Kefir
Also called kefir, milk kefir, kefir drink, fermented milk kefir, kefir grains, lactose-free kefir.
Best grade C across 10 graded outcomes Other Last checked
The short answer
From 17 sourcesKefir is a fermented milk drink studied as a food, not a capsule. Small trial pools found lower fasting insulin and insulin resistance, but no change in blood pressure, cholesterol or weight. Kefir also cut breath hydrogen after a lactose load, and in one trial it raised H. pylori clearance when added to antibiotics.
Every graded outcome on this page
10 rows · line = participants- CGrade CFasting blood sugar and insulinBlood sugarn 323
- CGrade CFasting insulin and insulin resistanceInsulin resistancen 314
- CGrade CCholesterol compared with low-fat milkCholesteroln 75
- DGrade DH. pylori clearance with antibiotic triple therapyH. pylorin 82
- DGrade DLiver enzymes and metabolic markers in fatty liver diseaseFatty livern 72
- DGrade DGut symptoms, sleep and mood in healthy young adultsGut symptomsn 65
- DGrade DADHD symptoms and sleep in childrenADHDn 53
- DGrade DLactose digestion and gas after a lactose loadLactose tolerancen 15
- DGrade D5 km running time trial after exhausting exerciseExercise performancen 11
- ∅No effectBlood pressure and C-reactive proteinBlood pressuren 385
- 7 more graded outcomes, in the evidence chapter
Key facts
- What it is
- Milk fermented by the bacteria and yeasts in kefir grains; studied as a drink2
- Insulin (6 trials, 314 people)
- Fasting insulin -3.69 µIU/mL and HOMA-IR -2.56; no change in glucose, HbA1c, lipids or weight2
- Glucose (24 studies, 2026)
- A 2026 meta-analysis found fasting glucose -8.46 mg/dL and HOMA-IR -1.71, with no change in weight, lipids or inflammation markers10
- Blood pressure (7 trials, 385 people)
- No significant change in systolic or diastolic pressure or CRP4
- Lactose (15 adults)
- Plain kefir cut breath hydrogen to 87 vs 224 ppm·h after milk5
- Safety in intensive care
- No kefir-related bloodstream infections in 54 critically ill adults given up to 240 mL a day14
What it is
Kefir is a fermented milk drink made with kefir grains, a mix of bacteria and yeasts; trials dosed it in millilitres, not capsules.
Forms, side by side
2 forms named in our sources. The rest show what our data holds, and say plainly where it holds nothing yet.
Kefir forms compared
2 forms| 2 forms | Milk kefir drink | Lactose-free kefir |
|---|---|---|
| Absorption in people | Not measured as a nutrient; trials tracked insulin, lipids, gut symptoms and breath hydrogen.25 | Not measured; the trial tracked gut symptoms, blood markers, sleep and mood.7 |
| GI tolerance | Plain kefir lowered breath hydrogen and flatulence vs milk in adults with lactose maldigestion; abdominal pain and diarrhoea were negligible.5 | 250 mL a day for 6 weeks was used in healthy young adults; the abstract reports no safety problems.7 |
| Studied for | Insulin and blood sugar, cholesterol, blood pressure, lactose digestion, H. pylori clearance | Gut symptoms, sleep and mood in healthy adults |
- Milk kefir drink
- Absorption in people
- Not measured as a nutrient; trials tracked insulin, lipids, gut symptoms and breath hydrogen.25
- GI tolerance
- Plain kefir lowered breath hydrogen and flatulence vs milk in adults with lactose maldigestion; abdominal pain and diarrhoea were negligible.5
- Studied for
- Insulin and blood sugar, cholesterol, blood pressure, lactose digestion, H. pylori clearance
- Lactose-free kefir
What the human research says
Human trials only, one row per outcome. The form line shows what each trial actually tested. Grades follow our evidence-grading policy.
Trial map
10 graded outcomes, largest study first10 graded outcomes: 4 improved, 2 mixed, 4 no effect. The largest, a 2025 meta-analysis of 385 people on blood pressure and C-reactive protein, found no effect.
1Blood pressure and C-reactive protein
No effect · No-effect grade · Meta-analysis, 385 people, 2025
Adults in 7 RCTs, kefir for at least 2 weeks
Dose, result and source| Outcome | Found | People | Study | Who was studied |
|---|---|---|---|---|
| Blood pressure and C-reactive protein | No effect | 385 | No-effect grade · Meta-analysis, 2025 | Adults in 7 RCTs, kefir for at least 2 weeks |
| Fasting blood sugar and insulin | Improved | 323 | Grade C · Meta-analysis, 2021 | Adults in 6 RCTs |
| Fasting insulin and insulin resistance | Improved | 314 | Grade C · Meta-analysis, 2023 | Adults in 6 RCTs |
| H. pylori clearance with antibiotic triple therapy | Improved | 82 | Grade D · RCT, 2011 | Adults with dyspepsia and confirmed H. pylori on 14-day lansoprazole, amoxicillin and clarithromycin |
| Cholesterol compared with low-fat milk | No effect | 75 | Grade C · RCT, 2017 | Overweight or obese premenopausal women aged 25 to 45 on a dairy-rich diet |
| Liver enzymes and metabolic markers in fatty liver disease | No effect | 72 | Grade D · RCT, 2025 | Adults with non-alcoholic fatty liver disease on a diet plan (Iran); 72 of 80 completed |
| Gut symptoms, sleep and mood in healthy young adults | Mixed | 65 | Grade D · RCT, 2026 | Healthy young adult volunteers |
| ADHD symptoms and sleep in children | Mixed | 53 | Grade D · RCT, 2025 | Children aged 8-13 with ADHD (UK); 53 completed |
| Lactose digestion and gas after a lactose load | Improved | 15 | Grade D · Crossover RCT, 2003 | Healthy adults with lactose maldigestion |
| 5 km running time trial after exhausting exercise | No effect | 11 | Grade D · Crossover RCT, 2024 | Endurance master athletes, men and women |
Every graded row
10 rowsShowing 10 of 10 outcomes. Human trials only.
CGrade CFasting blood sugar and insulinBlood sugarLower fasting glucoseMeta-analysis · 6 studies
n 323 · 2021
Improved Fasting blood sugar fell 10.28 mg/dL and insulin 2.87 µIU/mL; the HbA1c drop of 0.64 points was not significant (p = 0.08).
- Design
- Meta-analysis, 6 studies, n = 323, 2021
- Population
- Adults in 6 RCTs
- Form
- Kefir drink
- Dose
- Varied by trial
- Duration
- Varied by trial
- Source
- Reference 3 · PubMed 34280689 (opens PubMed)
CGrade CFasting insulin and insulin resistanceInsulin resistanceLower insulin, HOMA-IRMeta-analysis · 6 studies
n 314 · 2023
Improved Fasting insulin fell 3.69 µIU/mL (p = 0.006) and HOMA-IR 2.56 (p < 0.001); fasting glucose, HbA1c, total, LDL and HDL cholesterol, triglycerides and body weight did not change.
- Design
- Meta-analysis, 6 studies, n = 314, 2023
- Population
- Adults in 6 RCTs
- Form
- Kefir drink
- Dose
- Varied by trial
- Duration
- Varied by trial
- Source
- Reference 2 · PubMed 37102491 (opens PubMed)
CGrade CCholesterol compared with low-fat milkCholesterolSame as milkRCT
n 75 · 2017
No effect Kefir lowered LDL by 9.7 mg/dL and total cholesterol by 10.4 mg/dL vs the control diet, but milk did the same, and kefir and milk did not differ.
- Design
- RCT, n = 75, 2017
- Population
- Overweight or obese premenopausal women aged 25 to 45 on a dairy-rich diet
- Form
- Kefir drink vs low-fat milk vs control diet
- Dose
- 2 extra dairy servings a day as kefir or milk
- Duration
- 8 weeks
- Source
- Reference 6 · PubMed 28391880 (opens PubMed)
DGrade DH. pylori clearance with antibiotic triple therapyH. pyloriHigher clearanceRCT
n 82 · 2011
Improved Clearance was 78.2% (36 of 46) with kefir vs 50.0% (18 of 36) with placebo milk (p = 0.026), and side effects were less frequent and less severe.
- Design
- RCT, n = 82, 2011
- Population
- Adults with dyspepsia and confirmed H. pylori on 14-day lansoprazole, amoxicillin and clarithromycin
- Form
- Kefir vs milk with placebo, alongside antibiotics
- Dose
- 250 mL twice a day
- Duration
- 14 days
- Source
- Reference 8 · PubMed 21186984 (opens PubMed)
DGrade DLiver enzymes and metabolic markers in fatty liver diseaseFatty liverNo change in liver enzymesRCT
n 72 · 2025
No effect No significant difference from diet alone in liver enzymes, blood pressure, body measurements or other lab markers, except HDL cholesterol (p = 0.02) and fat-free mass (p < 0.001).
- Design
- RCT, n = 72, 2025
- Population
- Adults with non-alcoholic fatty liver disease on a diet plan (Iran); 72 of 80 completed
- Form
- Kefir drink plus diet vs diet alone
- Dose
- 500 mL/day (a cup twice daily)
- Duration
- 8 weeks
- Source
- Reference 12 · PubMed 39773657 (opens PubMed)
DGrade DGut symptoms, sleep and mood in healthy young adultsGut symptomsFewer gut symptomsRCT
n 65 · 2026
Mixed Gastrointestinal symptoms and serum cholesterol, creatinine and uric acid fell; changes in glucose, CRP, sleep quality and mental-health scores were not significant, and immunity and inflammation markers did not improve. Some body measurements rose.
- Design
- RCT, n = 65, 2026
- Population
- Healthy young adult volunteers
- Form
- Lactose-free kefir
- Dose
- 250 mL a day
- Duration
- 6 weeks
- Source
- Reference 7 · PubMed 41314291 (opens PubMed)
DGrade DADHD symptoms and sleep in childrenADHDNo change in ADHD symptomsRCT
n 53 · 2025
Mixed No significant effect on parent- or teacher-rated ADHD symptoms (SWAN). On actigraphy, children on kefir spent less time awake in bed at week 6 (about 70 vs 90 minutes, p = 0.04), but self-reported sleep problems were slightly higher (p = 0.02). Several Bifidobacterium species increased.
- Design
- RCT, n = 53, 2025
- Population
- Children aged 8-13 with ADHD (UK); 53 completed
- Form
- Cow's milk kefir vs placebo drink
- Dose
- 125 mL/day
- Duration
- 6 weeks
- Source
- Reference 11 · PubMed 41286799 (opens PubMed)
DGrade DLactose digestion and gas after a lactose loadLactose toleranceLess breath hydrogenCrossover RCT
n 15 · 2003
Improved Breath hydrogen was 87 ppm·h with plain kefir vs 224 with milk (p < 0.001); flavoured kefir was intermediate (156). Kefirs and yogurts cut flatulence severity by 54 to 71% vs milk.
- Design
- Crossover RCT, n = 15, 2003
- Population
- Healthy adults with lactose maldigestion
- Form
- Plain and raspberry kefir vs 2% milk and yogurts
- Dose
- Test meals with 20 g lactose
- Duration
- Single test meals, 8 hours each
- Source
- Reference 5 · PubMed 12728216 (opens PubMed)
DGrade D5 km running time trial after exhausting exerciseExercise performanceNo faster timesCrossover RCT
n 11 · 2024
No effect 5 km times did not differ (water 33:39, kefir 33:41, milk 33:36 min:s; p = 0.99); gut-symptom scores after the exhausting exercise were lower with kefir than with water (p = 0.005).
- Design
- Crossover RCT, n = 11, 2024
- Population
- Endurance master athletes, men and women
- Form
- Flavoured kefir vs flavoured milk vs water
- Dose
- Amount not given in the abstract
- Duration
- 14 days of kefir before the test day
- Source
- Reference 13 · PubMed 38474845 (opens PubMed)
∅No effectBlood pressure and C-reactive proteinBlood pressureNo changeMeta-analysis · 7 studies
n 385 · 2025
No effect No significant change in systolic (-1.76 mmHg, p = 0.317) or diastolic pressure (-1.19 mmHg) or CRP (-0.17 mg/L); in a subgroup, CRP fell with 8 weeks or more.
- Design
- Meta-analysis, 7 studies, n = 385, 2025
- Population
- Adults in 7 RCTs, kefir for at least 2 weeks
- Form
- Kefir drink
- Dose
- Varied by trial
- Duration
- 2 weeks or longer
- Source
- Reference 4 · PubMed 41139305 (opens PubMed)
What the numbers add up to
Each point is worked out from the data and the sources numbered on this page, with the arithmetic shown under it. It adds no new data and is not medical advice.
No better than milk for cholesterol
In 75 women on a dairy-rich diet, kefir lowered LDL by about as much as low-fat milk, so the effect came from the extra dairy.6
Insulin moved, blood pressure did not
Studied doses
Doses used in research, shown against the official limits. They describe the studies, not a recommendation for you.
Studied doses in research, not advice. These are amounts used in research, not personal advice. Your clinician or pharmacist can say what fits you.
Doses studied in human trials
When trials measured an effect
3 outcomes| Outcome | Measured at | Basis |
|---|---|---|
| Breath hydrogen after a lactose load | Same meal (measured over 8 hours) | Single test meals with 20 g of lactose in 15 adults5 |
| H. pylori clearance with triple therapy | Breath test 45 days after starting the 14-day course | 250 mL kefir twice daily alongside antibiotics in 82 adults8 |
| Time awake in bed in children with ADHD (actigraphy) | Week 6 (end of trial) | 125 mL/day kefir vs placebo drink11 |
Interactions and safety
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
What Kefir meets
1 cited rowMedicines 1
Supplements and foods 0
No supplement rows in our sources.
- Reference summary
Choose a medicine or supplement above to read its cited rows here.
Interactions
1 agentCheck with what you take
Kept on this device onlyAdd what you take. We list every interaction our evidence profiles cite between Kefir and your picks, and between your picks.
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Add a supplement or medicine you take to check it against Kefir.
Starting from one medicine? The interaction checker rates how serious each pair is, on a curated list of 19 entries for 11 medicines. This cabinet has no severity rating: it lists every interaction row our supplement pages cite.
Who should be careful
5 groups- Weakened immune system or serious illness
- NCCIH says the risk of harmful effects from probiotics is greater in people with severe illnesses or compromised immune systems. In a 54-patient intensive-care safety study, kefir caused no bloodstream infections; two patients also on laxatives had diarrhea.114
- Premature infants
- NCCIH notes severe or fatal infections in premature infants given probiotics, and an FDA warning to health care providers.1
- Pregnancy and breastfeeding
- No kefir trial has studied pregnancy or breastfeeding. A 2009 meta-analysis of Lactobacillus and Bifidobacterium trials in 1,505 pregnant women found no effect on caesarean rates, birth weight or gestational age and no malformations, but trials of yeasts were lacking, and kefir also contains yeasts. FDA advises pregnant women and others at higher risk of foodborne illness to avoid foods made with unpasteurized milk, which includes raw-milk kefir.15216
- Lactose maldigestion
- Regular kefir is a milk drink: the lactose test fed kefir portions with 20 g of lactose. Plain kefir cut breath hydrogen but did not remove it; lactose-free kefir exists.57
- Medicines and surgery
- NCCIH advises telling your health care providers about every supplement you use, since some interact with medicines or pose risks before surgery.9
How to read the label
What to check on the Supplement Facts panel.
Frequently asked questions
Short answers to common questions; the numbers link to the sources below.
Common questions
8 answersDoes kefir lower blood sugar?
Does kefir lower blood pressure or cholesterol?
Can people with lactose intolerance drink kefir?
Does kefir help with H. pylori?
In 82 adults on 14-day triple therapy, adding 250 mL of kefir twice a day raised clearance to 78% vs 50% with placebo milk. Kefir was an add-on to antibiotics, not a replacement.8
Is kefir safe for everyone?
NCCIH says probiotic risks are greater for people with serious illness or weakened immunity, and severe infections have occurred in premature infants given probiotics.1
Is it safe to drink kefir every day?
Can kefir be taken with antibiotics?
Is kefir better than yogurt or probiotic capsules?
No trial has compared kefir with probiotic capsules. In a lactose test, plain kefir and plain yogurt cut breath hydrogen about equally; flavoured kefir cut it less than plain kefir.5
Sources
17 sources: trial abstracts, NIH fact sheets and reference databases. Numbers in the text link here.
Sources cited on this page
17 sources- 1Probiotics: Usefulness and Safety (last updated August 2019)Fact sheet National Center for Complementary and Integrative Health (NCCIH), 2019 · nccih.nih.gov
- 2Effects of Kefir Consumption on Cardiometabolic Risk Factors: A Systematic Review and Meta-analysis of Randomized Controlled Trials.Meta-analysis Curr Drug Targets, 2023 · PMID 37102491
- 3Effect of kefir beverage consumption on glycemic control: A systematic review and meta-analysis of randomized controlled clinical trials.Meta-analysis Complement Ther Clin Pract, 2021 · PMID 34280689
- 4The Effect of Kefir Consumption on Blood Pressure and C-Reactive Protein: A Systematic Review and Meta-Analysis of Randomised Controlled Trials.Meta-analysis Endocrinol Diabetes Metab, 2025 · PMID 41139305
- 5Kefir improves lactose digestion and tolerance in adults with lactose maldigestion.Crossover RCT J Am Diet Assoc, 2003 · PMID 12728216
- 6Kefir drink causes a significant yet similar improvement in serum lipid profile, compared with low-fat milk, in a dairy-rich diet in overweight or obese premenopausal women: A randomized controlled trial.RCT J Clin Lipidol, 2017 · PMID 28391880
- 7Effects of Kefir Consumption on Gastrointestinal Health, Biochemical Parameters, Sleep, and Mental Well-Being in Healthy Young Adults: a Randomized Controlled Trial.RCT J Nutr, 2026 · PMID 41314291
- 8Kefir improves the efficacy and tolerability of triple therapy in eradicating Helicobacter pylori.RCT J Med Food, 2011 · PMID 21186984
- 9Using Dietary Supplements WiselyFact sheet National Center for Complementary and Integrative Health (NCCIH), 2019 · nccih.nih.gov
- 10Effect of different kefir dosages on inflammation status, metabolic profile, and anthropometric measurements in adults: A systematic review and meta-analysis.Meta-analysis Nutr Metab Cardiovasc Dis, 2026 · PMID 41076330
- 11Effects of kefir on symptoms, sleep, and gut microbiota in children with ADHD: a randomised controlled trial.RCT BMC Psychiatry, 2025 · PMID 41286799
- 12The effects of kefir drink on liver aminotransferases and metabolic indicators in patients with nonalcoholic fatty liver disease: a randomized controlled trial.RCT BMC Nutr, 2025 · PMID 39773657
- 13Milk or Kefir, in Comparison to Water, Do Not Enhance Running Time-Trial Performance in Endurance Master Athletes.Crossover RCT Nutrients, 2024 · PMID 38474845
- 14Safety, feasibility, and impact on the gut microbiome of kefir administration in critically ill adults.Open-label trial BMC Med, 2024 · PMID 38378568
- 15Probiotic safety in pregnancy: a systematic review and meta-analysis of randomized controlled trials of Lactobacillus, Bifidobacterium, and Saccharomyces spp.Meta-analysis J Obstet Gynaecol Can, 2009 · PMID 19646321
- 16People at Risk of Foodborne IllnessFact sheet U.S. Food and Drug Administration, 2025 · fda.gov
- 17Ciprofloxacin: MedlinePlus Drug InformationFact sheet MedlinePlus, 2026 · medlineplus.gov
What changed
Every dated change to this page: what changed, who made it and why.
Change log
2 entries| Date | Change | Who and why |
|---|---|---|
| key facts, evidence, studied doses, interactions, who should avoid, FAQ, questions, time to effect, related | Added a pregnancy and breastfeeding note (no kefir data; a 2009 meta-analysis of probiotic bacteria in 1,505 pregnant women found no harm signal but no yeast trials; FDA advice to avoid foods made with unpasteurized milk); LactMed and LiverTox have no kefir or probiotic entry. Added three trials: ADHD in children (2025, 53 children, 125 mL/day for 6 weeks: no change in ADHD symptoms, mixed sleep results; grade D), fatty liver disease (2025, 72 adults, 500 mL/day for 8 weeks: no change in liver enzymes; grade D) and a 5 km running test (2024, 11 athletes: no faster times; grade D). Added a 2026 meta-analysis of 24 studies as a key fact only (fasting glucose -8.46 mg/dL, HOMA-IR -1.71; its abstract gives no participant total) and an intensive-care safety study (54 patients, no kefir-related bloodstream infections). Interaction: MedlinePlus advice not to take ciprofloxacin with dairy products alone. Updated studied doses to 125-500 mL/day; added FAQ items on antibiotics, kefir versus yogurt or capsules and daily use, time-to-effect rows, page questions and goal-hub links. Not added: a 2026 post-exercise recovery crossover and a 2025 soccer study without a between-group performance result. | Writer: Kymata Health EditorialTrigger: A–Z audit against docs/supplements/AUDIT-STANDARD.md |
| all | Initial editorial evidence review. Every PMID checked against NCBI E-utilities esummary (title, year, journal) and each cited abstract read; numbers taken from the abstracts. Kefir graded as a food dosed by volume; the cholesterol trial is shown as no better than milk, the blood-pressure pool as no effect, and H. pylori as an add-on to antibiotics only. Safety from the NCCIH probiotics fact sheet. Where to buy: we didn’t list a product; none of the stores we checked sells kefir. | Writer: Kymata Health EditorialTrigger: new page |
Supplement & Nutrient Encyclopedia. Educational information only; it is not medical advice and does not replace a clinician. Dietary supplements are not intended to diagnose, treat, cure or prevent any disease. Statements about supplements have not been evaluated by the FDA.