Your Shoulder Pain Might Start in Your Gut, New Study Suggests

If your shoulder has been aching for months and physical therapy or injections have not fully fixed it, you have probably already researched every mechanical explanation: overuse, poor posture, a partial tear that will not quite heal. A new study asks a different question entirely: does the health of your gut have anything to do with it. Researchers in China compared the gut bacteria and blood chemistry of people with worn, degenerating rotator cuff tendons to healthy people the same age, and found a distinct pattern separating the two groups.

Key takeaways:

• In a 121 person case control study, people with symptomatic degenerative rotator cuff tendinopathy (dRCT) had a measurably different gut bacterial community and blood metabolite profile than matched healthy controls.
• The dRCT group was enriched in bacteria linked to inflammation and endotoxin production, while controls retained more of the short chain fatty acid producing bacteria that support gut barrier health and tissue repair.
• Blood levels of several tryptophan derived indole compounds, byproducts your gut bacteria make that help calm inflammation, were consistently lower in the tendon disease group.
• This is a single, cross sectional study. It shows an association, not proof that gut bacteria cause tendon damage, and nothing here supports taking a specific probiotic or supplement yet.

Gut Bacteria Composition Differs in Rotator Cuff Tendon Disease

Researchers found that people with symptomatic degenerative rotator cuff tendinopathy (dRCT, chronic wear related damage to the tendons that stabilize the shoulder joint, distinct from an acute traumatic tear) carry a different mix of gut bacteria than matched healthy people, according to a study published in Frontiers in Microbiology. The team, led by Yanzi Liu and Wendan Cheng at the Second Affiliated Hospital of Anhui Medical University, ran stool DNA sequencing (16S rRNA sequencing, a method that identifies which bacterial species are present by reading a shared bacterial gene) and blood chemistry testing on 121 total participants. Overall bacterial diversity, meaning how many different species were present, was not different between groups. But the overall composition, which specific species dominated, separated the two groups with statistical significance (P = 0.014 by one test, P = 0.007 by another), even though the researchers describe the size of that separation as modest. The dRCT group was enriched in the phyla Bacteroidota and Pseudomonadota, and in genera including Segatella, Megamonas, Klebsiella, Desulfovibrio, Agathobacter and Alistipes. The healthy control group retained more Bacillota, and more of two specific short chain fatty acid (SCFA, a beneficial byproduct bacteria make by fermenting fiber) producing genera called Gemmiger and Eubacterium_ruminantium.

Rotator Cuff Disease Already Affects Millions of Older Adults

Degenerative rotator cuff tendinopathy is not a rare condition. It affects more than 15% of adults over age 60, and becomes more common with age, according to prior epidemiological work the authors cite. It is a leading cause of chronic shoulder pain, weakness and lost range of motion, and even after surgical repair, tendons re-tear at a rate of 20% to 60%. That high failure rate is exactly why researchers are looking beyond the shoulder joint itself: if the systemic, whole body inflammation reflected in gut bacteria composition is part of what breaks tendons down in the first place, mechanical repair alone would not be expected to fully solve the problem, which is broadly consistent with patterns seen in other joint conditions like osteoarthritis, where dysbiosis has been proposed as a modifiable risk factor.

How Researchers Compared 121 Patients and Matched Controls

This was a case control study, meaning the researchers compared an already affected group to a similar but unaffected group, rather than following people over time. The dRCT group, confirmed by clinical exam and MRI imaging showing tendon degeneration, started at 61 patients and finished at 60 after one participant was excluded for an insufficient stool sample; the control group had 61 healthy volunteers matched for age, sex and body mass index (BMI), so the two groups looked alike on paper going in. Everyone gave a stool sample for 16S rRNA sequencing and a fasting blood sample for untargeted metabolomics (a technique that measures hundreds to thousands of small molecules in blood at once, rather than testing for one substance at a time). The metabolomics scan flagged 309 differentially abundant molecules in one detection mode and 226 in another, and the majority of those held up after a statistical correction for testing so many molecules at once. The team also used a computational tool called PICRUSt2 to predict, from the bacterial DNA data alone, which metabolic functions those bacterial communities were likely capable of; this is a prediction based on known bacterial genomes, not a direct measurement of active enzymes.

What the Findings Mean for Gut Health and Inflammation

The practical thread connecting the bacterial and blood chemistry findings is inflammation and gut barrier integrity. PICRUSt2 predicted that the dRCT-associated bacteria were more capable of producing lipopolysaccharide (LPS, a component of certain bacterial cell walls that acts as a potent inflammatory trigger once it crosses into the bloodstream), while the control associated bacteria were predicted to favor pathways tied to amino acid production and tissue repair. In the blood itself, several indole compounds (byproducts your gut bacteria make when they break down the amino acid tryptophan from your diet, which normally help reinforce the gut lining and dial down inflammation) were consistently lower in the tendon disease group, including indole-3-acetaldehyde and indoleacetic acid. Vitamin E, an antioxidant that protects tissue from oxidative damage, was also lower in the dRCT group. None of this means a specific probiotic, prebiotic or supplement is proven to prevent or treat tendon degeneration. The authors describe SCFA and probiotic based interventions as strategies worth testing in future clinical trials, explicitly not as something already validated. If you have chronic shoulder pain, this is a reason to keep an eye on emerging research and to mention persistent gut symptoms to your doctor alongside your orthopedic workup, not a reason to self treat with an untested regimen.

Limitations: Why This Study Cannot Prove Causation

The authors are direct about what this study does and does not show. Because it is cross sectional, comparing two groups at a single point in time, it cannot establish that the microbiome changes caused the tendon damage, or the reverse, that having degenerative tendon disease somehow reshaped the gut community. The sample also came from a single research center, which limits how confidently the pattern can be generalized to other populations, and the PICRUSt2 functional predictions are inferential, based on which genes related bacterial species are known to carry, not measurements of what those bacteria were actually doing in each participant's gut at the time. The authors also note they did not implement a standardized washout period for anti-inflammatory painkillers before sample collection, medications known to affect gut permeability and could plausibly be part of what is driving the difference rather than the disease itself. This is also, by the authors' own account, the first study of its kind, so there is no independent replication yet.

What Comes Next for Gut-Tendon Axis Research

The authors call this a first step toward what they term a "gut-tendon axis," and are careful to frame it as hypothesis generating rather than definitive. They point to a separate animal study, in which exercise after rotator cuff surgery altered gut bacteria and predicted healing outcomes in mice, as complementary evidence that the gut and tendon biology are connected through more than one route, alongside supporting mechanistic work on how tryptophan derived indole metabolites support gut barrier integrity more broadly. The next steps the field needs are prospective studies that track people over time to see whether gut changes precede tendon damage, larger multi center samples, and direct metagenomic sequencing to confirm what the bacteria are actually doing rather than what they are predicted to be capable of. No timeline for a follow up trial has been announced.

Common Questions

Does this mean probiotics can fix rotator cuff pain? No. The study found an association between gut bacteria and tendon disease, not proof that changing your gut bacteria would prevent or treat it; the authors describe probiotic and SCFA based approaches as unproven strategies that need dedicated clinical trials.

Is this the same as gut bacteria causing joint pain in general? Similar patterns, bacteria linked to inflammation rising while short chain fatty acid producing bacteria fall, have been reported in osteoarthritis and other musculoskeletal conditions, which is part of why researchers think a broader "gut-joint" pattern may exist, but each condition needs its own evidence.

Should I ask my doctor about my gut health if I have shoulder pain? It is reasonable to mention persistent digestive symptoms alongside a shoulder pain workup, since the research is pointing toward whole body inflammation as a contributor, but there is no established gut test or treatment yet specifically indicated for tendon disease.

Was this study done in animals or humans? Humans. The 121 participants were real patients and matched healthy volunteers; a separate animal study on post-surgical recovery is mentioned only as supporting context.

References

1. Yanzi Liu, Zheng Liu, Bin Zhang, Weijun Wang, Xuedong Tian, Wendan Cheng (2026). Changes in gut microbiota and plasma metabolites in patients with symptomatic degenerative rotator cuff tendinopathy. Frontiers in Microbiology. https://doi.org/10.3389/fmicb.2026.1927912
2. Xiaoxia Hao, Xingru Shang, Jiawei Liu, Ruimin Chi, Jiaming Zhang, Tao Xu (2021). The gut microbiota in osteoarthritis: where do we stand and what can we do?. Arthritis Research & Therapy. https://doi.org/10.1186/s13075-021-02427-9
3. Samantha A. Scott, Jingjing Fu, Pamela V. Chang (2020). Microbial tryptophan metabolites regulate gut barrier function via the aryl hydrocarbon receptor. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.2000047117