Supplement

Probiotics

Probiotics are live bacteria and yeasts that join the microbes in your gut, helping with digestion, the intestinal lining, and immune signaling. People most often look at them for H. pylori infection, where the evidence is strong and abdominal pain improved, and trials also found diarrhea symptoms eased in acute gastroenteritis. That diarrhea evidence is moderate, drawn from four studies of about 1,100 people, some of them children or people on chemotherapy.

Sources: PMID 39993479; PMID 40535538

Updated 30 September 2026
How we grade
59 studies cited

Best evidence: Grade A
Conditions studied: 47
Outcomes: 215
Graded outcomes: 310915

Evidence by condition

Strong
Moderate
Limited
Very limited

47 conditions

Chemotherapy Side Effects

Chemotherapy Side Effects: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People
	Appetite Moderate Increase	Worsens (the measure goes up)	Moderate effect		227 people
	Diarrhea Symptoms	Improves (the measure goes down)		4 studies	327 people
Studies that measured diarrhea symptoms Oral probiotic supplementation to alleviate diarrhea induced by fluoropyrimidines or irinotecan-based chemotherapy: A systematic review and meta-analysis.Complement Ther Med · PMID 39993479 Evaluation of the efficacy of probiotics in the chemoradiotherapy of colorectal cancer: a meta-analysis of Randomized Controlled Trials.BMC Gastroenterol · PMID 40301781 Efficacy and safety of Saccharomyces boulardii CNCM I-745 for the treatment of pediatric acute diarrhea in China: a systematic review and meta-analysis.Front Cell Infect Microbiol · PMID 40535538 Efficacy of probiotics in reducing the duration and severity of acute gastroenteritis in children: A meta-analysis of randomized controlled trials.J Pediatr Gastroenterol Nutr · PMID 40739406
	Mucositis Symptoms	Improves (the measure goes down)		2 studies	1,055 people
Studies that measured mucositis symptoms Efficacy of probiotics in the treatment of oral mucositis in head and neck cancer patients: A systematic review and meta-analysis.Microb Pathog · PMID 38971507 The effect of probiotics on severe oral mucositis in cancer patients undergoing chemotherapy and/or radiotherapy: A meta-analysis.J Stomatol Oral Maxillofac Surg · PMID 39187039
	Weight	Improves (the measure goes down)		1 study	1,089 people
Studies that measured weight Effects of oral supplementation of probiotics on body weight and visceral fat in obese patients: a meta-analysis and systematic review.Sci Rep · PMID 39984625
	Bloating	Improves (the measure goes down)			125 people
	Constipation Signs and Symptoms	Improves (the measure goes down)			142 people
	Quality of Life	Improves (the measure goes up)			1,089 people

H. Pylori Infection

H. Pylori Infection: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People
	Abdominal Pain Moderate Improvement	Improves (the measure goes down)	Moderate effect		5,036 people
	Diarrhea Symptoms	Improves (the measure goes down)		4 studies	5,036 people
Studies that measured diarrhea symptoms Oral probiotic supplementation to alleviate diarrhea induced by fluoropyrimidines or irinotecan-based chemotherapy: A systematic review and meta-analysis.Complement Ther Med · PMID 39993479 Evaluation of the efficacy of probiotics in the chemoradiotherapy of colorectal cancer: a meta-analysis of Randomized Controlled Trials.BMC Gastroenterol · PMID 40301781 Efficacy and safety of Saccharomyces boulardii CNCM I-745 for the treatment of pediatric acute diarrhea in China: a systematic review and meta-analysis.Front Cell Infect Microbiol · PMID 40535538 Efficacy of probiotics in reducing the duration and severity of acute gastroenteritis in children: A meta-analysis of randomized controlled trials.J Pediatr Gastroenterol Nutr · PMID 40739406
	Helicobacter Pylori Infection Signs	Improves (the measure goes up)		2 studies	3,707 people
Studies that measured helicobacter pylori infection signs Efficacy and safety of Saccharomyces boulardii as an adjuvant therapy for the eradication of Helicobacter pylori: a meta-analysis.Front Cell Infect Microbiol · PMID 40012609 Efficacy of probiotics regimens for Helicobacter pylori eradication: A systematic review, pairwise, and network meta-analysis of randomized controlled trials.Clin Nutr ESPEN · PMID 39642994
	Adverse Events	Improves (the measure goes down)			2,413 people
	Bloating	Improves (the measure goes down)			5,036 people
	Constipation Signs and Symptoms	Improves (the measure goes down)			5,036 people
	Nausea Symptoms	Improves (the measure goes down)			5,036 people
	Vomiting	Improves (the measure goes down)			5,036 people

H. Pylori Infection

Abdominal Pain: improves
Diarrhea Symptoms: changes; see studies
Helicobacter Pylori Infection Signs: improves

H. Pylori Infection: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People
	Abdominal Pain Moderate Improvement	Improves (the measure goes down)	Moderate effect		5,036 people
	Diarrhea Symptoms	Changes; see studies		4 studies	5,036 people
Studies that measured diarrhea symptoms Oral probiotic supplementation to alleviate diarrhea induced by fluoropyrimidines or irinotecan-based chemotherapy: A systematic review and meta-analysis.Complement Ther Med · PMID 39993479 Evaluation of the efficacy of probiotics in the chemoradiotherapy of colorectal cancer: a meta-analysis of Randomized Controlled Trials.BMC Gastroenterol · PMID 40301781 Efficacy and safety of Saccharomyces boulardii CNCM I-745 for the treatment of pediatric acute diarrhea in China: a systematic review and meta-analysis.Front Cell Infect Microbiol · PMID 40535538 Efficacy of probiotics in reducing the duration and severity of acute gastroenteritis in children: A meta-analysis of randomized controlled trials.J Pediatr Gastroenterol Nutr · PMID 40739406
	Helicobacter Pylori Infection Signs	Improves (the measure goes up)		2 studies	3,707 people
Studies that measured helicobacter pylori infection signs Efficacy and safety of Saccharomyces boulardii as an adjuvant therapy for the eradication of Helicobacter pylori: a meta-analysis.Front Cell Infect Microbiol · PMID 40012609 Efficacy of probiotics regimens for Helicobacter pylori eradication: A systematic review, pairwise, and network meta-analysis of randomized controlled trials.Clin Nutr ESPEN · PMID 39642994
	Adverse Events	Changes; see studies			2,413 people
	Bloating	Changes; see studies			5,036 people
	Constipation Signs and Symptoms	Changes; see studies			5,036 people
	Nausea Symptoms	Changes; see studies			5,036 people
	Vomiting	Changes; see studies			5,036 people

Alzheimer’s Disease

Cognition
Attention
Memory: improves

Alzheimer’s Disease: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People
	Cognition Mixed effect			4 studies	419 people
Studies that measured cognition Gaba-producing lactobacilli boost cognitive reactivity to negative mood without improving cognitive performance: A human Double-Blind Placebo-Controlled Cross-Over study.Brain Behav Immun · PMID 39163908 The effect of probiotics on select cognitive domains in mild cognitive impairment and Alzheimer's disease: A systematic review and meta-analysis.J Alzheimers Dis Rep · PMID 40034358 Efficacy of probiotic supplementation in influencing cognitive function in Alzheimer's disease: A systematic review and meta-analysis.J Food Sci · PMID 40709497 Effectiveness of probiotic supplements on cognitive function in mild cognitive impairment and Alzheimer's disease: A meta-analysis of randomized controlled trials.Gen Hosp Psychiatry · PMID 41237466
	Attention No effect		NoneNo effect		402 people
	Memory	Improves (the measure goes up)			517 people

Acute Gastroenteritis

Diarrhea Symptoms: improves
Fever: improves
Vomiting: improves

Acute Gastroenteritis: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People
	Diarrhea Symptoms Moderate Improvement	Improves (the measure goes down)	Moderate effect	4 studies	1,125 people
Studies that measured diarrhea symptoms Oral probiotic supplementation to alleviate diarrhea induced by fluoropyrimidines or irinotecan-based chemotherapy: A systematic review and meta-analysis.Complement Ther Med · PMID 39993479 Evaluation of the efficacy of probiotics in the chemoradiotherapy of colorectal cancer: a meta-analysis of Randomized Controlled Trials.BMC Gastroenterol · PMID 40301781 Efficacy and safety of Saccharomyces boulardii CNCM I-745 for the treatment of pediatric acute diarrhea in China: a systematic review and meta-analysis.Front Cell Infect Microbiol · PMID 40535538 Efficacy of probiotics in reducing the duration and severity of acute gastroenteritis in children: A meta-analysis of randomized controlled trials.J Pediatr Gastroenterol Nutr · PMID 40739406
	Fever	Improves (the measure goes up)			134 people
	Vomiting	Improves (the measure goes down)			980 people

Asthma

Asthma Symptoms: improves
Lung Function: improves
Immunoglobulin A: improves

Asthma: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People
	Asthma Symptoms Small Improvement	Improves (the measure goes down)	Small effect	2 studies	544 people
Studies that measured asthma symptoms A network meta-analysis of probiotics in the treatment of childhood asthma.Front Pediatr · PMID 41098501 Efficacy of probiotics as adjuvant therapy in bronchial asthma: a systematic review and meta-analysis.Allergy Asthma Clin Immunol · PMID 39563347
	Lung Function	Improves (the measure goes up)		1 study	438 people
Studies that measured lung function Effectiveness of Probiotics, Prebiotics, and Symbiotic Supplementation in Cystic Fibrosis Patients: A Systematic Review and Meta-Analysis of Clinical Trials.Medicina · PMID 40142300
	Immunoglobulin A	Improves (the measure goes up)			362 people
	Immunoglobulin E	Improves (the measure goes up)			372 people
	Interleukin 4	Improves (the measure goes up)			665 people

Coronary Artery Disease (CAD)

C-Reactive Protein (CRP)
Glutathione (GSH): improves
Nitric Oxide: improves

Coronary Artery Disease (CAD): outcomes studied for Probiotics
Grade	Outcome	Effect	Studies	People
	C-Reactive Protein (CRP) Mixed effect		2 studies	164 people
Studies that measured c-reactive protein (crp) Effect of probiotics on C-reactive protein levels in schizophrenia: Evidence from a systematic review and meta-analysis.Complement Ther Med · PMID 39798817 Probiotic Supplementation and Inflammatory Status in Coronary Artery Disease: A Systematic Review and Meta-Analysis.Microorganisms · PMID 41156763
	Glutathione (GSH)	Improves (the measure goes up)		120 people
	Nitric Oxide	Improves (the measure goes up)		120 people
	Oxidative Stress Biomarkers	Improves (the measure goes down)		164 people
	Total Antioxidant Capacity (TAC)	Improves (the measure goes up)		120 people

Psoriasis

C-Reactive Protein (CRP)
Psoriasis Symptoms: improves
Interleukin 6: improves

Psoriasis: outcomes studied for Probiotics
Grade	Outcome	Effect	Studies	People
	C-Reactive Protein (CRP) Mixed effect		2 studies	400 people
Studies that measured c-reactive protein (crp) Effect of probiotics on C-reactive protein levels in schizophrenia: Evidence from a systematic review and meta-analysis.Complement Ther Med · PMID 39798817 Probiotic Supplementation and Inflammatory Status in Coronary Artery Disease: A Systematic Review and Meta-Analysis.Microorganisms · PMID 41156763
	Psoriasis Symptoms	Improves (the measure goes down)	1 study	400 people
Studies that measured psoriasis symptoms The efficacy and safety of probiotics in the adjuvant treatment of psoriasis: a systematic review and meta-analysis of randomized controlled trials.Front Med · PMID 39328313
	Interleukin 6	Improves (the measure goes down)		400 people
	Quality of Life	Improves (the measure goes up)		400 people

Metabolic Health

Blood glucose: improves
HbA1c: improves
Insulin Resistance: improves

Metabolic Health: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People
	Blood glucose Small Improvement	Improves (the measure goes down)	Small effect	1 study	450 people
Studies that measured blood glucose Effects of probiotics supplementation on glycemic profile in adults with type 2 diabetes mellitus: A grade-assessed systematic review and dose-response meta-analysis of randomized controlled trials.Clin Nutr ESPEN · PMID 39349104
	HbA1c	Improves (the measure goes down)		2 studies	671 people
Studies that measured hba1c The effects of probiotic supplementation on cardiometabolic health in patients with prediabetes: a systematic review, meta-analysis, and GRADE assessment.Front Nutr · 2025 · PMID 40959695 Probiotics Supplementation for Improving Glucolipid Parameters in Individuals with Prediabetes: A Systematic Review and Meta-Analysis of Randomized Trials.Probiotics Antimicrob Proteins · PMID 39806201
	Insulin Resistance	Improves (the measure goes down)		1 study	389 people
Studies that measured insulin resistance The effects of probiotics supplements on metabolic indices and clinical signs in patients with diabetic retinopathy, a randomized double blind clinical trial.J Diabetes Metab Disord · PMID 38932908
	Testosterone	Improves (the measure goes up)		1 study	47 people
Studies that measured testosterone Effects of probiotic supplementation on testosterone levels in healthy ageing men: A 12-week double-blind, placebo-controlled randomized clinical trial.Contemp Clin Trials Commun · PMID 38770015
	Total cholesterol	Improves (the measure goes down)		1 study	363 people
Studies that measured total cholesterol The effect of probiotic consumption on lipid profile, glycemic index, inflammatory markers, and liver function in NAFLD patients: A systematic review and meta-analysis of randomized controlled trials.J Diabetes Complications · PMID 38968867
	Blood Pressure	Improves (the measure goes down)			306 people
	Body Mass Index (BMI)	Improves (the measure goes down)			363 people
	Follicle-Stimulating Hormone	Improves (the measure goes up)			47 people
	High-density lipoprotein (HDL)	Improves (the measure goes up)			433 people
	Insulin	Changes; see studies			424 people
	Low-density lipoprotein (LDL)	Improves (the measure goes down)			433 people
	Luteinizing Hormone	Improves (the measure goes up)			47 people
	Sex Hormone Binding Globulin	Improves (the measure goes up)			47 people
	Thyroid-Stimulating Hormone	Improves (the measure goes up)			47 people
	Triglycerides	Improves (the measure goes down)			433 people

Menopause

Menopausal Symptoms: improves
Vaginal Dryness: improves

Menopause: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People
	Menopausal Symptoms Small Improvement	Improves (the measure goes down)	Small effect	1 study	462 people
Studies that measured menopausal symptoms Investigating the effects of probiotics during the menopause transition: A systematic review & meta-analysis.Clin Nutr ESPEN · PMID 40639456
	Vaginal Dryness	Improves (the measure goes up)			462 people

General Cardiovascular Health

Blood glucose: improves
HbA1c: improves
Insulin Resistance: improves

General Cardiovascular Health: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People
	Blood glucose Small Improvement	Improves (the measure goes down)	Small effect	1 study	450 people
Studies that measured blood glucose Effects of probiotics supplementation on glycemic profile in adults with type 2 diabetes mellitus: A grade-assessed systematic review and dose-response meta-analysis of randomized controlled trials.Clin Nutr ESPEN · PMID 39349104
	HbA1c	Improves (the measure goes down)		2 studies	671 people
Studies that measured hba1c The effects of probiotic supplementation on cardiometabolic health in patients with prediabetes: a systematic review, meta-analysis, and GRADE assessment.Front Nutr · 2025 · PMID 40959695 Probiotics Supplementation for Improving Glucolipid Parameters in Individuals with Prediabetes: A Systematic Review and Meta-Analysis of Randomized Trials.Probiotics Antimicrob Proteins · PMID 39806201
	Insulin Resistance	Improves (the measure goes down)		1 study	389 people
Studies that measured insulin resistance The effects of probiotics supplements on metabolic indices and clinical signs in patients with diabetic retinopathy, a randomized double blind clinical trial.J Diabetes Metab Disord · PMID 38932908
	Total cholesterol	Improves (the measure goes down)		1 study	363 people
Studies that measured total cholesterol The effect of probiotic consumption on lipid profile, glycemic index, inflammatory markers, and liver function in NAFLD patients: A systematic review and meta-analysis of randomized controlled trials.J Diabetes Complications · PMID 38968867
	Blood Pressure	Improves (the measure goes down)			306 people
	Body Mass Index (BMI)	Improves (the measure goes down)			363 people
	High-density lipoprotein (HDL)	Improves (the measure goes up)			433 people
	Insulin	Changes; see studies			424 people
	Low-density lipoprotein (LDL)	Improves (the measure goes down)			433 people
	Triglycerides	Improves (the measure goes down)			433 people

Irritable Bowel Syndrome (IBS)

Abdominal Pain: improves
Bloating: improves
Irritable Bowel Syndrome Symptoms: improves

Irritable Bowel Syndrome (IBS): outcomes studied for Probiotics
Outcome	Effect	Size	People
Abdominal Pain Moderate Improvement	Improves (the measure goes down)	Moderate effect	2,359 people
Bloating	Improves (the measure goes down)		702 people
Irritable Bowel Syndrome Symptoms	Improves (the measure goes down)		6,732 people
Quality of Life	Improves (the measure goes up)		732 people

Colorectal Cancer

Bloating
Diarrhea Symptoms: improves

Colorectal Cancer: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Bloating Mixed effect				344 people
	Diarrhea Symptoms	Improves (the measure goes down)		4 studies	408 people

Stress

Cognition
Sleep Quality: improves

Stress: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Cognition Mixed effect			4 studies	44 people
	Sleep Quality	Improves (the measure goes up)		1 study	55 people

Depression

Depression Symptoms: improves
Sleep Quality: improves
Sleep Duration: improves

Depression: outcomes studied for Probiotics
Outcome	Effect	Size	Studies	People
Depression Symptoms Small Improvement	Improves (the measure goes down)	Small effect	1 study	140 people
Sleep Quality	Improves (the measure goes up)		1 study	424 people
Sleep Duration	Improves (the measure goes up)			226 people
Sleep Efficiency	Improves (the measure goes up)			166 people
Sleep Latency	Improves (the measure goes down)			226 people

Insomnia

Depression Symptoms: improves
Sleep Quality: improves
Sleep Duration: improves

Insomnia: outcomes studied for Probiotics
Outcome	Effect	Size	Studies	People
Depression Symptoms Small Improvement	Improves (the measure goes down)	Small effect	1 study	140 people
Sleep Quality	Improves (the measure goes up)		1 study	424 people
Sleep Duration	Improves (the measure goes up)			226 people
Sleep Efficiency	Improves (the measure goes up)			166 people
Sleep Latency	Improves (the measure goes down)			226 people

Nonalcoholic Fatty Liver Disease (NAFLD)

Blood glucose: improves
HbA1c: improves
Insulin Resistance: improves

Nonalcoholic Fatty Liver Disease (NAFLD): outcomes studied for Probiotics
Outcome	Effect	Size	Studies	People
Blood glucose Small Improvement	Improves (the measure goes down)	Small effect	1 study	899 people
HbA1c	Improves (the measure goes down)		2 studies	899 people
Insulin Resistance	Improves (the measure goes down)		1 study	2,820 people
Total cholesterol	Improves (the measure goes down)		1 study	2,820 people
Body Mass Index (BMI)	Improves (the measure goes down)			1,921 people
High-density lipoprotein (HDL)	Improves (the measure goes up)			2,820 people
Insulin	Changes; see studies			899 people
Liver Enzymes	Changes; see studies			2,820 people
Liver Fat	Improves (the measure goes down)			1,921 people
Liver Fibrosis	Improves (the measure goes down)			1,921 people
Low-density lipoprotein (LDL)	Improves (the measure goes down)			2,820 people
TNF-Alpha	Improves (the measure goes down)			899 people
Triglycerides	Improves (the measure goes down)			2,820 people

Overweight

Body Fat: improves
Total cholesterol: improves
Weight: improves

Overweight: outcomes studied for Probiotics
Outcome	Effect	Size	Studies	People
Body Fat Small Decrease	Improves (the measure goes down)	Small effect	1 study	92 people
Total cholesterol	Improves (the measure goes down)		1 study	92 people
Weight	Improves (the measure goes down)		1 study	422 people
Body Mass Index (BMI)	Improves (the measure goes down)			244 people
High-density lipoprotein (HDL)	Improves (the measure goes up)			92 people
Hip Circumference	Improves (the measure goes down)			92 people
Low-density lipoprotein (LDL)	Improves (the measure goes down)			412 people
Muscle Mass	Improves (the measure goes up)			92 people
Visceral Fat	Improves (the measure goes down)			231 people
Waist circumference	Improves (the measure goes down)			297 people
Waist-Hip Ratio	Improves (the measure goes up)			92 people

Weight Loss & Maintenance

Body Fat: improves
Total cholesterol: improves
Weight: improves

Weight Loss & Maintenance: outcomes studied for Probiotics
Outcome	Effect	Size	Studies	People
Body Fat Small Decrease	Improves (the measure goes down)	Small effect	1 study	92 people
Total cholesterol	Improves (the measure goes down)		1 study	92 people
Weight	Improves (the measure goes down)		1 study	422 people
Body Mass Index (BMI)	Improves (the measure goes down)			244 people
High-density lipoprotein (HDL)	Improves (the measure goes up)			92 people
Hip Circumference	Improves (the measure goes down)			92 people
Low-density lipoprotein (LDL)	Improves (the measure goes down)			412 people
Muscle Mass	Improves (the measure goes up)			92 people
Visceral Fat	Improves (the measure goes down)			231 people
Waist circumference	Improves (the measure goes down)			297 people
Waist-Hip Ratio	Improves (the measure goes up)			92 people

Type 2 Diabetes

Blood glucose: improves
HbA1c: improves
Insulin Resistance: improves

Type 2 Diabetes: outcomes studied for Probiotics
Outcome	Effect	Size	Studies	People
Blood glucose Small Improvement	Improves (the measure goes down)	Small effect	1 study	1,920 people
HbA1c	Improves (the measure goes down)		2 studies	1,920 people
Insulin Resistance	Improves (the measure goes down)		1 study	1,920 people
Insulin	Changes; see studies			1,920 people

Body Composition

Body Fat: improves
Weight: improves
Body Mass Index (BMI): improves

Body Composition: outcomes studied for Probiotics
Outcome	Effect	Size	Studies	People
Body Fat Small Decrease	Improves (the measure goes down)	Small effect	1 study	92 people
Weight	Improves (the measure goes down)		1 study	92 people
Body Mass Index (BMI)	Improves (the measure goes down)			92 people
Hip Circumference	Improves (the measure goes down)			92 people
Low-density lipoprotein (LDL)	Improves (the measure goes down)			92 people
Muscle Mass	Improves (the measure goes up)			92 people
Waist circumference	Improves (the measure goes down)			92 people
Waist-Hip Ratio	Improves (the measure goes up)			92 people

Diabetic Retinopathy

Blood glucose: improves
C-Reactive Protein (CRP): improves
HbA1c: improves

Diabetic Retinopathy: outcomes studied for Probiotics
Outcome	Effect	Size	Studies	People
Blood glucose Small Improvement	Improves (the measure goes down)	Small effect	1 study	55 people
C-Reactive Protein (CRP)	Improves (the measure goes down)		2 studies	55 people
HbA1c	Improves (the measure goes down)		2 studies	55 people
Insulin Resistance	Improves (the measure goes down)		1 study	55 people
Diabetic Retinopathy Symptoms	Improves (the measure goes down)			55 people
Glutathione (GSH)	Improves (the measure goes up)			55 people
High-density lipoprotein (HDL)	Improves (the measure goes up)			55 people
Insulin	Changes; see studies			55 people
Low-density lipoprotein (LDL)	Improves (the measure goes down)			55 people
Total Antioxidant Capacity (TAC)	Improves (the measure goes up)			55 people

Hair Loss

Hair Regrowth
Microbiome: improves

Hair Loss: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Hair Regrowth No effect		NoneNo effect	2 studies	219 people
	Microbiome	Improves (the measure goes up)			115 people

Preeclampsia

All-Cause Mortality
Pre-Eclampsia Risk: changes; see studies

Preeclampsia: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People	Studies list
	All-Cause Mortality No effect		NoneNo effect	1 study	7,735 people
	Pre-Eclampsia Risk	Changes; see studies			7,735 people

Obesity

Body Mass Index (BMI)
Depression Symptoms: improves
Weight: improves

Obesity: outcomes studied for Probiotics
Outcome	Effect	Size	Studies	People
Body Mass Index (BMI) No effect		NoneNo effect		244 people
Depression Symptoms	Improves (the measure goes down)		1 study	488 people
Weight	Improves (the measure goes down)		1 study	422 people
Low-density lipoprotein (LDL)	Improves (the measure goes down)			412 people
Visceral Fat	Improves (the measure goes down)			231 people
Waist circumference	Improves (the measure goes down)			297 people

Cystic Fibrosis

Cystic Fibrosis Symptoms
Fecal Calprotectin: improves
Lung Function: improves

Cystic Fibrosis: outcomes studied for Probiotics
Outcome	Effect	Size	Studies	People
Cystic Fibrosis Symptoms No effect		NoneNo effect		258 people
Fecal Calprotectin	Improves (the measure goes up)		1 study	177 people
Lung Function	Improves (the measure goes up)		1 study	284 people
Quality of Life	Improves (the measure goes up)			37 people

Eczema (Atopic Dermatitis)

Allergic Disease Risk
Eczema Symptoms: improves

Eczema (Atopic Dermatitis): outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Allergic Disease Risk No effect		NoneNo effect		399 people
	Eczema Symptoms	Improves (the measure goes down)		1 study	440 people

Migraine Headache

Migraine Duration
Migraine Frequency: improves
Migraine Severity: improves

Migraine Headache: outcomes studied for Probiotics
Outcome	Effect	Size	People
Migraine Duration No effect		NoneNo effect	120 people
Migraine Frequency	Improves (the measure goes down)		120 people
Migraine Severity	Improves (the measure goes down)		120 people

Osteoarthritis (OA)

Body Mass Index (BMI)
C-Reactive Protein (CRP): improves
Osteoarthritis Symptoms: improves

Osteoarthritis (OA): outcomes studied for Probiotics
Outcome	Effect	Size	Studies	People
Body Mass Index (BMI) No effect		NoneNo effect		129 people
C-Reactive Protein (CRP)	Improves (the measure goes down)		2 studies	563 people
Osteoarthritis Symptoms	Improves (the measure goes down)		1 study	627 people
Pain	Improves (the measure goes down)			562 people

Hormone Health

Follicle-Stimulating Hormone
HbA1c: improves
Testosterone: improves

Hormone Health: outcomes studied for Probiotics
Outcome	Effect	Size	Studies	People
Follicle-Stimulating Hormone No effect		NoneNo effect		47 people
HbA1c	Improves (the measure goes down)		2 studies	47 people
Testosterone	Improves (the measure goes up)		1 study	47 people
Total cholesterol	Improves (the measure goes down)		1 study	47 people
High-density lipoprotein (HDL)	Improves (the measure goes up)			47 people
Low-density lipoprotein (LDL)	Improves (the measure goes down)			47 people
Luteinizing Hormone	Improves (the measure goes up)			47 people
Sex Hormone Binding Globulin	Improves (the measure goes up)			47 people
Thyroid-Stimulating Hormone	Improves (the measure goes up)			47 people
Triglycerides	Improves (the measure goes down)			47 people

Metabolic Syndrome

Body Mass Index (BMI)
Weight: improves
Low-density lipoprotein (LDL): improves

Metabolic Syndrome: outcomes studied for Probiotics
Outcome	Effect	Size	Studies	People
Body Mass Index (BMI) No effect		NoneNo effect		244 people
Weight	Improves (the measure goes down)		1 study	422 people
Low-density lipoprotein (LDL)	Improves (the measure goes down)			412 people
Visceral Fat	Improves (the measure goes down)			231 people
Waist circumference	Improves (the measure goes down)			297 people

Mild Cognitive Impairment (MCI)

Attention
Cognition: improves
Memory: improves

Mild Cognitive Impairment (MCI): outcomes studied for Probiotics
Outcome	Effect	Size	Studies	People
Attention No effect		NoneNo effect		402 people
Cognition	Improves (the measure goes up)		4 studies	419 people
Memory	Improves (the measure goes up)			517 people

Prediabetes

Beta-cell function
HbA1c: improves
Blood glucose: improves

Prediabetes: outcomes studied for Probiotics
Outcome	Effect	Size	Studies	People
Beta-cell function No effect		NoneNo effect		153 people
HbA1c	Improves (the measure goes down)		2 studies	567 people
Blood glucose	Improves (the measure goes down)		1 study	576 people
Insulin Resistance	Improves (the measure goes down)		1 study	515 people
Total cholesterol	Improves (the measure goes down)		1 study	253 people
Blood Pressure	Improves (the measure goes down)			432 people
High-density lipoprotein (HDL)	Improves (the measure goes up)			323 people
Insulin	Changes; see studies			550 people
Low-density lipoprotein (LDL)	Improves (the measure goes down)			323 people
Triglycerides	Improves (the measure goes down)			323 people

Food Allergy

Allergic Disease Risk
Eczema Symptoms: improves

Food Allergy: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Allergic Disease Risk No effect		NoneNo effect		399 people
	Eczema Symptoms	Improves (the measure goes down)		1 study	440 people

Malnutrition

Height
Weight: changes; see studies
Lower Respiratory Tract Infection Risk: changes; see studies

Malnutrition: outcomes studied for Probiotics
Outcome	Effect	Size	Studies	People
Height No effect		NoneNo effect		530 people
Weight	Changes; see studies		1 study	562 people
Lower Respiratory Tract Infection Risk	Changes; see studies			3,086 people

Alzheimer’s Disease

Attention
Cognition: improves
Memory: improves

Alzheimer’s Disease: outcomes studied for Probiotics
Outcome	Effect	Size	Studies	People
Attention No effect		NoneNo effect		402 people
Cognition	Improves (the measure goes up)		4 studies	419 people
Memory	Improves (the measure goes up)			517 people

Autism Spectrum Disorder (ASD)

Autism Symptoms: improves

Autism Spectrum Disorder (ASD): outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Autism Symptoms	Improves (the measure goes down)		3 studies	480 people

Head and Neck Cancer

Mucositis Symptoms: improves

Head and Neck Cancer: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Mucositis Symptoms	Improves (the measure goes down)		2 studies	691 people

Schizophrenia

C-Reactive Protein (CRP): improves

Schizophrenia: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People	Studies list
	C-Reactive Protein (CRP)	Improves (the measure goes down)		2 studies	239 people

Radiation Therapy Side-Effects

Mucositis Symptoms: improves

Radiation Therapy Side-Effects: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Mucositis Symptoms	Improves (the measure goes down)		2 studies	1,055 people

Bacterial Vaginosis (BV)

Bacterial Vaginosis Symptoms: improves

Bacterial Vaginosis (BV): outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Bacterial Vaginosis Symptoms	Improves (the measure goes down)		1 study	1,662 people

Bone Health

Bone Mineral Density: improves

Bone Health: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Bone Mineral Density	Improves (the measure goes up)		1 study	479 people

Cognitive Improvement

Serum BDNF: improves

Cognitive Improvement: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Serum BDNF	Improves (the measure goes up)		1 study	2,372 people

Pregnancy and Delivery Health

Gestational Diabetes Risk: changes; see studies

Pregnancy and Delivery Health: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Gestational Diabetes Risk	Changes; see studies		1 study	3,527 people

Vaginal Health

Vaginal Infection Risk: changes; see studies

Vaginal Health: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Vaginal Infection Risk	Changes; see studies		1 study	100 people

Gingivitis

Dental Health Metrics: improves

Gingivitis: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Dental Health Metrics	Improves (the measure goes up)		1 study	951 people

Periodontitis

Dental Health Metrics: improves

Periodontitis: outcomes studied for Probiotics
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Dental Health Metrics	Improves (the measure goes up)		1 study	951 people

What the published studies found

9 automated readings

Automated reading of the published studies (Decosa evidence engine), for outcomes Dr. Grey has not graded yet. It is not a Dr. Grey grade and does not change one. How it is read

LDL cholesterol
The best available review (2026, 28 studies) found an improvement in LDL cholesterol. That review studied individuals with overweight and obesity. 6 of the 8 studies read agree; 2 found no clear difference. The evidence is moderate.
8 studies counted of 8 read: 7 reviews and 1 trial (50 people in the trials).
1. Meta-analysis, 2026; 28 studies; individuals with overweight and obesity: improves (the review the verdict rests on). LDL (MD = -0.06 mmol/L; 95% CI: -0.12, -0.01) Effect of Probiotic and Symbiotic Supplementation on Lipid Parameters in Individuals With Overweight and Obesity: A Systematic Review and Meta-AnalysisPubMed 42130343
2. Meta-analysis, 2024; 11 studies; overweight or obese women: improves. Impact of probiotics on weight loss, glucose and lipid metabolism in overweight or obese women: A meta-analysis of randomized controlled trialsPubMed 39114432
3. Meta-analysis, 2023; 40 studies, 2,795 people; patients with cardiometabolic risk factors: improves. The effect of probiotic and synbiotic supplementation on lipid parameters among patients with cardiometabolic risk factors: a systematic review and meta-analysis of clinical trialsPubMed 35934838
4. Meta-analysis, 2021; 39 studies, 2,237 people: improves. reductions in blood low-density lipoprotein cholesterol (LDL-C) The effect of probiotic fermented milk products on blood lipid concentrations: A systematic review and meta-analysis of randomized controlled trialsPubMed 33612379
5. Meta-analysis, 2018; 10 studies; pregnant women, including those with gestational diabetes mellitus: no clear difference. low density lipoprotein cholesterol (LDL-c) (OR -0.38 The effects of probiotics supplementation on metabolic health in pregnant women: An evidence based meta-analysisPubMed 29782556
6. Meta-analysis, 2017; 15 studies, 976 people: improves. Effect of probiotic Lactobacillus on lipid profile: A systematic review and meta-analysis of randomized, controlled trialsPubMed 28594860
7. Meta-analysis, 2015; 15 studies, 788 people: improves. Effects of probiotics consumption on lowering lipids and CVD risk factors: a systematic review and meta-analysis of randomized controlled trialsPubMed 26340330
8. Randomised trial, 2026; 50 people; women with polycystic ovary syndrome: no clear difference. No statistically significant between-group differences were detected More than Hormones? Metabolic Effects of Twelve-Week Probiotic Supplementation in Women with Polycystic Ovary Syndrome: A Secondary Analysis of a Randomized Double-Blind Placebo-Controlled StudyPubMed 42797074
Automated reading of the published studies (Decosa evidence engine), run 30 Sep 2026. It reads abstracts, can miss studies, and a repeat run can differ.
Bloating
The best available review (2013, 37 studies) found an improvement in bloating. That review studied adults with lower gastrointestinal symptoms. 5 of the 7 studies read agree; 2 found no clear difference. The evidence is moderate.
Side effects: 1 of the 8 studies that reported on them found more with Probiotics (gastrointestinal adverse events).
7 studies counted of 11 read: 4 reviews and 3 trials (500 people in the trials).
1. Systematic review, 2013; 37 studies; adults with lower gastrointestinal symptoms: improves (the review the verdict rests on). reduce bloating/distension and improve bowel movement frequency/consistency in some IBS patients Systematic review: probiotics in the management of lower gastrointestinal symptoms in clinical practice -- an evidence-based international guidePubMed 23981066
2. Systematic review, 2026; patients with irritable bowel syndrome: improves. probiotics can modestly improve global symptoms, abdominal pain, and bloating in IBS Clinical guidance and practical recommendations for probiotic use in patients with irritable bowel syndrome, functional constipation, and Clostridioides difficile infection considering sex-based differences: a Korean translationPubMed 41980747
3. Meta-analysis, 2024; 23 studies, 3,288 people: improves. Efficacy of Probiotics in the Management of Irritable Bowel Syndrome: A Systematic Review and Meta-AnalysisPubMed 39830577
4. Meta-analysis, 2022; 13 studies; healthy adults: no clear difference. No improvement in abdominal pain and bloating was found. Effects of Bifidobacterium animalis subspecies lactis supplementation on gastrointestinal symptoms: systematic review with meta-analysisPubMed 34918142
5. Randomised trial, 2026; 350 people; healthy individuals with self-reported bloating or indigestion: improves. Bloating and gas were reduced in the synbiotic arm A Randomized, Placebo-Controlled Trial Evaluating Multi-Species Synbiotic Supplementation for Bloating, Gas, and Abdominal DiscomfortPubMed 41599868
6. Crossover trial, 2026; 25 people; healthy adults: no clear difference. A high-fibre snack containing Lacticaseibacillus rhamnosus GG for healthy adults: a randomised, double-blind, placebo-controlled crossover trialPubMed 42642033
7. Randomised trial, 2023; 125 people; patients with functional abdominal bloating: improves. patients in the probiotic group had a significantly lower frequency of abdominal bloating Evaluation and comparison of therapeutic effects of probiotics and colloidal bismuth subcitrate on abdominal bloatingPubMed 37520877
Automated reading of the published studies (Decosa evidence engine), run 30 Sep 2026. It reads abstracts, can miss studies, and a repeat run can differ.
Blood pressure
The studies disagree. A Cochrane review (2025, 17 studies, 838 people) did not settle it for blood pressure, while 7 of the 10 studies read found an improvement. The evidence is very weak.
10 studies counted of 10 read: 10 reviews.
1. Systematic review, 2025; 17 studies, 838 people; children and adolescents with overweight or obesity: unclear: evidence too weak to tell (the review the verdict rests on). Probiotics compared to placebo may have little to no effect on Gut microbiome-based interventions for the management of obesity in children and adolescents aged up to 19 yearsPubMed 40637175
2. Meta-analysis, 2026; 17 studies, 1,281 people; adults with prediabetes and type 2 diabetes mellitus: improves. significantly reduction in both systolic BP Effects of Probiotics and Synbiotics Supplementation on Blood Pressure in Adults with Prediabetes and Type 2 Diabetes Mellitus: A Grade-Assessed Systematic Review and Dose-Response Meta-AnalysisPubMed 40815364
3. Meta-analysis, 2025; 26 studies, 1,755 people; overweight and obese adults: improves. beneficial effect on systolic blood pressure The Effects of Probiotics Consumption on Blood Pressure, Lipid Profile, Glycemic Indices, and Inflammatory Parameters in Overweight and Obese Adults: A Systematic Review and Meta-Analysis of Randomized Controlled TrialsPubMed 40735396
4. Systematic review, 2022; 5 studies, 250 people; solid organ transplant recipients: unclear: evidence too weak to tell. Probiotics had uncertain effects on GI side effects, infection rates immediately post-transplant, liver function, blood … Synbiotics, prebiotics and probiotics for solid organ transplant recipientsPubMed 36126902
5. Systematic review, 2020; 5 studies, 2,703 people; hypertensive adults with or without type 2 diabetes: improves. moderate effect of probiotics on BP in hypertensive adults Effect of probiotic foods and supplements on blood pressure: a systematic review of meta-analyses studies of controlled trialsPubMed 32550214
6. Meta-analysis, 2020; 14 studies, 846 people; patients with hypertension: improves. significant reduction in SBP by - 2.05 mmHg Effects of Probiotics on Patients with Hypertension: a Systematic Review and Meta-AnalysisPubMed 32200440
7. Meta-analysis, 2020; 7 studies, 653 people: no clear difference. Effect of Lactobacillusplantarum containing probiotics on blood pressure: A systematic review and meta-analysisPubMed 31987993
8. Meta-analysis, 2020; 32 studies; patients with type 2 diabetes mellitus: improves. significant effect of probiotics on reducing Probiotics have beneficial metabolic effects in patients with type 2 diabetes mellitus: a meta-analysis of randomized clinical trialsPubMed 32678128
9. Meta-analysis, 2018; 11 studies, 641 people; adults with type II diabetes: improves. significantly decreased SBP (WMD, -3.28 mmHg Probiotic supplementation for management of cardiovascular risk factors in adults with type II diabetes: A systematic review and meta-analysisPubMed 28318686
10. Meta-analysis, 2014; 9 studies: improves. significantly changed systolic BP by -3.56 mm Hg Effect of probiotics on blood pressure: a systematic review and meta-analysis of randomized, controlled trialsPubMed 25047574
Automated reading of the published studies (Decosa evidence engine), run 30 Sep 2026. It reads abstracts, can miss studies, and a repeat run can differ.
Gastrointestinal symptoms
The studies disagree. A Cochrane review (2022, 5 studies, 250 people) did not settle it for gastrointestinal symptoms, while 8 of the 10 studies read found an improvement. The evidence is very weak.
10 studies counted of 11 read: 6 reviews and 4 trials (161 people in the trials).
1. Systematic review, 2022; 5 studies, 250 people; solid organ transplant recipients: unclear: evidence too weak to tell (the review the verdict rests on). Probiotics had uncertain effects on GI side effects Synbiotics, prebiotics and probiotics for solid organ transplant recipientsPubMed 36126902
2. Systematic review, 2026; 15 studies, 1,015 people; individuals with autism spectrum disorder: improves. improvements in GI symptoms, such as reduced abdominal pain Pre- and probiotics for gastrointestinal and behavioral symptoms in autism spectrum disorder: a systematic reviewPubMed 42682264
3. Meta-analysis, 2026; 28 studies; patients with Helicobacter pylori infection: improves. Evaluating probiotic monotherapy in Helicobacter pylori infection: A meta-analysis of randomized controlled trials with trial sequential analysisPubMed 41581709
4. Meta-analysis, 2026; 12 studies; adults with colorectal cancer receiving chemotherapy: improves. significantly reduced chemotherapy-related diarrhea (odds ratio 0.48 Comparative Effects of Microbiota-Modifying Interventions for Gastrointestinal Disorders in Adults with Colorectal Cancer: A Systematic Review and Network Meta-AnalysisPubMed 42804968
5. Meta-analysis, 2025; 18 studies, 1,246 people: improves. alleviated gastrointestinal disturbances, such as diarrhea Research progress of probiotics intervention on reconstruction of intestinal flora and improvement of quality of life in patients after endometrial cancer surgeryPubMed 41050754
6. Meta-analysis, 2015; 23 studies, 3,938 people; children receiving antibiotics: improves. incidence of AAD in the probiotic group was 8% Probiotics for the prevention of pediatric antibiotic-associated diarrheaPubMed 26695080
7. Randomised trial, 2025; 59 people; overweight and obese adults aged 20-40: improves. alleviated symptoms such as gastroesophageal reflux Impact of probiotic Lactobacillus plantarum GKM3 on gastrointestinal health in overweight and obese individuals: A randomized clinical trialPubMed 40383259
8. Randomised trial, 2025; 22 people; patients with irritable bowel syndrome with predominant diarrhea: improves. Colonoscopic administration of probiotics to treat irritable bowel syndrome with predominant diarrhea: a randomized placebo-controlled clinical trialPubMed 39849073
9. Randomised trial, 2025; 16 people; female dancers: no clear difference. No improvement in gastrointestinal symptoms was observed A Randomized Controlled Trial Evaluating the Effects of a Probiotic Containing Lactobacillus helveticus R0052 and Bifidobacterium longum R0175 on Gastrointestinal Symptoms and Metabolomic Profiles in Female DancersPubMed 40565286
10. Randomised trial, 2017; 64 people; patients receiving aspirin for more than one month: improves. FSSG and GSRS scores were also significantly improved Yogurt Containing Lactobacillus gasseri Mitigates Aspirin-Induced Small Bowel Injuries: A Prospective, Randomized, Double-Blind, Placebo-Controlled TrialPubMed 28052291
Automated reading of the published studies (Decosa evidence engine), run 30 Sep 2026. It reads abstracts, can miss studies, and a repeat run can differ.
Irritable bowel syndrome symptoms
A Cochrane review (2023, 18 studies, 1,309 people) found a large improvement in irritable bowel syndrome symptoms. That review studied children with functional abdominal pain disorders. 9 of the 11 studies read agree; 1 found no clear answer, 1 found no clear difference. The evidence is limited.
11 studies counted of 11 read: 11 reviews.
1. Meta-analysis, 2023; 18 studies, 1,309 people; children with functional abdominal pain disorders: improves (the review the verdict rests on). Probiotics may achieve more treatment success when compared with placebo Probiotics for management of functional abdominal pain disorders in childrenPubMed 36799531
2. Meta-analysis, 2026; 12 studies, 1,303 people; patients with irritable bowel syndrome: improves. Multistrain probiotics significantly reduced total IBS-SSS scores [mean difference = -43.66, 95% confidence interval (CI): … Effect of multistrain probiotics on symptom severity in irritable bowel syndrome: a systematic review and meta-analysis of irritable bowel syndrome-symptom severity score outcomesPubMed 41433106
3. Meta-analysis, 2025; 16 studies, 2,823 people: improves. Probiotics showed a clinically significant overall improvement Efficacy of Specific Probiotic Strains in Subtypes of Irritable Bowel Syndrome: Systematic Review and Meta-Analysis of Randomized Controlled TrialsPubMed 41597375
4. Systematic review, 2025; 44 studies; patients with irritable bowel syndrome: improves. significantly lower effectiveness than the probiotics group Effects of Probiotics and Diet Management in Patients With Irritable Bowel Syndrome: A Systematic Review and Network Meta-analysisPubMed 39862384
5. Meta-analysis, 2024; 23 studies, 3,288 people: improves. Efficacy of Probiotics in the Management of Irritable Bowel Syndrome: A Systematic Review and Meta-AnalysisPubMed 39830577
6. Meta-analysis, 2024; 20 studies, 3,011 people: improves. probiotics are more effective than placebo in reducing global IBS symptoms improvement rate Efficacy and safety of probiotics in irritable bowel syndrome: A systematic review and meta-analysisPubMed 38479936
7. Meta-analysis, 2023; 72 studies; people with irritable bowel syndrome: improves. significantly better overall effect of probiotics than placebo Probiotics for the management of irritable bowel syndrome: a systematic review and three-level meta-analysisPubMed 37565634
8. Meta-analysis, 2022; 16 studies, 1,585 people; patients with diarrhea: improves. Meta-analysis of the efficacy of probiotics to treat diarrheaPubMed 36197181
9. Meta-analysis, 2018; 53 studies, 5,545 people; adults with irritable bowel syndrome: unclear: evidence too weak to tell. beneficial effects on global IBS symptoms and abdominal pain Systematic review with meta-analysis: the efficacy of prebiotics, probiotics, synbiotics and antibiotics in irritable bowel syndromePubMed 30294792
10. Meta-analysis, 2017; 19 studies, 1,453 people; children with recurrent abdominal pain or irritable bowel syndrome: improves. probiotics were more likely to experience improvement in pain Dietary interventions for recurrent abdominal pain in childhoodPubMed 28334433
11. Systematic review, 2009; 2 studies, 168 people; school-age children with recurrent abdominal pain: no clear difference. Dietary interventions for recurrent abdominal pain (RAP) and irritable bowel syndrome (IBS) in childhoodPubMed 19160214
Automated reading of the published studies (Decosa evidence engine), run 30 Sep 2026. It reads abstracts, can miss studies, and a repeat run can differ.
Memory
The best available review (2026, 21 studies) found an improvement in memory. That review studied people across the human lifespan. 6 of the 8 studies read agree; 1 found no clear answer, 1 found no clear difference. The evidence is moderate.
8 studies counted of 9 read: 5 reviews and 3 trials (242 people in the trials).
1. Meta-analysis, 2026; 21 studies; people across the human lifespan: improves (the review the verdict rests on). Effects of probiotics on cognitive function across the human lifespan: a meta-analysisPubMed 40983638
2. Systematic review, 2025; 39 studies; animal models and humans: unclear: evidence too weak to tell. consistently improved spatial learning, working memory Early-life cognitive effects of prebiotics and probiotics: A cross-species systematic reviewPubMed 40886953
3. Meta-analysis, 2024; 12 studies, 852 people; adults with mild cognitive impairment or Alzheimer's disease: improves. recall/delayed memory (SMD=0.67; 95% CI: 0.32, 1.02) Effect of probiotics on cognitive function in adults with mild cognitive impairment or Alzheimer's disease: A meta-analysis of randomized controlled trialsPubMed 38641508
4. Meta-analysis, 2023; 10 studies, 702 people; older adults with cognitive impairment: improves. Evaluation of improvement of cognitive impairment in older adults with probiotic supplementation: A systematic review and meta-analysisPubMed 37788563
5. Systematic review, 2016; 38 studies; animals and humans: improves. Effect of Probiotics on Central Nervous System Functions in Animals and Humans: A Systematic ReviewPubMed 27413138
6. Randomised trial, 2022; 59 people; healthy young adults: no clear difference. There were no effects on cognitive performance or mental health. Evidence in favor of the … Effects of a multi-strain probiotic on hippocampal structure and function, cognition, and emotional well-being in healthy individuals: a double-blind randomised-controlled trialPubMed 35513910
7. Randomised trial, 2020; 80 people; older adults with suspected mild cognitive impairment: improves. significant improvement in domain scores of immediate memory Probiotic Bifidobacterium breve in Improving Cognitive Functions of Older Adults with Suspected Mild Cognitive Impairment: A Randomized, Double-Blind, Placebo-Controlled TrialPubMed 32623402
8. Randomised trial, 2019; 103 people; stressed adults with moderate stress: improves. enhanced memory and cognitive traits such as social emotional cognition Probiotic Lactobacillus plantarum P8 alleviated stress and anxiety while enhancing memory and cognition in stressed adults: A randomised, double-blind, placebo-controlled studyPubMed 30266270
Automated reading of the published studies (Decosa evidence engine), run 30 Sep 2026. It reads abstracts, can miss studies, and a repeat run can differ.
Respiratory infections
A Cochrane review (2022, 24 studies, 6,950 people) found a small improvement in respiratory infections. That review studied people of all ages at risk of acute URTIs. 6 of the 7 studies read agree; 1 found no clear answer. The evidence is limited.
7 studies counted of 10 read: 6 reviews and 1 trial (120 people in the trials).
1. Systematic review, 2022; 24 studies, 6,950 people; people of all ages at risk of acute URTIs: improves (the review the verdict rests on). probiotics may reduce the number of participants diagnosed with URTIs Probiotics for preventing acute upper respiratory tract infectionsPubMed 36001877
2. Systematic review, 2026; 8 studies, 1,158 people; children with respiratory tract infections: improves. Comparative efficacy and safety of probiotic for respiratory tract infections in children: a network meta-analysisPubMed 42602161
3. Meta-analysis, 2026; 32 studies; patients with upper respiratory tract infections: unclear: evidence too weak to tell. pooled incidence reduction was non-significant (RD = -0.07 The Efficacy of Probiotics in Treating Upper Respiratory Tract Infections, Allergic Rhinitis, and Chronic Rhinosinusitis: A Systematic Review and Meta-AnalysisPubMed 42197372
4. Meta-analysis, 2025; 13 studies; patients with respiratory diseases: improves. significantly reduced the incidence of respiratory disease episodes Role of Lacticaseibacillus rhamnosus GG in the Management of Respiratory Diseases: A Systematic Review and Meta-AnalysisPubMed 40612762
5. Meta-analysis, 2019; 17 studies, 3,488 people; children aged up to 18 years: improves. Probiotics for preventing acute otitis media in childrenPubMed 31210358
6. Meta-analysis, 2014; 8 studies, 1,083 people; ICU patients receiving mechanical ventilation: improves. use of probiotics decreased the incidence of VAP Probiotics for preventing ventilator-associated pneumoniaPubMed 25344083
7. Randomised trial, 2026; 120 people; children with recurrent respiratory tract infections: improves. Probiotics significantly improved clinical efficacy compared with placebo Probiotic modulation of gut microbiota with Bifidobacterium animalis subsp. lactis XLTG11 and Lactobacillus plantarum CCFM8661 mitigates recurrent respiratory infections in children: a randomised-controlled trialPubMed 42090020
Automated reading of the published studies (Decosa evidence engine), run 30 Sep 2026. It reads abstracts, can miss studies, and a repeat run can differ.
Sleep quality
The best available review (2025, 6 studies, 424 people) found an improvement in sleep quality. That review studied patients with insomnia. 7 of the 8 studies read agree; 1 found no clear answer. The evidence is moderate.
8 studies counted of 11 read: 7 reviews and 1 trial.
1. Systematic review, 2025; 6 studies, 424 people; patients with insomnia: improves (the review the verdict rests on). significant reduction in Pittsburgh Sleep Quality Index (PSQI) Impact of probiotics on sleep quality and mood states in patients with insomnia: a systematic review and meta-analysisPubMed 40740336
2. Systematic review, 2026; 13 studies, 890 people; adults, healthy and poor sleep quality: improves. probiotic supplementation significantly reduced PSQI scores Association between probiotic intervention and sleep quality in the general adult population: a systematic review and meta-analysisPubMed 41958906
3. Systematic review, 2026; 19 studies, 762 people: improves. Overall, probiotic intake appears to modify resting state connectivity and activity, decrease involvement of several … The effects of oral probiotic intervention on brain structure and function in human adults: a systematic reviewPubMed 41501074
4. Meta-analysis, 2024; 15 studies: improves. PSQI) scores in the probiotics group was significantly lower Effects of probiotics on sleep parameters: A systematic review and meta-analysisPubMed 39094854
5. Systematic review, 2024; 11 studies; adults with sleep disorders or sub-healthy sleep conditions: improves. improves sleep states to some extent Effect of probiotics and paraprobiotics on patients with sleep disorders and sub-healthy sleep conditions: a meta-analysis of randomized controlled trialsPubMed 39479010
6. Meta-analysis, 2023; 18 studies: unclear: evidence too weak to tell. not demonstrated to be associated with significant improvement in sleep quality Effect of gut microbiota modulation on sleep: a systematic review and meta-analysis of clinical trialsPubMed 37023468
7. Meta-analysis, 2023; people with sleep disturbances: improves. probiotics supplementation significantly reduced the self-assessed parameter Microbiota Composition and Probiotics Supplementations on Sleep Quality-A Systematic Review and Meta-AnalysisPubMed 38131749
8. Randomised trial, 2024; healthy adults under mild stress aged 18-35 years: improves. exhibited significant improvements in wearable device- measured sleep duration Lacticaseibacillus paracasei 207-27 alters the microbiota-gut-brain axis to improve wearable device-measured sleep duration in healthy adults: a randomized, double-blind, placebo-controlled trialPubMed 39385735
Automated reading of the published studies (Decosa evidence engine), run 30 Sep 2026. It reads abstracts, can miss studies, and a repeat run can differ.
Stress
The best available review (2026, 12 studies, 3,350 people) found a small improvement in stress. That review studied healthy working adults. All 4 studies read agree. The evidence is moderate.
4 studies counted of 11 read: 3 reviews and 1 trial (75 people in the trials).
1. Meta-analysis, 2026; 12 studies, 3,350 people; healthy working adults: improves (the review the verdict rests on). statistically significant positive effect on subclinical psychological outcomes Probiotic intake and mental health in healthy working adults: a systematic review and meta-analysis of randomized controlled trialsPubMed 41501907
2. Systematic review, 2026; 6 studies, 180 people; exercised individuals and athletes: improves. occasional reductions in stress, anxiety, and fatigue The effect of probiotic and synbiotic supplementation on sleep parameters in exercised population: a systematic review and synthesis without meta-analysis (SWiM) of randomized controlled trialsPubMed 42184272
3. Meta-analysis, 2020; 11 studies, 577 people: improves. probiotic supplementation increased total antioxidant capacity (TAC) The Effects of Supplementation with Probiotic on Biomarkers of Oxidative Stress in Adult Subjects: a Systematic Review and Meta-analysis of Randomized TrialsPubMed 30666617
4. Randomised trial, 2026; 75 people; healthy older adults aged 55-70: improves. showing a significant between-group advantage over the placebo Pediococcus acidilactici PA53 Improves Emotional Well-Being and Gut Health While Modulating Microbiota Composition in Older Adults: A Randomized, Double-Blind, Placebo-Controlled TrialPubMed 42235825
Automated reading of the published studies (Decosa evidence engine), run 30 Sep 2026. It reads abstracts, can miss studies, and a repeat run can differ.

Key findings

AppetiteChemotherapy Side EffectsWorsens (the measure goes up)
Abdominal PainImproves (the measure goes down)
Cognition

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Studies cited

59 studies from PubMed

The effects of probiotic supplementation on cardiometabolic health in patients with prediabetes: a systematic review, meta-analysis, and GRADE assessment.Front Nutr, 2025 · PMID 40959695
Lactococcus lactis strain Plasma activates plasmacytoid dendritic cells and mitigates common cold-like symptoms in healthy adults: a meta-analysis of individual participant data.Front Immunol, 2025 · PMID 41280892
Probiotics and Immune Health: Current Knowledge and Future PerspectivesFront Immunol, 2022 · PMID 35367345
Probiotics for Irritable Bowel Syndrome: A Systematic Review and Meta-AnalysisNutrients, 2022 · PMID 35185242
Probiotics for Prevention and Treatment of Diarrhea: A Systematic Review and Meta-AnalysisJ Clin Gastroenterol, 2021 · PMID 34065205
Probiotics for the Prevention and Treatment of Depression: A Systematic Review and Meta-AnalysisClin Nutr, 2021 · PMID 33572797
Effects of Probiotics on Metabolic Syndrome: A Systematic Review of Randomized Clinical TrialsNutrients, 2021 · PMID 34205166
Probiotics and Weight Loss: A Systematic Review and Meta-AnalysisObes Rev, 2021 · PMID 33578617
The Gut Microbiome, Probiotics, and Their Impact on Skin Health: A ReviewInt J Mol Sci, 2021 · PMID 34296427
Health Benefits of Probiotics: A ReviewISRN Nutr, 2020 · PMID 32110829
Probiotics: Comprehensive Review of Growth Promotion Mechanisms and Action in Food ProductsFront Microbiol, 2020 · PMID 33189627
Probiotics: Classification, Mode of Action and Role in Human NutritionPostepy Hig Med Dosw, 2020 · PMID 32754318
Safety of Probiotics: A Comprehensive ReviewClin Infect Dis, 2019 · PMID 31256138
Probiotics, Prebiotics and Inflammation: A Review of the ScienceBenef Microbes, 2019 · PMID 31787341
Probiotics and Healthy Ageing: A Systematic Review and Meta-AnalysisMaturitas, 2019 · PMID 30796467
World Gastroenterology Organisation Global Guidelines: Probiotics and PrebioticsJ Clin Gastroenterol, 2017 · PMID 30954979
Probiotics for Human Use: Current Advances and Future PerspectivesNat Rev Gastroenterol Hepatol, 2017 · PMID 28639578
Probiotics for people with cystic fibrosis.Cochrane Database Syst Rev · PMID 31962375
Probiotics for the prevention of gestational diabetes mellitus: A meta-analysis of randomized controlled trials.Biomol Biomed · PMID 38642385
The effects of probiotics supplements on metabolic indices and clinical signs in patients with diabetic retinopathy, a randomized double blind clinical trial.J Diabetes Metab Disord · PMID 38932908
Effect of applying Lactiplantibacillus plantarum subsp. plantarum N793 to the scalps of men and women with thinning hair: a randomized, double-blind, placebo-controlled, parallel-group study.Biosci Microbiota Food Health · PMID 38966052
Randomized Clinical Trial to Evaluate the Effect of Probiotic Intake on Androgenic Alopecia.Nutrients · PMID 39275216
Impact of probiotics on sleep quality and mood states in patients with insomnia: a systematic review and meta-analysis.Front Microbiol · PMID 40740336
Gaba-producing lactobacilli boost cognitive reactivity to negative mood without improving cognitive performance: A human Double-Blind Placebo-Controlled Cross-Over study.Brain Behav Immun · PMID 39163908
The effect of probiotic consumption on lipid profile, glycemic index, inflammatory markers, and liver function in NAFLD patients: A systematic review and meta-analysis of randomized controlled trials.J Diabetes Complications · PMID 38968867
Efficacy of probiotics in the treatment of oral mucositis in head and neck cancer patients: A systematic review and meta-analysis.Microb Pathog · PMID 38971507
The effect of probiotics on severe oral mucositis in cancer patients undergoing chemotherapy and/or radiotherapy: A meta-analysis.J Stomatol Oral Maxillofac Surg · PMID 39187039
Oral probiotic supplementation to alleviate diarrhea induced by fluoropyrimidines or irinotecan-based chemotherapy: A systematic review and meta-analysis.Complement Ther Med · PMID 39993479
The impact of probiotics on core autism symptoms - A systematic review and meta-analysis of randomized clinical trials.Clin Nutr ESPEN · PMID 39173907
Efficacy and safety of Bacteroides fragilis BF839 for pediatric autism spectrum disorder: a randomized clinical trial.Front Nutr · PMID 39290561
Probiotics for autism spectrum disorder: An updated systematic review and meta-analysis of effects on symptoms.J Psychiatr Res · PMID 39265200
The efficacy and safety of probiotics in the adjuvant treatment of psoriasis: a systematic review and meta-analysis of randomized controlled trials.Front Med · PMID 39328313
Effects of probiotic supplementation on testosterone levels in healthy ageing men: A 12-week double-blind, placebo-controlled randomized clinical trial.Contemp Clin Trials Commun · PMID 38770015
A 12-Week, Single-Centre, Randomised, Double-Blind, Placebo-Controlled, Parallel-Design Clinical Trial for the Evaluation of the Efficacy and Safety of Lactiplantibacillus plantarum SKO-001 in Reducing Body Fat.Nutrients · PMID 38674828
Effects of oral supplementation of probiotics on body weight and visceral fat in obese patients: a meta-analysis and systematic review.Sci Rep · PMID 39984625
The effects of probiotics administration during pregnancy on preeclampsia and associated maternal, fetal, and newborn outcomes: a systematic review and meta-analysis.Am J Obstet Gynecol MFM · PMID 38447676
Effects of probiotics supplementation on glycemic profile in adults with type 2 diabetes mellitus: A grade-assessed systematic review and dose-response meta-analysis of randomized controlled trials.Clin Nutr ESPEN · PMID 39349104
The Effect of Probiotics on Obesity with Comorbid Depression: A Systematic Review and Meta-Analysis.Br J Hosp Med · PMID 39347684
A network meta-analysis of probiotics in the treatment of childhood asthma.Front Pediatr · PMID 41098501
Efficacy of probiotics as adjuvant therapy in bronchial asthma: a systematic review and meta-analysis.Allergy Asthma Clin Immunol · PMID 39563347
Efficacy and safety of Saccharomyces boulardii as an adjuvant therapy for the eradication of Helicobacter pylori: a meta-analysis.Front Cell Infect Microbiol · PMID 40012609
Efficacy of probiotics regimens for Helicobacter pylori eradication: A systematic review, pairwise, and network meta-analysis of randomized controlled trials.Clin Nutr ESPEN · PMID 39642994
Effect of probiotics on C-reactive protein levels in schizophrenia: Evidence from a systematic review and meta-analysis.Complement Ther Med · PMID 39798817
Probiotics Supplementation for Improving Glucolipid Parameters in Individuals with Prediabetes: A Systematic Review and Meta-Analysis of Randomized Trials.Probiotics Antimicrob Proteins · PMID 39806201
Systematic review and meta-analysis on probiotics as treatment for food allergies among pediatric patients: A 2024 update.Pediatr Allergy Immunol · PMID 39803979
Efficacy of Oral Probiotic Supplementation in Preventing Vulvovaginal Infections During Pregnancy: A Randomized and Placebo-Controlled Clinical Trial.Nutrients · PMID 39771026
Clinical effects of probiotics on the treatment of gingivitis and periodontitis: a systematic review and meta-analysis.BMC Oral Health · PMID 40186219
Evaluation of the efficacy of probiotics in the chemoradiotherapy of colorectal cancer: a meta-analysis of Randomized Controlled Trials.BMC Gastroenterol · PMID 40301781
Clinical efficacy of probiotic supplementation in the treatment of knee osteoarthritis: a meta-analysis.Front Microbiol · PMID 40276226
The effect of probiotics on select cognitive domains in mild cognitive impairment and Alzheimer's disease: A systematic review and meta-analysis.J Alzheimers Dis Rep · PMID 40034358
Efficacy of probiotic supplementation in influencing cognitive function in Alzheimer's disease: A systematic review and meta-analysis.J Food Sci · PMID 40709497
Effectiveness of probiotic supplements on cognitive function in mild cognitive impairment and Alzheimer's disease: A meta-analysis of randomized controlled trials.Gen Hosp Psychiatry · PMID 41237466
Probiotics are a good choice for the treatment of bacterial vaginosis: a meta-analysis of randomized controlled trialReprod Health · PMID 35698149
Efficacy and safety of Saccharomyces boulardii CNCM I-745 for the treatment of pediatric acute diarrhea in China: a systematic review and meta-analysis.Front Cell Infect Microbiol · PMID 40535538
Efficacy of probiotics in reducing the duration and severity of acute gastroenteritis in children: A meta-analysis of randomized controlled trials.J Pediatr Gastroenterol Nutr · PMID 40739406
Investigating the effects of probiotics during the menopause transition: A systematic review & meta-analysis.Clin Nutr ESPEN · PMID 40639456
Effects of probiotic supplements on bone mineral density and bone turnover markers in postmenopausal women: A systematic review.Clin Nutr ESPEN · PMID 40716641
Impact of probiotic supplementation on serum levels of brain-derived neurotrophic factor: GRADE-based dose-response meta-analysis.BMC Nutr · PMID 40790243
Probiotic Supplementation and Inflammatory Status in Coronary Artery Disease: A Systematic Review and Meta-Analysis.Microorganisms · PMID 41156763

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