The Gut-Joint Axis: How Your Gut Health Influences Joint Inflammation

When discussing joint pain or arthritis, the gut is unlikely to be most people’s first thought. Yet, emerging research highlights a compelling link between the gut microbiome (the trillions of bacteria residing in your digestive system) and joint inflammation. This connection is known as the gut-joint axis.

Rheumatologist Dr Tan Teck Choon elaborates on the growing evidence linking gut health and joint conditions such as arthritis.

What is the Gut-Joint Axis?

The gut-joint axis refers to the relationship between the gut (especially the microbiome, or the community of bacteria living in your digestive system) and your joints. Scientists have discovered that imbalances in gut bacteria, known as dysbiosis, can trigger inflammation in the body, including in the joints.

A healthy gut microbiome is one where there is a healthy diversity of microorganisms inhabiting the gut, with no single bacteria, virus, or fungus dominating. Although our microbiomes are resilient overall, chronic or heavy exposure to certain factors, such as antibiotics, environmental toxins, physical or psychological stress, or a chronic disease, could affect the microbiome in your gut, leading to dysbiosis.

Studies have found that people with arthritis often have gut dysbiosis, which may weaken the gut lining and increase its intestinal permeability, making it “leakier,” allowing bacteria or toxins to enter the bloodstream or triggering the immune system to attack the joints.

In other words, what happens in your gut may not stay in it—it could contribute to joint inflammation and disease.

Common Joint Conditions Affected by Gut Health

Several types of arthritis have been increasingly linked to our gut health, with gut dysbiosis emerging as a possible contributor to their onset or progression

• Osteoarthritis (OA) is the most common form, often called a “wear-and-tear” condition. It typically develops with age or through repeated use of specific joints, most commonly the knees, hips, and hands. Although OA is largely considered mechanical, emerging evidence suggests that low-grade inflammation is potentially linked to gut health and may play a role in its progression.
• Rheumatoid Arthritis (RA), by contrast, is an autoimmune condition in which the body’s immune system mistakenly attacks the synovium, the lining of the joints, causing chronic inflammation. This can result in severe joint pain, swelling, and eventual joint deformity. Unlike OA, RA can affect the entire body and is often accompanied by fatigue, weight loss, and systemic symptoms. Research has begun to highlight how oral and gut bacteria might influence immune regulation, possibly contributing to the overactive immune responses seen in RA.
• Spondyloarthritis (SpA) refers to a group of inflammatory joint diseases that includes Ankylosing Spondylitis (AS) and Psoriatic Arthritis (PsA). These conditions frequently target the spine and sacroiliac joints, causing pain, stiffness, and, in severe cases, fusion of the spinal vertebrae.
  
  What sets SpA apart is its strong association with genetic factors such as the HLA-B27 gene, a gene that plays a major role in the immune system’s ability to recognise and respond to infections, and gut inflammation. Studies show that even people with risk genes but no symptoms can have changes in their gut bacteria, suggesting these imbalances may come before or worsen joint inflammation.

Collectively, these conditions illustrate a growing sign: our gut health may be far more intertwined with inflammatory joint diseases than we once believed.

Microbial Patterns in Arthritis

Patients with inflammatory arthritis often show significant differences in gut bacteria compared to healthy individuals. Certain strains, such as Prevotella, Bacteroides, and Ruminococcus gnavus, appear more frequently in those with arthritis, potentially driving inflammation. Microbial patterns also vary by geography; for example, dominant bacteria in Chinese AS patients differ from those in Swedish populations.

Gut-Focused Treatments

While there's no definitive cure for arthritis, and current treatments focus on pain and inflammation, new gut-related therapies are being explored. These include Anti-TNF therapies, which may restore microbial balance and increase beneficial gut bacteria, reducing disease flare-ups. In contrast, Anti-IL17 therapies showed a decrease in good gut bacteria and an increase in gut fungi, potentially raising the risk of inflammatory bowel disease.

JAK inhibitors like Fligotinib and Tofacitinib have been observed to boost good gut bacteria production and reduce gut permeability without significantly altering overall microbial composition. Finally, Faecal Microbiota Transplant (FMT) is an experimental therapy that aims to repopulate the gut with healthy microbiomes from a donor's stool.

The Role of Probiotics

Probiotics are live microorganisms administered in adequate amounts to confer health benefits to us, such as by aiding in maintaining a healthy microbiome and assisting in the restoration of gut microbiome balance after dysbiosis.

Although probiotics hold promise as a treatment method, results from studies conducted remain mixed:

• In RA, some studies report reduced inflammation markers, though joint symptoms often remain unchanged.
• In OA, certain trials suggest improved mobility and pain relief by modulating the balance of positive gut microbiome and reducing the effects of low-grade inflammation through various pathways.
• In SpA, more research is needed to determine the efficacy of probiotics.

Probiotics may support treatment but are not yet considered a reliable standalone option.

How Gut Bacteria Interact with Medication

The field of pharmamicrobiomics shows us the ways our gut microbes significantly influence how drugs are processed and their efficacy. These tiny gut bacteria can have a big impact, from activating drugs, such as when they transform sulfasalazine into its anti-inflammatory form, to inactivating medications by converting active metabolites into less bioactive metabolites. They can even create toxic by-products, as seen with harmful forms of diclofenac, an NSAID used to treat pain and swelling.

These interactions may explain why individuals respond differently to the same drug. While the gut-joint connection shows promise, challenges remain. Gut-focused treatments are still largely experimental, with no guaranteed method for prevention or cure. More research is needed to enable truly personalised therapies.

Your gut does more than aid digestion–it may influence your joints, your immune system, and how treatments work. While science continues to evolve, supporting your gut through a healthy lifestyle and diet remains essential.