Workers in the hard rock and other mining industries were significantly more likely to develop rheumatoid arthritis than were controls in the general population, based on data from nearly 2,000 individuals.
Although respirable silica exposure has been consistently linked to rheumatoid arthritis (RA) in a variety of occupations including foundry work, construction, and stone crushing and drilling, the association between RA risk and hard rock mining has not been investigated, lead author Paul D. Blanc, MD, of the University of California, San Francisco, and colleagues wrote in a study published in JAMA Network Open.
“Many clinical rheumatologists and most generalists are unaware that what a person does for a living can be a risk factor for rheumatoid arthritis,” Dr. Blanc said in an interview. “This study makes an important contribution to showing that work exposures can more than double the risk of RA,” he said.
“We were surprised by the widespread nature of the work-related risk within and beyond the mining sector,” Dr. Blanc noted. Given the range of potential occupational exposures, his take-home message to rheumatologists is to ask each and every patient about their work history.
The researchers conducted random telephone surveys of 1,988 men aged 50 years and older living in the Four Corners region of the United States (Colorado, New Mexico, and Utah) in counties selected for high levels of pneumoconiosis mortality. The surveys were conducted between Jan. 12, 2021, and May 4, 2021. The mean age of the study population was 68.6 years, and 82.6% were non-Hispanic White. Approximately half reported being former or current smokers.
RA was defined as having a clinician diagnosis, and was further defined by treatment with corticosteroids or disease-modifying antirheumatic drugs (DMARDs).
A total of 262 respondents (13.1%) reported work in surface mining or ore processing, with no underground exposure; 118 respondents (5.9%) reported work in underground hard rock mining; and 62 (3.1%) reported work in underground mining of other type, primarily coal mining.
Overall, after adjusting for age, smoking, and nonmining silica exposure, any mining work was associated with a three- to fourfold increased risk of RA for individuals with a RA diagnosis who were treated with corticosteroids and those treated with DMARDs (odds ratios, 4.12 and 3.30, respectively).
The risk was approximately nine times and six times higher for individuals with a history of underground soft rock mining (mainly coal, no hard rock mining), with odds ratios of 9.74 and 6.42, for those with RA treated with corticosteroids and DMARDs, respectively.
The odds of RA were higher with coal and other underground fossil hydrocarbon mining, compared with underground hard rock mining, the researchers wrote in their discussion. Reasons for this difference could include the longer employment duration for underground coal mining, but also the possibility that “in coal mining, silica inhalation may not be the sole cause, but rather that carbonaceous materials may also be involved etiologically in RA risk in that occupation,” they wrote. No association was found between increased risk of RA and current or former smoking, they noted, in contrast to the researchers’ previous studies of Appalachian coal miners.
The study findings were limited by several factors including the potential for recall bias and misclassified exposure and diagnoses, the researchers noted. Other limitations include the focus on individuals aged 50 years and older in a limited geographic region of the United States and the relatively short time of employment in mining, they said.
However, the results support previous studies showing an increased RA risk with respirable silica exposure, and suggest that clinicians consider mining among other work exposures that could increase the risk for developing RA, the researchers concluded.
Looking ahead, Dr. Blanc said that additional research is needed to tease out disease progression and severity in the face of past occupational exposures.
The study was supported by the Alpha Foundation and the Russell/Engleman Rheumatology Research Center through grants to the researchers. The researchers had no other financial conflicts to disclose.