Quitting smoking can benefit people who suffer from rheumatoid arthritis, a new study finds.

About 1.5 million people in the U.S. have rheumatoid arthritis (RA), an autoimmune disorder that attacks the tissue around the body’s joints and also can widespread cause pain and disability.

It is widely recognized that cigarette smoking is a strong risk factor for the development of RA but the relationship between smoking and disease activity in established disease has been less clear.

In this new study, researchers at Stamford University in Palo Alto, Calif. looked at factors found in RA, including expressions of inflammation, called cytokines, as well as other clinical measures of rheumatoid arthritis disease activity in  U.S.Veterans and compared them with those of non-smokers and never-smokers.

The team studied 1,466 U.S. veterans enrolled in the Veterans Affairs RA registry, and enrolled 1,130 (76 percent) whom tested positive for anti-CCP2 antibodies, which is a marker for the disease. Of the participants, 89 percent were men, and the study involved   321 current smokers, 599  former smokers, and 210 never smokers.

The researchers found that cigarette smoking increased the expression of markers of inflammation as well as clinical measures of disease activity.  But they also found that stopping smoking eventually reduced the level of inflammatory markers and decreased disease activity similar to levels observed in never smokers.

This study is the first to demonstrate meaningful differences in such factors corresponded to a reduced level of disease activity, the researchers say of their findings, which appears online in Rheumatology.