EXTENDED REPORT

¹ Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden
² Rheumatology Unit, Department of Medicine, Karolinska University Hospital, Stockholm
³ Department of Public Health Sciences, Karolinska Institutet, Stockholm

Correspondence to:
Camilla Bengtsson
Institute of Environmental Medicine, Box 210, Karolinska Institutet, SE-171 77 Stockholm, Sweden; camilla.bengtsson{at}imm.ki.se

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.

Abbreviations: ACR, American College of Rheumatology; EIRA, Epidemiological Investigation of Rheumatoid Arthritis; FoB, Folk-och bostadsräkning (Swedish census); ISCED, International Standard for Classification System of Education; NYK, Nordisk yrkesklassificering (Swedish classification system of occupations); RF, rheumatoid factor; RR, relative risk; SUN, Svensk utbildningsnomenklatur (Swedish classification system of education)

Keywords: socioeconomic status; rheumatoid arthritis; formal education; social class

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