Working in a cold environment (WCE), whether outdoors or indoors, is associated with an increased risk for developing anticitrullinated protein antibody (ACPA)-positive and ACPA-negative rheumatoid arthritis (RA), according to the results of a large case-control study (Zeng P, et al. RMD Open. 2017;3:e000488).
Previous studies have suggested that patients with RA experience worsening of symptoms with exposure to cold air, contact with cold surfaces, and water immersion. Some patients claim that sensitivity to pain and joint stiffness are influenced or even caused by cold exposure.
“Our study, to our knowledge, is the first population-based study that investigates the association between working in cold environment and risk of developing RA among healthy individuals,” wrote Pingling Zeng, PhD, Institute of Environmental Medicine, Karolinska University, Stockholm, Sweden, and colleagues.
Using data from the Swedish population-based Epidemiological Investigation of Rheumatoid Arthritis study from 1996 to 2014, the investigators reviewed questionnaire answers from 3659 patients with RA and 5925 individuals who served as controls.
In the questionnaire, participants were asked about WCE exposure and occupational physical workload. Only exposure up to the year when the first disease symptom appeared (index year) was considered. Controls were assigned the same index year as cases. Exposure to occupational physical workload was assessed based on 7 questions regarding different work postures and movements at baseline and 5 years before baseline. The analyses of associations adjusted for potential confounding factors, including residential area, recruitment time period, age, body mass index, sex, cigarette smoking history, educational level, alcohol intake, silica exposure, occupational class, and occupational physical workloads.
Compared with participants who self-reported no exposure to cold working environments, those who had worked in cold environments had an increased risk for developing RA: odds ratio (OR), 1.5 (95% confidence interval [CI], 1.4-1.7). When the exposure was stratified into cold outdoor and cold indoor environments, exposure to cold outdoor environments increased the odds associated with developing RA (OR, 1.5 [95% CI, 1.3-1.7]) and exposure to cold indoor environments had an OR of 1.7 (95% CI, 1.4-2.1).
For cold outdoor work, similar ORs were observed for current and post exposed groups, whereas for cold indoor work, the ORs of developing RA were 1.5 (95% CI, 1.3-1.7) and 1.7 (95% CI, 1.4-2.1), respectively. These results did not change significantly after adjusting for potential confounders.
Exposure to cold outdoor work and cold indoor work were both associated with an increased risk for developing ACPA-positive and ACPA-negative RA. When the investigators assessed men and women separately, WCE posed an increased risk for ACPA-positive RA (but not ACPA-negative RA) for women, whereas an increased risk for both types of RA was observed in men who worked in a cold environment.
Overall, the risk for developing RA increased with increasing duration, intensity, and cumulative dose of working in cold indoor environments. For example, participants who worked in a cold environment for <5 years had an OR of 1.2 (95% CI, 0.9-1.7) for developing RA versus 2.4 (95% CI, 1.3-4.6) for those who worked in a cold environment for ≥10 years.
A moderate interaction was also observed between repetitive hand/finger movements and cold work environments.
“These findings, if further studied and confirmed, may contribute to the understanding of the disease aetiology, may provide an answer to a question that perplexed patients with rheumatoid arthritis and may have an impact on rheumatoid arthritis prevention,” Dr Zeng and colleagues wrote.
The investigators noted that strengths of their study included the high response rates to the questionnaire (94% among cases and 77% among controls) and the fact the analyses were adjusted for many potential confounding factors. However, they did acknowledge that the definition of a cold work environment in this study was subjected and dependent on self-reports.
“We do not preclude the possibility that maybe subjective feeling of cold at work is a more relevant risk factor for RA as compared with cold temperature,” they wrote.