Gum disease is four times more common in people with rheumatoid arthritis and also tends to be more severe, according to scientists.

Researchers studied 91 adults with rheumatoid arthritis and a comparison group of 93 healthy people, matched for age and sex.

All participants were non-smokers, as smoking is a known risk factor for rheumatoid arthritis. It is also strongly linked with the production of antibodies, which signals a systemic reaction to a person's own proteins (ACPAs).

None of the people with rheumatoid arthritis had been treated with arthritis drugs known as disease modifying drugs, or DMARD, for short.

The severity of the gum disease was assessed by quizzing the study participants about their symptoms.

These included swollen and bleeding gums, sensitive teeth, loose teeth, and a history of tooth loss caused by gum disease. How far the gum had receded from the surface of the tooth, known as pocketing, was also measured.

Almost two thirds of patients (just under 65%) with rheumatoid arthritis had evidence of gum disease, compared with just over one in four (28%) of their healthy peers.

Overall, patients with rheumatoid arthritis were four times as likely to have gum disease. And their gum disease also tended to be more severe.

The depth of pocketing was also significantly greater among those with rheumatoid arthritis and especially among those who tested positive for ACPA, compared with those in the healthy group.

Those who tested positive for ACPA had had their rheumatoid arthritis for longer, had higher levels of disease activity, and higher levels of inflammation than those who tested negative.

Porphyromonas gingivalis is one of the main bacteria behind gum disease, and it is also the only organism known to produce an enzyme capable of generating ACPA in gum tissue.

Even those with rheumatoid arthritis, but without serious gum disease, as measured by pocketing, had symptoms, such as bleeding and swollen gums and sensitive teeth, but tooth loss was seen only in those with serious gum disease.

But mild gum disease in patients with rheumatoid arthritis may become more serious, and include testing positive for ACPA, suggest the authors. Published research indicates that ACPA antibody levels increase the longer a person has had rheumatoid arthritis.

The study was published online in the Annals of the Rheumatic Diseases.

Rheumatoid arthritis is a long-term disease that leads to inflammation of the joints and surrounding tissues. It can also affect other organs.bIts cause is unknown and it is an autoimmune disease, which means the body's immune system mistakenly attacks healthy tissue.

The condition usually occurs in middle age and is more common among women.