To evaluate exposure to external factors associated with risk or prevention of rheumatoid arthritis (RA).
Two hundred and ninety-three incident cases of RA and 1346 population-based referents were included in a case-referent study, in which previous exposure experiences were collected through a postal questionnaire.
An inverse association between RA and additional schooling after compulsory school was seen for men. Current smoking was associated with significantly increased risks of RA for men and women [odds ratio (OR) 2.9, 95% confidence interval (CI) 1.4-6.4, and OR 1.8, 95% CI 1.1-2.9, respectively], as was previous smoking for men (OR 2.3, 95% CI 1.2-4.4). There were also indications of relationships between previous use of a private well and RA in both men and women.
Several previously published associations have been reproduced in the present study, which also generates some new hypotheses that suggest further research.