Two questionnaire-based case-referent studies were performed to primarily assess the impact from occupational and environmental exposures on the aetiology of rheumatoid arthritis (RA). The two studies included prevalent and incident cases of RA, respectively. All determinants were evaluated separately for the two materials, and potential occupational risk factors were also analysed after pooling of the two studies. Most associations found between occupational exposures and RA regarded men. Increased risks for RA were seen for exposure to asphalt (OR 6.0, 95% CI 1.6-27.7), vibrations (OR 2.1, 95% CI 1.4-3.3), crops and/or forage (OR 2.0, 95% CI 1.3-3.0), mineral dust (OR 1.8, 95 % CI 1.0-3.2). and mineral oil (OR 1.5, 95 % CI 1.0-2.3 ), with dose-response relationships between RA and exposure to mineral dust and vibrations. Occupational categories at increased risk of RA among men were conductors, freight and transport workers (OR 4.6, 95 % CI 1.4-15.0), pulp and paper workers (OR 3.9, 95 % CI 1.2-12.8), and farmers (OR 2.3, 95 % CI 1.4-3.5). Regarding women, increased risks for RA were seen for exposure to meat (OR 2.2, 95 % CI 1.0-4.9), hairdressing chemicals (OR 1.7, 95 % CI 0.7-4.5), and for hairdressers (OR 1.7, 95 % CI 0.7-4.0). The results refer to the pooled material.
Regarding leisure-time activities, an increased risk was seen for mineral oil exposure among men in the study with incident cases (OR 2.0, 95 % CI 0. 7-6.2 ). In this study, an association was also seen for men for having ever used a private well (OR 1.5, 95 % CI 0.8-2.9). In the study with prevalent cases, associations were seen for both sexes for having been exposed to water from a private well at time of birth (OR 1.5, 95 % CI 0.9-2.4 for women, and OR 2.8, 95 % CI 1.5-5.2 for men). The risk of RA was increased for men with previous exposure to mould indoors (OR 4.6, 95 % CI 1,1-20.2 ), and an association was also seen for long time use of hair dyes and/or bleach among women (OR 1.9, 95 % CI 0.8-4.5). In the study with incident cases, the risk for RA was increased among men with previous use of skin lotion (OR 3.0, 95 % CI 0.9-9.8).
For both sexes, increased risks for RA were seen for current and previous smoking, with even higher ORs for seropositive cases among men. In the study with incident cases, male subjects with more than 20 pack years of smoking had an OR of 2.5 (95 % CI 1.2-5.1), corresponding to an OR of 1.6 (95% CI 0.9-3.1) among women. There was a tendency towards increasing risks with increasing number of pack years for men in both studies, with significant tests for trend in the study with prevalent cases. For both sexes, higher schooling resulted in a decreased risk for RA.
The relationship between RA and allergy was evaluated more extensively in a cross-sectional study, and negative associations between RA and certain manifestations of hay fever were found. An almost significantly decreased risk for allergy was found in the study with prevalent cases with both sexes included in the analysis (OR 0.6, 95 % CI 0.4-1.0). Regarding other comorbidity, there were positive associations between RA and self-repotted thyroid conditions (OR 3.5. 95 % CI 1.1-10.8) and previous treatment with insulin (OR 10.2, 95 % CI 1.7-60.8) among women in the study with prevalent cases. In the cross-sectional study, there was an association between RA and diabetes (OR 2.8. 95 & CI 0.9-8.9), with both sexes included in the analysis. Associations were seen between previous joint trauma and RA for women in both case-referent studies (OR 2.5, 95 % CI 1.0-6.6 in the study with prevalent cases) as well as for men in the study with incident cases (OR 2.2, 95% CI 0.6-7.1).
Altogether, the determinants conveying the risk for RA differ between sexes. RA is a condition most often affecting women. but the present studies, as well as previous research, have established that most extemal factors evaluated so far seem to be of more importance for men than women.
Linköping: Linköpings universitet , 2003. , 94 p.
2003-10-09, Aulan, Hälsans hus, Universitetssjukhuset, Linköping, 09:00 (Swedish)