Gut health and arthritis

Most people think of the gut and the joints as separate, but they influence each other in at least four ways. A single inflammatory disease can affect both the bowel and the joints. A bout of food poisoning can provoke joint swelling weeks afterwards. The bacteria that live in the digestive tract, the gut microbiome, are being studied for a part in inflammatory arthritis more widely. And treatment runs the link the other way, since anti-inflammatory tablets for the joints can trouble the stomach. Each link is taken in turn below, sticking to what the evidence supports, and the guide then comes to the gut symptoms that need a doctor, and how soon.

Inflammatory bowel disease is the shared name for Crohn's disease and ulcerative colitis, in which the lining of the gut becomes inflamed. Joint problems are among the commonest effects they have outside the gut: up to 46 in every 100 people with Crohn's disease or colitis may have them. In some, the same inflammatory process affects the joints or the spine, a linked condition called enteropathic arthritis, which belongs to the spondyloarthritis family, alongside axial spondyloarthritis. Axial spondyloarthritis affects up to 5 in 100 people with Crohn's disease or colitis, and arthritis in the limb joints around 5 to 20 in 100.

The limb-joint arthritis comes in two broad patterns. In one, fewer than five joints are affected, usually large weight-bearing joints of the legs such as the knees, often on one side, and the joints tend to flare with the bowel, so calming the gut can settle them too. In the other, five or more joints are affected, usually in the upper body and on both sides, and the arthritis follows its own course, usually independent of the bowel, sometimes for months or years. The limb-joint forms usually do not damage the joints for good. Arthritis in the spine, axial spondyloarthritis, needs treating in its own right.

Which comes first differs from person to person. Joint problems may flare when the bowel is active, or when it is quiet, and about 7 in every 100 people with axial spondyloarthritis also develop inflammatory bowel disease. That is one reason a rheumatologist asks about bowel symptoms, and why a GP or rheumatologist refers someone with possible bowel disease to a gastroenterologist. Because one underlying disease affects two organs, treatment, which for the bowel can include medicines that damp down the immune system, such as immunosuppressants or biologics, is planned with both in view, and care is best shared between the rheumatology and gastroenterology teams.

An infection, rather than a long-term bowel disease, can also be the starting point. Reactive arthritis is joint swelling that follows an infection elsewhere in the body, and food poisoning is one of the common triggers. The joints usually become sore and swollen one to four weeks after the infection, by which time the stomach upset may have settled.

The swelling is not an infection of the joint. It comes from the immune system, stirred up by the infection and turning on the joints by mistake; the tendons around them and the eyes can be caught up too. Reactive arthritis usually goes away within six months, though it can last longer, come back, or lead to another kind of arthritis that needs long-term treatment. Since a hot, swollen joint has several possible causes, infection among them, it needs a same-day assessment, as the second list under When to seek help sets out, rather than being taken for a passing reaction.

Trillions of bacteria live in the gut. Together they are called the microbiome, and they help to keep inflammation and the immune system in balance. Because the gut's bacteria and the immune system are linked, researchers have long suspected that these bacteria may play a part in inflammatory arthritis, rheumatoid and psoriatic arthritis among them.

The work is still at the research stage. In 2021 Arthritis UK reported teams it was funding looking for the particular gut bacteria tied to inflammatory arthritis and whether some predict how well treatment works; one team had identified bacteria that turn up often in people with a genetic risk of rheumatoid arthritis, and another was following the gut bacteria of people at risk to see what changes as the disease develops. In axial spondyloarthritis, the genes that raise the risk also change the gut's bacteria, and research was funded to test whether replacing them, by a transplant of bacteria from a donor's stool, could help, a treatment Arthritis UK reports has worked in inflammatory bowel disease. None of this has yet produced a proven treatment for arthritis.

So far, probiotics have not been shown to help, and there is no evidence that changing the gut's bacteria, by diet or otherwise, alters autoimmune conditions such as rheumatoid arthritis; claims to the contrary deserve caution. Eating a varied, balanced diet does your general health good, and diet and arthritis covers the details, yet it backs up prescribed treatment and cannot stand in for it.

Coeliac disease is an immune reaction to gluten that damages the lining of the small bowel, so that the body cannot take in nutrients properly. Although it is not a type of arthritis, it can weaken the bones. When the damaged bowel absorbs too little of the calcium and other nutrients that bones need, bone density falls: low bone density, or osteoporosis, is found in between 38 and 72 in 100 people when coeliac disease is diagnosed. Once gluten is out of the diet, the bones usually recover some of their density, and a bone density scan can check them if there is concern.

One practical warning follows. Cutting out gluten yourself, hoping it will ease sore joints, can hide coeliac disease, since the blood test can give a misleading result once gluten is out of your diet. Bone or joint pain together with bowel symptoms that have yet to be explained is a fair reason to ask your GP for that blood test first.

Treatment forms the last link. Ibuprofen, naproxen and the other anti-inflammatory tablets (NSAIDs) ease stiff, painful joints for many people, but the stomach can pay a price: irritation, and with regular or long-term use a higher chance of an ulcer or a bleed.

None of this bars them; it means using them carefully. Take them with food, at the smallest dose that helps, for as short a time as you need them. If you need them for months, or your stomach is more vulnerable, a doctor will often add a medicine that reduces stomach acid, such as omeprazole. With Crohn's disease or colitis, extra care is taken with NSAIDs, which can sometimes unsettle the bowel: the NHS advises people with Crohn's disease not to take them unless a doctor recommends them, so ask before you start one. The signs of a bleed, and where to go for each, are in the lists below.

Gut and joint symptoms are both common, and often unrelated. Some gut symptoms, though, need attention in their own right, and some cannot wait, so the lists below give each its route, the most urgent first, and the paragraph after them covers what can be seen within days.

Treat any of these as a 999 or A&E emergency: call 999 and do not drive yourself to A&E.

• Severe illness with suspected sepsis: a high fever with shaking, confusion, rapid breathing, or feeling dramatically worse over hours
• With a fever or feeling unwell, a rash that does not fade when you press it, a stiff neck with eyes that cannot bear bright light, or skin, lips or tongue turning blue, grey, pale or blotchy, since these can be signs of meningitis or sepsis, as can a very bad headache, confusion or a first seizure with a fever or feeling unwell; on black or brown skin the rash and the change of colour may be easier to see on the palms of the hands or the soles of the feet
• Vomiting blood, or bleeding from the back passage that is heavy or will not stop, most of all with faintness, confusion or pain in the abdomen, or vomit that is black or dark brown, since a bowel inflamed by Crohn's disease or colitis can bleed, as can a stomach irritated by anti-inflammatory tablets
• Lips, mouth, throat or tongue that suddenly swell, a throat that feels tight, very fast breathing or a struggle to breathe or to swallow, skin, tongue or lips turning blue, grey or pale (on black or brown skin this may be easier to see on the palms of the hands or the soles of the feet), becoming suddenly very confused, drowsy or dizzy, or fainting and not being able to be woken, since this can be a severe allergic reaction, anaphylaxis, which can follow a dose of any medicine
• Severe pain in the abdomen, or vomiting poo, since a badly inflamed bowel, or one that has narrowed or become blocked, can need treatment in hospital
• An eye that suddenly and completely loses its sight

Any of these needs an assessment that is urgent, on the same day, from your GP, your rheumatology or gastroenterology team, or NHS 111:

• A fever, or feeling generally unwell, on immunosuppressant, biologic or steroid treatment, since an infection has to be treated early
• A joint that is hot and swollen, with a fever or feeling unwell, since an infected joint has to be ruled out at once, at A&E or through NHS 111
• A joint that has become hot and very swollen suddenly, or is worsening quickly, even without a fever, since an infected joint does not always announce itself with one; a joint that will take no weight at all, or that cannot be moved, is a 999 or A&E emergency, whether or not there is a fever
• Sore joints with a high temperature, or feeling hot, cold or shivery, or joint pain that paracetamol or other simple painkillers do not control, in the weeks after a stomach bug, since reactive arthritis, or an infection in a joint, has to be checked that day
• Black or dark red stools, or bloody diarrhoea, or very bad diarrhoea, or a flare of the bowel with a fever or a racing heart, or a bowel that has stopped passing wind or poo, since these have to be treated that day
• A tummy ache that will not go away, keeps coming back or is getting much worse, or one that comes with bloating that lingers or keeps returning, weight lost without trying, or diarrhoea that has not settled after a few days, since its cause has to be found; severe pain in the abdomen belongs to the first list
• Diarrhoea lasting more than a week, since a bout of diarrhoea usually stops within 5 to 7 days, and one that lasts longer needs looking into that day
• A new red, painful eye, or sight that has blurred, dimmed or changed, which needs an eye casualty or urgent eye clinic the same day, as does an eye that light hurts, since reactive arthritis and inflammatory bowel disease can both bring red, sore eyes, and inflammation inside the eye can harm the sight if it is not treated; the uveitis guide explains more
• Being near someone with measles, chickenpox or shingles, while you take a medicine that weakens the immune system, since measles and chickenpox can be dangerous when the immune system is weakened, and you can catch chickenpox from someone with shingles if you have never had chickenpox; NHS 111 can tell you what to do that day

Short of the signs in the lists above, bowel symptoms that have started recently or are creeping up, like diarrhoea that keeps coming back, blood in your poo, weight lost without trying, mouth ulcers that keep returning, or bowel treatment that has stopped working, are for your GP or your rheumatology or gastroenterology team within days. A joint that has newly become swollen, with none of the signs above, is for your GP or your team within days too, since a newly inflamed joint needs an urgent referral. No referral is needed to be seen here; next-working-day appointments can almost always be arranged, and same-day appointments are sometimes possible. If you cannot tell how urgent something is, asking is never a mistake.

Some of these links, inflammatory bowel disease and reactive arthritis among them, are firmly established; others, such as the role of gut bacteria, are still under study. Either way, symptoms in the gut and symptoms in the joints each need examining properly, not guessing at. When both are present, a rheumatologist can judge whether one explains the other, look for inflammation in the joints, and share care with a gastroenterology team where you have one, so that bowel and joints are treated as one problem where they are one.

Can a gut problem lead to arthritis?

Sometimes. A linked joint inflammation, enteropathic arthritis, can accompany Crohn's disease and ulcerative colitis, and a gut infection such as food poisoning can set off reactive arthritis, usually one to four weeks later. Either way, it is the immune system that inflames the joints by mistake; the joints themselves are not infected, though a hot, swollen joint still needs checking that day, at A&E or through NHS 111 if it comes with a fever or feeling unwell, or from your GP or NHS 111 if not, since infection has to be ruled out. Both conditions are worth having assessed in their own right.

Do gut symptoms come before joint symptoms, or after?

It varies. With Crohn's disease or colitis, joint problems may flare along with the bowel, or flare when the bowel is quiet; and about 7 in every 100 people with axial spondyloarthritis also develop inflammatory bowel disease. Reactive arthritis follows the infection that sets it off, often after the stomach upset has passed, so the link is easy to miss. Mention any bowel trouble to your rheumatologist, whether it is happening now or happened weeks ago, since it can explain what the joints are doing.

Can probiotics or a special diet treat inflammatory arthritis?

Not on the evidence so far. Probiotics have not been shown to help, and there is no evidence that changing the gut's bacteria, by diet or any other means, alters autoimmune conditions such as rheumatoid arthritis. The research on gut bacteria is promising but at an early stage. A balanced diet is good for your general health, and supports rather than replaces your prescribed treatment; the evidence on food is covered in diet and arthritis.

Is coeliac disease linked to my joints or bones?

Not as a kind of arthritis, but coeliac disease can weaken the bones: because the damaged bowel absorbs too little calcium and other nutrients, low bone density is common when it is found, and it usually improves on a gluten-free diet. Bone or joint pain that comes with bowel symptoms that have no explanation yet is a fair reason to ask your GP about a coeliac test; carry on eating gluten until the diagnosis is confirmed, since the tests rely on it.

Do anti-inflammatory tablets harm the stomach?

They can. The stomach lining is what NSAIDs, the anti-inflammatory painkillers, tend to irritate, and the longer they are taken, the higher the chance of an ulcer or a bleed. That does not rule them out: taken with food, at the lowest dose that helps and for the shortest time needed, they are widely used, and if you need them for a long time your doctor may add a medicine that cuts stomach acid, such as omeprazole. Tell your doctor before starting one if you have had a stomach ulcer or bleeding, or have Crohn's disease or colitis. Vomiting blood, or severe pain in the abdomen, is a 999 or A&E emergency, and black or dark red stools need an urgent assessment that day from your GP, your team or NHS 111, as does a stomach ache that will not go away, keeps coming back or is getting much worse; other stomach pains while taking one, short of the second list under When to seek help, are for your doctor within days.