Can Probiotics Ease Knee OA Symptoms Through the Gut?

The gut may influence knee osteoarthritis—but it has not solved it

A probiotic will not rebuild worn knee cartilage. But two randomized trials suggest that changing the gut environment may modestly improve knee osteoarthritis symptoms and physical function over 12 weeks. The most unusual result came from a 2025 trial: participants taking a high-dose multistrain probiotic improved on clinical balance tests as plasma zonulin and C-reactive protein (CRP) fell. That finding is intriguing because it connects a gut-barrier marker with something patients feel in daily life: steadier movement.

The evidence is early. The trials were short, small, and measured symptoms, performance, and blood markers—not cartilage loss on MRI or X-ray. Still, the convergence is worth examining. A multibacterial formula and the yeast Saccharomyces boulardii produced symptom-related benefits in separate placebo-controlled trials, despite being very different interventions.

The reasonable conclusion is modest: probiotics may be a low-risk adjunct for some people with knee OA, especially those with obesity or metabolic issues. They are not disease-modifying treatment until trials show that they change the joint itself.

Why the gut could affect a knee

The proposed gut-joint pathway begins with intestinal permeability. When the intestinal barrier is more permeable, bacterial products such as lipopolysaccharide (LPS) may enter circulation more readily. In the joint, LPS can activate innate immune signaling, including TLR4-related pathways, which can promote inflammatory cytokines such as IL-1β and TNF-α. Those signals are relevant to synovial inflammation and cartilage breakdown.

A 2022 systematic review by Guido et al. mapped this hypothesis across 19 studies, including 10 preclinical studies and eight human clinical or ex vivo studies. The biology is plausible, particularly the LPS-to-TLR signaling route. It does not establish that intestinal permeability causes knee OA in people. The review excluded one human study for serious risk of bias, and rated three other human studies at moderate risk of bias.

That distinction matters. A lower zonulin result is a biomarker result. It can support a proposed mechanism, but it cannot prove that repairing the gut barrier caused better balance, less pain, or slower joint damage.

A high-dose multistrain probiotic improved symptoms and balance

In a 2025 double-blind, placebo-controlled trial by Karim et al., 147 adults aged 64 to 75 with knee OA were assigned to a multistrain Vivomix formula or placebo for 12 weeks. The probiotic dose was 112 billion CFU per day. The analysis included 136 participants.

Compared with placebo, the probiotic group had statistically significant improvements in total WOMAC score, visual analog scale pain, handgrip strength, gait speed, and clinical postural-balance tests; all reported P values were below 0.05. Plasma zonulin and CRP also declined significantly. The publication information provided does not report effect sizes or confidence intervals for those outcomes, so the size and clinical importance of the benefit cannot be judged from statistical significance alone.

The balance finding gives the trial its most interesting angle. Participants completed standing, semi-tandem, and tandem stance tests, and balance scores correlated with reductions in zonulin and CRP in the probiotic arm but not the placebo arm. That is an association within one trial, assessed after the fact. It could reflect a gut-barrier pathway, but it could also partly reflect less pain, better confidence while standing, or ordinary measurement variation. Clinical stance tests are useful screening tools, not the same as force-plate measurements that quantify postural control.

The trial also had important null results. Range of motion and resting pain did not improve, and 8-isoprostanes—a marker related to oxidative stress—did not change significantly. The intervention may have helped dynamic function without changing joint mobility, but the pattern does not support a simple claim that probiotics broadly reverse oxidative stress.

A yeast probiotic points in the same direction

A separate 2024 triple-blind, placebo-controlled trial by Dolatkhah et al. studied S. boulardii in overweight and obese people with knee OA. Unlike Vivomix, S. boulardii is a yeast rather than a bacterial mixture. The trial reported improvements in WOMAC pain indices, high-sensitivity CRP, and malondialdehyde (MDA), a lipid-peroxidation marker, versus placebo over the reported 12-week intervention. The available publication summary does not provide the exact analyzed sample size, effect estimates, confidence intervals, or P values for those outcomes.

This study strengthens the case for further research because two structurally distinct probiotics reached similar symptom and inflammation-related endpoints. It does not prove that they worked through the same pathway. The yeast trial found lower MDA, whereas the Vivomix trial found no significant change in 8-isoprostanes. Both markers relate to oxidative stress, but they are not interchangeable. Differences in the interventions, assays, or the exclusively overweight/obese population could explain the disagreement.

Other trials broaden the signal, but independence remains limited

Several newer trials add to the picture. A 2026 randomized trial of a heat-killed Clostridium butyricum postbiotic tested a non-live intervention in adults with mild-to-moderate knee OA and explicitly targeted short-chain-fatty-acid biology. An exploratory 2025 trial of Latilactobacillus sakei LB-P12 adds a defined single-strain test, but its authors describe it as exploratory, so it cannot confirm efficacy on its own.

A related 2025 butyrate intervention reported lower LPS-binding proteins and improved physical function in people with knee OA. That result fits the gut-LPS hypothesis because butyrate is a short-chain fatty acid produced by some gut bacteria. It is supportive, not definitive: multiple trials from this literature share the same lead author, and independent replication remains thin.

Broader reviews also support biological plausibility. A 2025 review of microbiota and OA describes links among dysbiosis, metabolic endotoxemia, and OA severity. Observational links can identify a target for testing; they cannot show that changing the microbiome treats the disease.

What a sensible trial looks like

For someone with knee OA, probiotics belong behind the treatments that already have a clearer place in care: exercise therapy, strength work, weight management when relevant, physical therapy, and medication when appropriate. Do not replace those measures with a capsule.

If you want to try a probiotic as an adjunct, the studies offer a practical but limited template: a 12-week course of either a multistrain formula or S. boulardii, while tracking pain, walking tolerance, and function. The direct evidence for 112 billion CFU per day applies only to the Vivomix trial; it does not show that every product with 10 billion CFU, or any other strain combination, will work. People who are immunocompromised or severely ill should discuss probiotic use with their clinician because even generally low-risk products are not risk-free for every patient.

The missing evidence is as important as the positive signal. No OA probiotic trial cited here used imaging to show cartilage preservation or slower structural progression. None reported what happened after participants stopped treatment. Seven participants withdrew from the Vivomix group and four from placebo, an imbalance that deserves fuller tolerability reporting. Until longer, independently replicated trials include objective function measures and imaging, probiotics remain a plausible symptom-focused experiment—not proof that fixing the gut fixes the knee.