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Rheumatoid arthritis
Original article
Physical workload is associated with increased risk of rheumatoid arthritis: results from a Swedish population-based case–control study
  1. Pingling Zeng1,2,
  2. Lars Klareskog2,
  3. Lars Alfredsson1,3 and
  4. Camilla Bengtsson1
  1. 1Institute of Environmental Medicine, Karolinska Institute, Stockholm, Sweden
  2. 2Rheumatology Unit, Department of Medicine at Karolinska University Hospital, Karolinska Institute, Stockholm, Sweden
  3. 3Center for Occupational and Environmental Medicine, Stockholm County Council, Stockholm, Sweden
  1. Correspondence to Dr Pingling Zeng; pingling.zeng{at}ki.se

Abstract

Objectives This study investigated: (1) the association of physical workload (PW) and risk of rheumatoid arthritis (RA); (2) the potential interactions between PW and the genes in the human leucocyte antigen (HLA) region.

Methods A population-based case–control study involving incident cases of RA (3150 cases and 5130 controls) was performed using data from the Swedish Epidemiological Investigation of Rheumatoid Arthritis. Information on 7 types of self-reported PW exposure and HLA-DRB1 genotypes of cases and controls were gathered. Anticitrullinated protein antibody (ACPA) status of cases was identified. For each PW exposures, exposed participants were compared with unexposed participants. ORs with 95% CIs of RA (overall), ACPA-positive RA and ACPA-negative RA associated with different PWs were estimated using logistic regression. HLA-PW interactions were estimated using the principle of departure from additivity of effects by calculating attributable proportion (AP) due to interaction.

Results ORs of developing RA associated with 6 various PW exposures ranging from 1.3 (95% CI 1.1 to 1.4) to 1.8 (95% CI 1.6 to 2.0) were observed. Exposure to more types of PW was associated with increasing risk for RA (p<0.0001). No major difference in the ORs between ACPA-positive and ACPA-negative RA was found. For some exposures, we found evidence of interactions between PW and the HLA-DRB1 shared epitope genes, regarding risk of ACPA-positive RA (AP: from 0.3 (95% CI 0.1 to 0.5) to 0.4 (95% CI 0.2 to 0.6)).

Conclusions PW is associated with the risk of ACPA-positive and ACPA-negative RA. Interactions between PW and the HLA-DRB1 shared epitope were found in ACPA-positive RA.

  • Rheumatoid Arthritis
  • Epidemiology
  • Ant-CCP

This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/

https://doi.org/10.1136/rmdopen-2016-000324

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    Footnotes

    • Contributors PZ carried out data analysis, created the tables and wrote the manuscript. CB initiated the study, provided supervision in data analysis and revised the manuscript. LA and LK are principal investigators of the EIRA study and have been involved in study conception and design, acquisition of data, analysis and interpretation of data as well as manuscript revision.

    • Funding Vetenskapsrådet, European Union-funded Innovative Medicines Initiative (BTCure), Working Life and Welfare, Swedish Rheumatism Foundation, OSTEOIMMUNE, Stiftelsen Konung Gustaf V:s Jubileumsfond, AFA Försäkring, VINNOVA.

    • Competing interests None declared.

    • Patient consent Obtained.

    • Ethics approval Ethics committee of the Karolinska Institute.

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Data sharing statement No additional data are available.