Background/Purpose: Exposure to inhaled mineral dust, particularly silica, has been associated with increased risk of rheumatoid arthritis and other autoimmune diseases. Coal mining, which can involve substantial silica exposure, was strongly linked to risk of RA in our initial survey in the Appalachian region of the U.S.¹ Using additional survey data, we further analyzed the intensity and duration of coal mining-related exposure, in particular from silica, on the risk of RA.

Methods: We conducted a random digit dial telephone survey in 2019 within selected counties in the Appalachian region with the highest coal workers’ pneumoconiosis mortality rates identified by NIOSH, based on our previously validated methods. Eligibility was limited to males age ≥50, with any work history. Structured telephone interviews included demographics, history and details of coal mining work, other occupational dust exposures, and self-reported physician diagnoses of arthritis, including RA. RA was defined 2 ways: based on a reported physician diagnosis and either glucocorticoids or DMARDS prescribed for joint symptoms. We used logistic regression analyses to estimate the risks of any type of arthritis and RA (by each definition), associated with coal mining and other occupational exposures to silica. Additional models estimated risks associated with extensive time worked in underground coal mining and coal mining jobs with high intensity silica exposure, based on data from occupational health analyses.  All models controlled for age and smoking status (current/former/never). The models of RA risk excluded those reporting a diagnosis of arthritis but who did not meet the given study definition of RA.

Results: We interviewed a population sample of 2,008 men, average age 67±10 years, of whom 93% were white and 58% ever smokers. Coal mining work was reported by 409 (20%) and 557 (28%) reported work-related silica exposure outside of coal mining. Among coal miners, 258/409 had specific job tasks with likely high-intensity silica exposure and 263 worked underground. Arthritis was highly prevalent: 1171 (58%) reported a physician diagnosis of any type of arthritis, RA with glucocorticoids in 202 (10%), and RA with DMARDs in 88 (4%).  Coal mining and other occupational silica exposure were associated with an increased odds of arthritis, with increased risk for RA using either definition (Table 1). Coal mining jobs with high intensity silica exposure and individuals with ≥18 years of underground mining manifested a further step-up in risk of RA.

Conclusion: This study provides further confirmatory evidence for coal mining as a significant risk factor for RA, most saliently by showing increasing risk with increasing exposure intensity and duration.

¹ Schmajuk, et al.  Arth Care Res 2019; 71:1201-1215

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/intensity-and-duration-of-silica-exposure-increase-rheumatoid-arthritis-risk-among-coal-miners/