Gut health and arthritis

The gut and the joints influence one another more than you might expect. In some people, inflammation in the bowel and inflammation in the joints are part of the same underlying process. In others, an infection passing through the gut sets off a reaction in the joints. And across inflammatory arthritis as a whole, researchers are increasingly interested in the part played by the gut microbiome, the vast community of bacteria that live in the digestive tract. This guide takes each connection in turn, keeps to what the evidence actually shows, and explains when gut symptoms alongside joint pain are worth raising with a specialist.

Crohn's disease and ulcerative colitis, together known as inflammatory bowel disease, are driven by inflammation in the lining of the gut. In some people that same inflammatory process affects the joints and spine, a linked condition called enteropathic arthritis. It sits within the spondyloarthritis family, alongside axial spondyloarthritis.

The joint involvement tends to follow one of two patterns, and a person can have both. Inflammation in the limb joints, such as the knees or ankles, often flares in step with the bowel, so calming the gut inflammation can ease the joints as well. Inflammation in the spine and the joints at the base of the spine tends to run its own course, largely independent of how the bowel is behaving, and needs treating in its own right.

The order of events varies. The bowel disease is usually recognised first, but the joints occasionally become inflamed before the gut condition is diagnosed, which is one reason a rheumatologist will always ask about bowel symptoms. Because the two organs share one underlying disease, treatment is chosen with both in mind, and care tends to work best when the rheumatology and gastroenterology sides are coordinated.

Some bouts of arthritis begin not with a bowel disease but with a bowel infection. Reactive arthritis is joint inflammation that develops as a reaction to an infection elsewhere in the body, and the gut is one of the commonest starting points. Food-poisoning organisms such as salmonella and campylobacter are typical triggers, and the joints usually become inflamed a week or two later, by which time the original gut upset may have settled.

The joints themselves are not infected. Instead the immune system, primed by the infection, mistakenly inflames them, and sometimes the tendons and eyes as well. In most people the arthritis improves over time, though in a minority it persists or comes back. Because a hot, swollen joint can have several causes, it is worth having assessed rather than assumed to be a passing reaction.

The gut is home to trillions of bacteria, collectively called the microbiome, which help to regulate digestion and the immune system. Because so much immune activity happens in and around the gut, there is real scientific interest in whether the make-up of these bacteria influences inflammatory arthritis such as rheumatoid and psoriatic arthritis.

This is an evolving area of research rather than settled fact. Studies have found differences in the gut bacteria of people with inflammatory arthritis compared with others, and work is under way to understand whether those differences are a cause, a consequence, or simply an association. It is a promising field, but it has not yet produced a proven treatment.

For now, that means being honest about what is not known. No probiotic, supplement or special diet has been shown to reliably treat or cure inflammatory arthritis, and claims to the contrary should be treated with caution. A balanced diet is worth pursuing for your general health, and is covered in our guide to diet and arthritis, but it supports your prescribed treatment rather than replacing it.

Coeliac disease is a reaction to gluten that inflames and damages the lining of the small bowel. It is not a form of arthritis, but it connects to the musculoskeletal system in a couple of ways worth knowing about. Some people with undiagnosed coeliac disease report joint or muscle aches alongside their gut symptoms, and these can ease once a gluten-free diet is started.

More firmly established is the effect on the bones. When the damaged bowel cannot absorb nutrients properly, including the calcium needed for strong bones, bone density can fall, which raises the risk of osteoporosis. Bone density usually improves on a gluten-free diet, and where there is concern a bone density scan can assess it.

The practical point is not to go gluten-free on your own in the hope of easing joint pain. Doing so before testing can make coeliac disease harder to diagnose, because the tests rely on gluten being in the diet. If you have unexplained gut symptoms together with joint or bone pain, it is reasonable to ask your GP whether coeliac disease should be tested for, which starts with a simple blood test.

The gut-arthritis relationship runs the other way too, through treatment. Anti-inflammatory tablets (NSAIDs), such as ibuprofen and naproxen, are widely used to ease joint pain and stiffness, but they can irritate the stomach and, with regular or long-term use, increase the risk of ulcers and bleeding in the gut.

This does not mean NSAIDs cannot be used, only that they are used thoughtfully. Taking them with food, using the lowest helpful dose for the shortest sensible time, and being alert to indigestion all help. For people who need them longer term, or who are at higher risk of stomach problems, a doctor will often prescribe a stomach-protecting medicine such as a proton pump inhibitor, for example omeprazole, to take alongside. If you already have inflammatory bowel disease, NSAIDs are used with particular caution, as they can sometimes unsettle the bowel. Anyone who develops black or tarry stools, vomits blood, or has persistent stomach pain while taking them should seek medical advice promptly.

Gut symptoms and joint symptoms are both common, and much of the time they are unrelated. But certain gut symptoms deserve attention in their own right, and mentioning them helps your rheumatologist see the whole picture, particularly if you have, or may have, a spondyloarthritis-type condition.

Tell your rheumatologist or GP if you notice:

• Blood in your stool, or black, tarry stools
• Persistent diarrhoea, especially if it lasts more than a couple of weeks or wakes you at night
• Ongoing stomach pain or cramping
• Unintended weight loss
• Mouth ulcers that keep returning, or new bowel symptoms alongside a joint flare

These symptoms are not something to diagnose yourself. Each needs medical assessment on its own merits, both to check whether the gut and the joints are connected and to make sure nothing else is missed. New or worsening bowel bleeding, severe abdominal pain, or feeling very unwell should be assessed without delay.

The connection between the gut and the joints is real and well recognised in some conditions, such as inflammatory bowel disease and reactive arthritis, and an area of active study in others, such as the microbiome. What holds across all of them is that gut symptoms and joint symptoms each deserve proper assessment rather than assumptions. If you have both, a specialist can work out whether they are linked, check the joints for inflammation, and coordinate care with your gut team where that is needed, so the two are managed together rather than in isolation.

Can problems in my gut cause arthritis?

Sometimes, yes. Inflammation in the bowel, as in Crohn's disease or ulcerative colitis, can come with a linked form of joint inflammation called enteropathic arthritis. A gut infection can also trigger reactive arthritis a week or two later. In both, the joint problem is driven by the immune system rather than by the gut directly, and it is worth assessing in its own right.

Which comes first, the gut symptoms or the joint symptoms?

Either can. In inflammatory bowel disease the bowel problem is usually known first, but the joints sometimes flare before the diagnosis is made. With reactive arthritis the gut infection normally comes first and may have settled by the time the joints react. Telling your rheumatologist about any gut symptoms, past or present, helps join up the picture.

Will a special diet or probiotics fix my inflammatory arthritis?

There is no good evidence that any particular diet or probiotic reliably treats inflammatory arthritis. Research into the gut microbiome and arthritis is genuinely interesting but still at an early stage, and it has not produced a proven treatment. A balanced diet is worth it for your general health, but it supports rather than replaces your prescribed treatment. Our guide to diet and arthritis sets out what the evidence shows.

Can coeliac disease cause joint pain?

Coeliac disease is not a form of arthritis, but some people with it report joint or muscle aches, and left untreated it can weaken the bones through poor absorption of calcium. If you have unexplained gut symptoms alongside joint or bone pain, it is reasonable to ask whether coeliac disease should be tested for. It is best not to go gluten-free before testing, as the tests rely on gluten being in your diet.

I take anti-inflammatory tablets for my joints. Are they bad for my gut?

Anti-inflammatory painkillers (NSAIDs) can irritate the stomach and, with regular use, raise the risk of ulcers or bleeding. This does not mean you cannot use them, but if you take them long term your doctor may prescribe a stomach-protecting medicine such as a proton pump inhibitor, and use the lowest helpful dose. Always mention any indigestion, black stools or persistent stomach pain.