Socioeconomic status and the risk of developing rheumatoid arthritis: results from the Swedish EIRA study

OBJECTIVE: To study whether formal education and occupational class are associated with incidence of rheumatoid arthritis overall and with the incidence of the two major subgroups of rheumatoid arthritis-seropositive (RF+) and seronegative (RF-) disease. METHODS: 930 cases and 1126 controls participated in a population based case-control study using incident cases of rheumatoid arthritis, carried out in Sweden during the period May 1996 to June 2001. The relative risk (RR) of developing rheumatoid arthritis with 95% confidence interval (CI) was calculated for different levels of formal education compared with university degree and for different occupational classes compared with higher non-manual employees. RESULTS: SUBJECTS: without a university degree had an increased risk of rheumatoid arthritis compared with those with a university degree (RR = 1.4 (95% CI, 1.2 to 1.8)). For manual employees, assistant and intermediate non-manual employees together, the risk of developing rheumatoid arthritis was about 20% more than for non-manual employees. These increased risks were more pronounced for RF+ than for RF- rheumatoid arthritis and were mainly confined to women. Smoking could not of its own explain the observed associations between risk of rheumatoid arthritis in different socioeconomic groups in Sweden. CONCLUSIONS: There was an association between high socioeconomic status and lower risk of rheumatoid arthritis in a population based investigation that was representative for the Swedish population. The study shows that as yet unexplained environmental or lifestyle factors, or both, influence the risk of rheumatoid arthritis, even in the relatively egalitarian Swedish society.