Ankylosing spondylitis (AS) is a rare type of inflammatory arthritis that primarily affects the spine, lower back, and sacroiliac joints. The condition can cause new bone growth, pain, and swelling.

Researchers have identified a connection between AS and the bacteria in the gut. Evidence suggests that certain bacteria can trigger AS, while other types may not.

Hear from an expert about the connection between AS and gut health, as well as ongoing research in the area.

While researchers do not exactly know what causes AS, they have identified that certain genes increase the risk of developing the condition.

A person with the HLA-B27 gene is 100 times more likely to develop AS than a person who does not have this genetic marker. Scientists have also discovered that this genetic trait may interact with the gut microbiome.

Just having the HLA-B27 gene does not necessarily mean a person will have AS. Moreover, a person who does not have the marker can still develop the condition.

This is why scientists believe that there are other potential genes involved in the development of AS, as well as non-genetic triggers, such as bacteria.

The human body is home to trillions of bacterial cells. There are two to three times the amount of bacterial cells in a person’s body than human cells. Everyone carries different amounts and types of bacteria. Many of these live in the digestive tract, making up a person’s gut microbiome.

Dr. Joseph Martinez, a board-certified rheumatologist with Texas Orthopedics in Austin, believes the link between the gut and AS may lie within the microbiome.

“The microbiome — that is, the usual microorganisms that live in our digestive tract — may play a role in the development of AS. There are mouse studies and ongoing human studies that seem to show a link between the microbiome and the development and progression of inflammatory arthritis, to include AS,” said Dr. Martinez.

According to some experts, the bacteria that humans share their bodies with have major effects on the immune system.

Some scientists have found that certain bacteria present in the intestines pass into the bloodstream when the defenses of the intestines break down, triggering an immune response that could play a role in AS.

The gut bacteria and resulting immune system reactions that trigger AS may also play a part in causing Crohn’s disease and ulcerative colitis, which are inflammatory bowel diseases (IBDs).

Research shows that 6–14% of people with AS have IBD, which is a far greater percentage than in the general population.

The reverse is also true. According to the Crohn’s and Colitis Foundation, AS affects 2–3% of people with IBD.

For reference, the Spondylitis Association of America (SAA) note the percentage of people with AS in populations around the world varies, with the lowest — 0.02% — in people in sub-Saharan Africa, and a higher — 0.35% — in the Northern Arctic.

Scientists are currently using their knowledge of the link between the gut and AS to develop new treatments.

Dr. Martinez pointed out: “Potential treatment avenues exploring the gut-joint axis are an active area of research at this time. Rifaximin has undergone preliminary research in animal models, which shows promising effects on the progression of AS, but this still requires further studies [to examine whether] this will have any benefits in humans.”

There are treatment options available that can help a person with AS manage their symptoms and slow the progression of the disease. These options include a combination of:

  • medication
  • exercise
  • physical therapy with a focus on maintaining proper posture

Medications for AS include:

  • nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, to manage pain and swelling
  • tumor necrosis factor inhibitors, such as adalimumab (Humira), etanercept (Enbrel), and golimumab (Simponi, Simponi Aria)
  • interleukin 17 inhibitors, such as secukinumab (Cosentyx) and ixekizumab (Taltz)

All of these medications have a risk of side effects. Some of them, particularly NSAIDs, can negatively affect gut health.

Some evidence suggests that Lactobacillus, a “friendly” type of bacteria that live in the gut, may help treat various diseases.

These bacteria, also known as probiotics, are often an ingredient of yogurt. They help both break down food and fight off harmful bacteria that can cause disease.

According to the SAA, scientists have treated various diseases in mice, including colitis, by feeding mice specific bacteria or products from these bacteria.

When scientists gave antibiotics to rats with the HLA-B27 marker, the arthritis in the rats decreased. When the scientists fed the rats Lactobacillus, the rats stayed in remission.

Research suggests that probiotics such as Lactobacillus may be effective in slowing the progression of AS when used in conjunction with other therapies. Taking Lactobacillus can also help relieve symptoms of IBD, which many people with AS have.

However, Dr. Martinez cautioned that “the potential benefits of supplements and diet in ankylosing spondylitis are unclear; more studies are needed on this matter.”

Researchers have established a link between AS and the gut microbiome. Certain types of bacteria that live in the digestive tract may trigger the development of AS. Scientists are currently researching the connection to find better treatment options.