Rheumatoid Arthritis Risk Rises With Working in the Cold

Working in cold environments is associated with an increased risk of rheumatoid arthritis, a new study from Sweden suggests.

Both genetic and environmental risk factors play a role in disease development, but exposure to cold environments has long been suspected as a factor linked to the development of rheumatoid arthritis.

Led by Pingling Zeng of the Institute of Environmental Medicine in Stockholm, researchers conducted the first population-based study to identify a positive association between working in cold environments and the risk of rheumatoid arthritis among healthy persons. Their findings were published in Rheumatic & Musculoskeletal Diseases.

The study

The study used self-reported information on work environment conditions to investigate whether there is an association between working in cold indoor or cold outdoor environments and the risk of rheumatoid arthritis (overall), anticitrullinated protein antibody (ACPA)–positive rheumatoid arthritis, and ACPA-negative rheumatoid arthritis.

In total, data were analyzed from 3659 rheumatoid arthritis cases, all of which met the American College of Rheumatology (ACR) 1987 or ACR 2010 criteria, and 5925 controls.

In addition, because working in cold environments is often accompanied with exposure to occupational physical workload, researchers also investigated the additive interaction between these occupational exposures as they relate to the risk of rheumatoid arthritis.

Based on answers to a questionnaire, participants were categorized according to whether they had been exposed to cold indoor work environments or to cold outdoor work environments current or past. The researchers then compared the occurrence of rheumatoid arthritis in the exposed and unexposed subjects. Exposure to occupational physical workloads (eg, bending/turning, repetitive hand/finger movements, lifting or carrying more than 10 kg) also was assessed.

The findings

The odds ratio of developing rheumatoid arthritis was 1.5 among subjects who had ever worked in cold work environments compared with those who reported never having been exposed to cold work environments. When the exposure was stratified into cold outdoor and cold indoor environment, the ORs of developing rheumatoid arthritis were 1.5 and 1.7, respectively. These results did not change substantially after adjusting for confounders, such as cigarette smoking, alcohol consumption, education level, body mass index, silica exposure, occupational class, and occupational physical workloads.

“Both exposure to cold indoor work and cold outdoor work were associated with an increased risk of developing ACPA-positive and ACPA-negative RA,” the researchers concluded. A significant additive interaction was also observed between working in cold environments and exposure to repetitive hand/finger movements.

In addition, the risk of rheumatoid arthritis (overall) increased with increasing duration (number of years), intensity (hours/week), and cumulative dose (work-years) of working in a cold indoor environment, though this was not significant for cold outdoor work exposure. A possible reason for this discrepancy might be that outdoor temperature naturally varies seasonally and according to weather, whereas indoor cold temperatures are more stable and consistent. Persons working in cold outdoor environments may also wear more protective clothing. Also, the effect of cold indoor work and cold outdoor work on human physiological response may be inherently different.

Implications

Because this is a population-based study with a high response rate, the magnitude of potential selection bias is decreased, but not eliminated. One potential selection bias might be if non-participating controls are those who tend to work in cold environments-previous analysis concluded that non-participation was associated with low socioeconomic status.

In addition, the exposure in this study is self-reported and subjective, so researchers were unable to give a range of specific temperatures that define cold work environments. Also, because exposure to cold environments has long been speculated as a risk factor for rheumatoid arthritis, recall bias may prevail if participants with a diagnosis of rheumatoid arthritis believe their cold work environment caused their disease and thus recall their exposure differently from controls. This study was also unable to distinguish the effect of cold temperature independently from humidity and barometric pressure.

Further studies are needed to identify the exact elements in the cold work environment that are associated with the increased risk of rheumatoid arthritis, the researchers noted. Still, these findings may contribute to the understanding of disease development and may have an impact on prevention.

References:

Zeng P, Bengtsson C, Klareskog L, Alfredsson L. “Working in cold environment and risk of developing rheumatoid arthritis: results from the Swedish EIRA case-control study.” RMD Open. 2017 Aug 16;3(2):e000488. doi: 10.1136/rmdopen-2017-000488. eCollection 2017.