The current thinking is that rheumatoid arthritis (RA) occurs when genetic and environmental factors combine to trigger immunopathological changes that lead to an inflammatory arthritis.
Cigarette smoking is the one environmental factor with an unequivocal association. The impact seems to be limited to patients with seropositive disease, and its influence is greater in men compared to women.
Other strong associations include low alcohol use (alcohol is protective) and periodontitis (increased risk in edentulous patients and those with periodontal disease).
Weaker environmental risk factors include vitamin D intake (protective), obesity (increases risk), social status (socioeconomic status and education are inversely associated with risk of developing RA), breast-feeding (protects mother), and high birth weight (higher risk).
There are contradictory reports in the literature about the association of oral contraceptive pill use and history of blood transfusions, with some finding protective effects and others finding an increased risk.