Gut Health and Rheumatoid Arthritis (RA)

Medically Reviewed by Melinda Ratini, MS, DO on March 29, 2022
7 min read

Rheumatoid arthritis (RA) happens when the immune system attacks healthy tissue in your joints. You might not expect a disease of your immune system and joints to have much to do with what’s happening in your digestive system. But it turns out, many studies show a link between RA and the health of your gut.

This link has less to do with you and more to do with the trillions of single-celled microbes – mostly bacteria – that live in your gut. Most of these bacteria are in your small and large intestines. Scientists call this collection of microbes the gut microbiome.

You’re probably used to thinking about bacteria and other microbes in a bad way. “Bad” bacteria do cause infections. You may use disinfectants to get them out of your home and take antibiotics to get rid of them when you are sick. But most microbes don’t do us any harm. Many of them actually help in different ways.

Each person has a slightly different set of microbes living in their guts. You get them to begin with at birth. Later, the microbes you have will depend on where you live, what you do, whether you take antibiotics, and what you eat. Some of your microbes will be good and others not so good. The key is to have a healthy balance.

The makeup of your gut microbiome affects how your body breaks down and uses food. Your gut microbes break down toxins and make vitamins. The microbiome in your gut also has an important role in your immune system. When you’re healthy, any microbes that might make you sick will be kept in check by others that won’t cause you any problems. If your microbiome is out of whack, it can lead to problems in your gut and in other parts of your body. Many conditions such as inflammatory bowel disease (IBD) and obesity have links to imbalances in the gut microbiome.

Doctors don’t know exactly what starts rheumatoid arthritis (RA). Most likely there are many factors that trigger it and increase RA risk. A lot of things you might read about RA probably won’t even mention your gut health or the microbiome. But there’s now evidence that it’s one of many factors.

Studies in animals were the first to suggest a link. That led researchers to look at samples from people who are healthy compared to people with RA or another type of arthritis. Some of the people with RA had gotten it recently and hadn’t treated it yet. Others had had it for a long time. They wanted to see if they could find clear differences in the gut microbiomes between people in these different groups.

It turned out that they could. About 75% of people with a new case of RA had one particular bacteria in their gut. It’s called Prevotella copri. Among those who’d had RA longer and were treating it, only 12% had P. copri in their guts. Many healthy people and those with psoriatic arthritis also had this bacteria in their guts. But the findings showed it was a lot more common to have this if you’d recently gotten RA.

They also found that people with more P. copri had less of other healthy bacteria in a group called Bacteroides. When they put P. copri into the guts of mice that already had gut inflammation, it made things worse. This bacterium also had a way of taking over in the gut. That finding in mice suggested that P. copri might have something to do with inflammation in the gut, but also in the rest of the body. Other studies since have backed up the idea that the presence of this bacteria in the microbiome might make RA more likely.

Another study soon after looked at microbes in the mouth and gut in RA. Again, they found changes in the microbiome in people with RA compared to healthy people. They also found that the imbalance of microbes partly went away in people treated for RA. People with RA had less bacteria from a group called Haemophilus in their guts and mouth and on their teeth. They also had more of another bacteria called Lactobacillus salivarius.

Yet another study showed that people with RA had fewer types of microbes in their guts. In other words, their gut microbiomes were less diverse overall. They also had more bacteria in groups called Collinsella and Eggerthella.

So different studies support the idea that the microbiome looks different in people with RA versus those without. While the details vary, many studies suggest that changes in the gut microbiome are linked to a person’s chances of getting RA. It’s possible that this is where it all starts. But it’s hard to prove, especially in people, that a shifting microbiome actually causes RA. It could be that these two things tend to happen together for some other reason.

The intestines aren't the only place where you find many bacteria. They also have more immune cells than any other part of the body. Scientists sometimes consider them to be the body’s biggest immune organs. What happens in the gut between microbes and the immune system can set the body up for a healthy immune system or autoimmune diseases, including RA.

Some people are probably more likely to have this happen than other people for reasons unrelated to their gut health and microbiome. But there’s good evidence that changes in the microbiome can ramp up certain immune cells and trigger the inflammation that goes with RA.

Some early studies hinted that common RA treatments might change the microbiome in ways that could make it healthier. Some more recent studies have looked at this more closely.

Many of the drugs used to treat RA act on the immune system in different ways. Some of them also are known to kill bacteria. So while it’s not the main reason they’re used for RA, they could affect the makeup of the microbiome. For example, there’s evidence that the drug methotrexate that’s often used for RA pushes the gut microbiome closer to a normal, healthy state.

A recent study in China followed changes in gut bacteria over time in 22 people treated for RA in two different ways. The study showed RA patients differed from people without RA in about 60 types of bacteria to start with. They had more of some and less of others. One of the treatments they looked at led to changes in 11 microbes while the other changed four. While there’s more to learn, newer biologic drugs used for RA also may change the diversity of microbes in the gut. More study is needed to know exactly how these changes affect RA and whether it might work to target the gut microbiome more specifically to treat RA better or prevent it in the future.

Your microbiome also might affect how you’ll do with treatment, according to at least one study. Researchers looked at the gut microbiome of patients before treatment. They found that the microbiomes of those who got better with treatment looked different to start with than the microbiomes of those who didn’t respond to the treatment as well.

The researcher went on to show that a computer could use information about the gut microbiome to predict whether a person with RA would get better with treatment or not. The findings suggest it may one day be possible to use microbiome tests to help make treatment decisions.

Your gut microbiome depends on what you eat. The amount of fiber in your diet is a big factor. Some types of dietary fiber have to get broken down by microbes. Otherwise we can’t digest them. Foods with lots of this type of fiber sometimes are called prebiotics. That’s because they feed good bacteria in your microbiome. Those good bacteria can help to crowd bad ones out.

Some supplements you can buy have prebiotics in them. Remember that supplements aren’t regulated in the same way as medicines. You can get this type of fiber in lots of healthy foods including:

  • Garlic
  • Onions
  • Bananas
  • Seaweed

Any diet with plenty of fruits, vegetables, beans, and whole grains will help support a healthy gut and gut microbiome.

Another way to change your microbiome is with probiotic foods or supplements. These have healthy microbes in them. Some examples of microbes (bacteria or yeast) in probiotic supplements are:

  • Lactobacillus
  • Bifidobacterium
  • Streptococci
  • Saccharomyces boulardii

Some common probiotic foods include:

  • Yogurt
  • Kombucha
  • Fermented vegetables
  • Miso

So it’s possible to change your microbiome in ways that might help your arthritis. But more study is still needed. There’s no probiotic that’s proven for RA.

One small study did show that taking a supplement with a type of Lactobacillus for 8 weeks lowered inflammation and RA activity. Another study showed benefits of Bacillus coagulans for RA. The probiotic helped with pain and signs of inflammation. But one study that looked over 12 weeks showed that people taking a probiotic said they felt better even though their RA hadn’t improved.

In general, doctors aren’t sure how much probiotic supplements or certain foods help with RA. But they are pretty safe to try for most people and might help you feel better. Some experts think that the gut and gut microbiome are promising targets for future RA medicines. If you want to try probiotics for your RA, ask your doctor first, especially if you have a weakened immune system or some other serious condition.