Researchers found similar levels of mouth bacteria in both people with the disease, and those at risk of it, who already had joint pain and high levels of antibodies which attack healthy joints.
During their study, scientists looked at 50 people with rheumatoid arthritis and 50 with inflammatory joint pain. (Stock image)
Compared to healthy people, both groups had higher saliva levels of Prevotella – some strains of which have been found to cause chronic inflammation similar to that seen in people with rheumatoid arthritis.
They also had higher levels of a type of microbe called Veilonella in their saliva and on their tongues, when compared to the balance of other bacteria in their mouths.
The arthritis patients in the study had all been diagnosed within the previous year, and it is possible that the condition disrupts bacteria in the mouth.
However experts suspect it is more likely that poor tooth-brushing allows harmful bacteria to flourish and to get into the bloodstream, causing inflammation which may help to trigger rheumatoid arthritis.