Circular link between gum disease and rheumatoid arthritis revealed in new study

From birmingham.ac.uk

Association between periodontitis and rheumatoid arthritis is long established, but which comes first has long been debated by scientists 

Researchers have uncovered compelling evidence of a two-way relationship between rheumatoid arthritis (RA) and periodontitis (gum disease), showing that treating gum disease can significantly reduce inflammation and improve RA symptoms for patients.

The study, published in the Journal of Clinical Periodontology, examined how microbial imbalances in the mouth – known as dysbiosis – contribute to systemic inflammation in RA patients.

Led by University of Birmingham researchers from the Periodontal Research Group and the National Institute for Health and Care Research (NIHR) Birmingham Biomedical Research Centre, the University of Michigan and Queen Mary University of London, the study investigated the interactions between oral bacteria and immune molecules, and correlated the molecular interactions with clinical outcomes in 159 participants, including RA patients with and without gum disease, individuals with gum disease alone, and healthy controls.

"We found that treating gum disease through intensive periodontal therapy broke this cycle: it improved RA activity scores, reduced antibodies to oral pathogens, and re-established a balanced interaction between oral microbes and the immune system within three months."

Professor Iain Chapple, University of Birmingham

Key Findings

• RA patients exhibited distinct oral microbiomes, even before gum disease developed. These microbial communities were richer and more diverse than those in healthy individuals and formed dense interaction networks.

• Certain bacteria, such as Cryptobacterium curtum and Prevotella species, were strongly associated with RA and correlated with pro-inflammatory cytokines.

• RA patients had higher levels of antibodies against oral pathogens, particularly Porphyromonas gingivalis, a bacterium linked to protein citrullination – a process implicated in RA autoimmunity.

• Severity of gum disease strongly correlated with RA activity scores, including joint swelling and pain.

Professor Iain Chapple, co-lead for the oral, intestinal and systemic health theme of Birmingham’s NIHR Biomedical Research Centre, said:

“These findings are extremely significant, as it’s the first time that rheumatoid arthritis (RA) and periodontitis (gum disease) have been shown to be linked in a circular relationship, creating a vicious cycle of inflammation. RA-driven systemic inflammation disrupts the oral microbiome, fostering harmful bacteria that trigger gum disease; in turn, these bacteria worsen oral inflammation and impair immune responses, which in turn fuel RA by generating antibodies linked to joint damage.

“We found that treating gum disease through intensive periodontal therapy broke this cycle: it improved RA activity scores, reduced antibodies to oral pathogens, and re-established a balanced interaction between oral microbes and the immune system within three months.”

Professor Purnima Kumar, senior author and Chair of the Department of Periodontics and Oral Medicine at the University of Michigan said: “Oral health is the result of an evolutionary balance between the resident oral bacteria and the mucosal immune system. We discovered that RA disrupts this microbial-mucosal interaction, leading to a self-perpetuating cycle of inflammation and dysbiosis.

“When we treat periodontitis, we reboot these molecular interaction networks, thereby moving the oral ecosystem towards balance and disrupting the cycle of systemic inflammation. This is yet another reminder that the body functions as an integrated biological system, and therefore, therapeutic interventions need to be integrated to be effective.

The importance of integrated care

RA is a leading cause of disability in the UK, affecting around 1% of the population; whilst gum disease is widespread and often overlooked in systemic health management. This research highlights the importance of integrated care to improve the overall health and wellbeing of patients navigating inflammation.

The study also evaluated the impact of intensive non-surgical periodontal therapy – professional cleaning combined with oral hygiene coaching – compared to oral hygiene advice alone:

• Periodontal treatment reduced gum inflammation and restored balance between oral bacteria and the immune system.

• Levels of inflammatory cytokines in gum fluid dropped significantly after treatment.

• Circulating antibodies to oral bacteria decreased, and RA clinical scores improved, including reductions in joint tenderness and disease activity.

• Network analysis showed that therapy “re-wired” immune–microbial interactions, strengthening the body’s ability to control harmful bacteria.

Dr Isabel Lopez-Oliva, a NIHR Academic Clinical Lecturer from Queen Mary University of London and a co-author of the study, added: “We’ve demonstrated that periodontal therapy offers measurable benefits for RA patients, even when the disease is established. This opens the door to new strategies for reducing inflammation and improving quality of life.”

The research was supported by the National Institute of Dental and Craniofacial Research and delivered through the National Institute for Health and Care Research (NIHR) Birmingham Biomedical Research Centre (BRC), which brings together multidisciplinary research teams specialising in a wide range of inflammatory conditions – including inflammatory arthritis and periodontitis. The study builds on previous work from the OPERA trial, which first suggested that periodontal treatment could improve RA outcomes.

https://www.birmingham.ac.uk/news/2026/circular-link-between-gum-disease-and-rheumatoid-arthritis-revealed-in-new-study