Background/Purpose:  Exposure to inhaled mineral dust, particularly silica, has been associated with increased risk of RA and other autoimmune diseases. Coal mining leads to silica exposure, but the extent to which RA can be attributed to coal mining has not been estimated. We studied the association of RA with work-related coal and silica exposure in the Appalachian region of the US, given its geographic concentration of mining and data showing a high population prevalence of arthritis.

Methods:  We conducted a random digit dial telephone survey within selected counties in the Appalachian region with the highest coal workers’ pneumoconiosis mortality rates identified by NIOSH. Eligibility was limited to males, age ≥50, with any work history. A brief structured telephone interview included demographics, occupational dust, work-related ergonomic exposures, and self-reported physician diagnoses of and treatment for arthritis, including RA. Only those reporting both a physician diagnosis of RA and glucocorticoid use for joint symptoms were considered to have RA for this analysis. We scored ergonomic exposures using a 13-item list of physical work hazards (e.g. lifting, bending, using power tools), each contributing 1 point. We used logistic regression analysis to estimate the risks of any arthritis and, separately, the subset meeting the study definition of RA associated with occupational coal dust and other occupational silica exposure, adjusting for high-levels of ergonomic exposure (≥11 items; 75^th percentile), age, and smoking status (current/former/never). The models of RA risk exclude those reporting a diagnosis of arthritis who do not meet the study definition of RA.

Results:  Among the 973 men, average age was 66±10 years; 91% were white; 54% ever smokers. 266 (27%) reported coal mining work; 189 (19%) reported work-related silica exposure without coal mining. Arthritis was highly prevalent among the respondents, with 517 (53%) reporting a physician diagnosis of any arthritis and 112 (12%) RA. In the fully adjusted models (Table 1), coal mining was associated with elevated odds of both RA and any arthritis. Other silica exposure also increased the odds of any arthritis. Current smoking was associated with RA only.

Conclusion:   In this population of older men living in areas in which coal mining and other occupational silica dust exposure is common, we found a high prevalence of self-reported arthritis, particularly of RA. While this study may overestimate the true prevalence of RA, the odds of any arthritis and RA associated with coal-mining remained markedly elevated after adjusting for ergonomic exposures and smoking. Given both the frequency of exposure and magnitude of risk, a substantial proportion of prevalent arthritis in this region may be attributable to occupational factors, a link that is not widely appreciated or acknowledged.