Background Airborne agents are considered important environmental triggers of rheumatoid arthritis (RA) among genetically susceptible individuals. Due to the known association between silica dust and RA, we wanted to study the association between RA and another silicate mineral; asbestos.
Objectives The aim of this study was to estimate the risk of RA from ever occupational asbestos exposure as well as years with exposure among men and women.
Methods The study base consisted of men and women living in Sweden from 1968 until 2012. RA patients were identified from the National Patient Register, the Swedish Rheumatology Register (SRQ), the Swedish population-based case-control study EIRA or the Swedish Prescribed Drug Register. We matched ten controls from the national population register per case on age, county and sex. Data on occupational histories were collected from the national population and housing censuses carried out in 1960, 1970, 1975, 1980 and 1990. A job-exposure matrix (JEM) containing historical exposure estimates from 1955–1995 to asbestos was applied to the study participants' occupational histories.
We used unconditional logistic regression to assess the odds ratios (ORs) and 95% confidence intervals (CIs) of RA associated with ever exposure and years of exposure to asbestos. ORs were adjusted for ever exposure to silica dust, which was also generated from a JEM. One of the data sources (EIRA) contained self-reported information on potential confounders. Analyses on this data source were carried out to estimate the confounding effect from pack-years of cigarette smoking and alcohol use.
Results 167 143 cases and 1 701 200 controls were included in the analysis. The proportion of participants who had ever worked with asbestos was 38% among male cases, 35% among male controls, 3% among female cases and 3% among female controls.
Ever vs. never asbestos exposure resulted in an OR of 1.15 (95% CI: 1.13–1.17) among men and 1.00 (95% CI: 0.96–1.04) among women. The ORs decreased to 1.09 (95% CI: 1.07–1.12) and 1.00 (95% CI: 0.96–1.04) for men and women respectively after adjusting for silica exposure. Asbestos exposed men were more likely than women to have worked with asbestos for a longer period of time, but the risk of RA did not appear to increase with years with the exposure. Male participants with 30 or more years of asbestos exposure at work had an OR of 1.10 (1.02–1.19) after adjustment for silica exposure.
1,882 male and 4,107 female study participants belonged to the EIRA study and had complete information on potential confounding factors. The OR among men went from 1.61 (95% CI: 1.32–1.97) to 1.35 (95% CI: 1.08–1.70) when we additionally adjusted for silica exposure, pack-years of smoking and alcohol use. Among women the OR went from 1.34 (95% CI: 0.93–1.93) to 1.07 (95% CI: 0.73–1.57). Risks were higher for the ACPA- RA subtype, with adjusted ORs of 1.63 (95% CI: 1.18–2.24) for men and 1.14 (95% CI: 0.66–1.98) for women.
Conclusions Asbestos exposure is associated with RA among men, and mainly the ACPA- RA subtype. The increased risk remained after adjustments for potential confounders.
Disclosure of Interest None declared