For many years it has been known that people with rheumatoid arthritis (RA) are likely to also suffer from periodontitis, a gum disease in which inflammation damages the soft tissue and bones that support the teeth. But until recently, researchers have not been able to find the link between the two diseases.
A study published in late 2016 in Science Translational Medicine suggests an answer. It found that the oral bacteria that cause periodontitis may be a trigger in developing RA. This finding underscores the importance of oral hygiene, as periodontitis is a preventable disease. It starts when bacteria build up in plaque on teeth and then cause chronic inflammation of the gums.
The missing link between RA and periodontitis appears to be a bacterium called Aggregatibacter actinomycetemcomitans (Aa) that can be found in the gums of patients with periodontitis. This bacterium induces hypercitrullination, an abnormal buildup of certain proteins that activates the immune system, inducing the chronic inflammation that damages joints as well as the soft tissue and bones in the mouth. The investigation, a collaboration among John Hopkins University, the National Institutes of Health, and the National Institute of Dental and Craniofacial Research, found that 47 percent of patients with chronic RA had the Aa bacterium in their blood, compared with only 11 percent of a non-RA control group.
Correlation, of course, does not prove causality. The researchers cautioned that their findings need to be replicated in different patient cohorts, as well as in studies on animals. These further studies may confirm the link, as well as determine whether Aa triggers RA or just worsens it once it’s already established.