Occupational Exposures Increase Rheumatoid Arthritis Risk

Lara C. Pullen, PhD

August 10, 2017

Patients with occupations that involve exposure to potentially noxious agents appear to be at an increased risk of developing both anti-citrullinated protein antibody (ACPA)+ or ACPA rheumatoid arthritis (RA). The researchers suggest that occupational status may be an important clinical factor in both diagnosing RA and estimating the risk for RA.

The investigators analyzed 3522 cases and 5580 controls from the Swedish population-based Epidemiological Investigation of Rheumatoid Arthritis case-control study. Anna Ilar, MSc, a graduate student at the Karolinska Institutet, Stockholm, Sweden, and colleagues identified occupational exposure as a dominant risk factor for RA after adjusting for previously known risk factors such as cigarette pack-years, alcohol use, body mass index, and education. The report was published online August 10 in Arthritis Care & Research.

"Previous studies have not considered these lifestyle-related risk factors to the same extent. Our findings therefore indicate that work-related factors, such as airborne harmful exposures, may contribute to disease development," said Ilar in a news release. "It is important that findings on preventable risk factors are spread to employees, employers, and decision-makers in order to prevent disease by reducing or eliminating known risk factors," she added.

Environment Exposures and RA

The study focused on the influence of environment on the risk of developing RA. The researchers collected exposure information retrospectively, however, and acknowledge that this allowed for the possibility of misclassification of work history and other factors.

The researchers evaluated the incidence of RA in 76 occupational groups. They used the incidence of RA in 12 occupational groups belonging to the professional areas of "professional, technical and related work" and "administrative, managerial, and clerical work" as reference groups in all analyses. The investigators used these occupational groups as reference groups because researchers had previously reported that these occupations are not associated with an increased risk for RA.

Four occupational groups were associated with ACPA+ or ACPA RA: electrical and electronics workers, bricklayers and concrete workers, material handling operators, and assistant nurses and attendants. In particular, male workers in the manufacturing sector had a higher risk of developing ACPA+ RA than workers within the professional, administrative, and technical sectors: bricklayers and concrete workers (odds ratio [OR], 2.9; 95% confidence interval [CI], 1.4 - 5.7), material handling operators (OR, 2.4; 95% CI, 1.3 - 4.4), and electrical and electronics workers (OR, 2.1; 95% CI, 1.1 - 3.8). When the investigators performed the same analysis for ACPA RA in male workers, they found two types of workers were at increased risk: bricklayers and concrete workers (OR, 2.4; 95% CI, 1.0 - 5.7) and electrical and electronics workers (OR, 2.6; 95% CI, 1.3 - 5.0).

Among women workers, assistant nurses and attendants had a slightly increased risk for ACPA+ RA relative to workers within the professional, administrative, and technical sectors (OR, 1.3; 95% CI, 1.1 - 1.6). None of the occupations was significantly associated with ACPA RA in women workers.

Although other occupational groups initially appeared to be associated with RA, the association disappeared after the researchers adjusted for the known confounders.

Noxious Agents and Innate Immunity

The findings suggest that work-related factors may contribute to the pathogenesis of RA. The investigators note that all the identified occupations are associated with exposure to a mixture of different, primarily airborne, noxious agents. Possible exposures include silica, asbestos, organic solvents, and motor exhaust.

The authors propose a biological mechanism by which these chemicals could promote the development of RA. Specifically, they hypothesize that these noxious agents may activate innate immunity via their effects on toll-like receptors and other pattern recognition receptors. This would then trigger an autoimmune response in susceptible individuals.

The authors have disclosed no relevant financial relationships.

Arthritis Care Res. Published online August 10, 2017. Full text

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