Men who worked as coal miners had an increased risk for developing arthritis, particularly rheumatoid arthritis (RA), a telephone survey of residents of Appalachia found.
Among men who had been employed in coal mining for at least 1 year, the estimated odds ratio for any type of arthritis, including degenerative arthritis, was 2.3 (95% CI 1.6-3.2), according to Paul D. Blanc, MD, of the division of occupational and environmental medicine at the University of California, San Francisco, and colleagues.
But for autoimmune RA specifically, the odds ratio was 3.6 (95% CI 2.1-6.2), the researchers reported online in .
"There has been a lot of concern about overexposure to dust in the coal mining industry," Blanc told ľֱ. And these findings have important implications for public health and compensation, he and his colleagues noted. "Given that treatment guidelines for RA indicate that a disease-modifying agent should be initiated soon after onset of disease, earlier disease detection could be achieved through targeted surveillance among current and former coal miners," they wrote.
In addition, it has become clear that occupational exposures occur even above levels that are considered illegal. "We're not even following the standards we have," Blanc said in an interview.
Numerous studies have implicated exposure to mineral dust, especially silica, with RA, and rates of arthritis among men typically are much higher in coal mining areas such as West Virginia, with a prevalence of any type of arthritis of 32.8%, compared with 15.7% in California, which has few coal miners. But little is known about the types of arthritis among coal miners.
To address this question, his group surveyed men older than 50 in select areas of West Virginia, Kentucky, Ohio, Pennsylvania, Virginia, and Tennessee, where there have been high mortality rates from pneumoconiosis among coal miners. The 973 participants answered questions about sociodemographics, employment, smoking (another strong risk factor for RA), and arthritis in general.
And among those reporting coal mining employment, details were ascertained about duration and type of dust (coal, silica, sand, concrete) and type of exposure such as rock drilling or roof bolting, which are considered particularly hazardous for silica dust exposure during coal mining. Participants also were asked about 13 ergonomic factors that could contribute to degenerative arthritis (osteoarthritis) such as bending and lifting.
Among those who reported having been diagnosed with RA, only those who had been given a prescription for glucocorticoids were included to increase the specificity of the diagnosis.
Participants' mean age was 66, and more than 90% were white. Ever smoking was reported by 87%, with a mean pack-year history of 30 years. Any arthritis was reported by 53%, RA by 12%, and other autoimmune diseases such as lupus by 3%.
A total of 27% reported any coal mining employment, with half of those working underground, which increases the exposure to coal dust. Either coal mining or exposure to silica dust was reported by 47%, and mean duration of coal mining employment was 21 years.
Exposure to at least 11 ergonomic factors was associated with a significantly increased likelihood of any arthritis (OR 1.5, 95% CI 1.1-2) but not for RA (OR 1.6, 95% CI 0.97-2.8). In contrast, current smoking doubled the risk of RA (OR 2, 95% CI 1.1-3.9), but did not increase the risk of all types of arthritis.
The researchers also calculated population-attributable fraction -- the proportion of prevalent cases that could be attributed to occupational exposure to either coal or silica dust -- which was 29% (95% CI 21-37) for any arthritis and 44% (95% CI 31-54) for RA specifically. For coal mining work only, the population-attributable fraction was 20% (95% CI 14-25) for any type of arthritis and 33% (95% CI 26-40) for RA, whereas for exposure to silica dust not related to coal mining, the population-attributable fractions were lower, at 10% for both all arthritis and RA. This confirmed that coal mining was the major contributor to risk, the authors noted.
These results "suggest that primary prevention of arthritis [with] workplace protections for dust inhalation may reduce the prevalence of arthritis in general and RA in particular," the team concluded. "We also need to increase the general awareness of the link between exposure and rheumatoid arthritis among generalists and specialists," Blanc said.
Limitations of the study, the researchers said, included the lack of access to medical records and the possibility of misclassification of disease.
Disclosures
The study was supported by the Alpha Foundation and the Russell/Engleman Rheumatology Research Center for Arthritis.
The authors reported no conflicts of interest.
Primary Source
Arthritis Care & Research
Schmajuk G, et al "Prevalence of arthritis and rheumatoid arthritis in coal mining counties of the U.S." Arthritis Care Res 2019; doi:10.1002/acr.23874.