm these findings and explore the long-term benefits of probiotics in this population.
Chiou YY, Chiu TY, Chen MJ. · Nutrients (2026)
Background Autoimmune diseases affect 5-10% of the global population.
Subgroup analysis revealed that in rheumatoid arthritis (RA) patients, the probiotics group showed greater improvements in IL-6, IL-1β, and TNFα compared to the controls.
In multiple sclerosis (MS) patients, the probiotics group demonstrated greater improvements in hs-CRP.
2Depression symptomsMeta-Analysisn=1,401 · large study2025
In plain English: Probiotics showed substantial reductions in depression symptoms and moderate reductions in anxiety symptoms.
Asad A et al. · Nutrition reviews (2025)
Huge benefit
← WorseNo effectBetter →
Probiotics demonstrated a significant reduction in depression symptoms (SMD: -0.96; 95% CI: -1.31, -0.61) and a moderate reduction in anxiety symptoms (SMD: -0.59; 95% CI: -0.98, -0.19).
Prebiotics did not show a significant effect on depression (SMD: -0.28; 95% CI: -0.61, 0.04).
High heterogeneity was observed across studies, and subgroup analyses indicated that study duration and probiotic formulations contributed to the variation in effect sizes.
3Intestinal barrier function improvementMeta-AnalysisCited 115×n=1,891 · large study2023
In plain English: Meta-analysis of data from a total of 26 RCTs (n = 1891) indicated that probiotics significantly improved gut barrier function measured by levels of TER (MD, 5.27, 95% CI, 3.82 to 6.72, P < 0.00001), serum zonulin (SMD, -1.58, 95% CI, -2.49 to -0.66, P = 0.0007), endotoxin (SMD, -3.20, 95% CI, -5.41 to -0.98, P = 0.005), and LPS (SMD, -0.47, 95% CI, -0.85 to -0.09, P = 0.02).
Zheng Y et al. · Frontiers in Immunology (2023)
Significant improvement in intestinal barrier markers
Reduced zonulin and endotoxin levels
Enhanced gut barrier integrity across multiple trials
4FEV1 in asthma patientsMeta-AnalysisCited 10×n=1,101 · large study2023
In plain English: Conclusion: the use of probiotics in patients with asthma can improve lung inflammation and asthma symptoms, reduce the number of asthma attacks, and have no effect on lung function.
Xie Q et al. · Nutricion hospitalaria (2023)
No clear effect
← WorseNo effectBetter →
Meta-analysis was performed using Revman 5.4 software and the combined effect was evaluated by odds ratio (OR) or mean difference (MD) and 95 % confidence interval (CI).
There was no significant difference in forced expiratory volume in the first second (FEV1) (MD = 0.11, 95 % CI: -0.05, 0.26) and FEV1/FVC (%) (MD = 0.32, 95 % CI: -1.48, 2.12).
Results: a total of ten references were included, all of which were randomized controlled studies, and a total of 1,101 people were investigated.
6Prevention of antibiotic-associated diarrheaMeta-AnalysisCited 25×n=4,691 · very large study2022
In plain English: We recommend that elderly individuals could be routinely distributed probiotics to prevent AAD development when receiving antibiotic treatment.
Zhang L et al. · BMC geriatrics (2022)
We recommend that elderly individuals could be routinely distributed probiotics to prevent AAD development when receiving antibiotic treatment.
8Oral mucositis incidenceMeta-AnalysisCited 41×n=708 · large study2022
In plain English: We recommend the use of probiotics to prevent and treat oral mucositis during cancer therapy.
Liu YC et al. · International journal of molecular sciences (2022)
Noticeable benefit
← WorseNo effectBetter →
Likely real
Three trials using Lactobacilli-based probiotics reported that the incidence of oral mucositis in the probiotic group was significantly low (risk ratio [RR] = 0.84, 95% confidence interval [CI] = 0.77−0.93, p = 0.0004).
Seven trials reported a significantly low incidence of severe oral mucositis in the probiotic group (RR = 0.65, 95% CI = 0.53−0.81, p < 0.0001).
The requirement of enteral nutrition was significantly low in the probiotic group (odds ratio = 0.34, 95% CI: 0.13−0.92, p < 0.05).
10Anxiety symptomsMeta-Analysisn=1,527 · large study2018
In plain English: Probiotics did not significantly reduce symptoms of anxiety in humans (Hedges' g = -0.12, 95% CI -0.29-0.05, p = 0.151), and did not differentially affect clinical and healthy human samples.
Reis DJ et al. · PLoS One (2018)
Probiotics reduced anxiety-like behavior in animal models, mainly in diseased animals
No significant reduction in anxiety symptoms in human clinical trials
Only L. rhamnosus showed anxiolytic effects preclinically, in under-powered analyses