Central Appalachian coal miners in Kentucky, Virginia and West Virginia are more than eight times more likely than men in the general population to die from respiratory diseases like chronic obstructive pulmonary disease and black lung, according to recent research.

“This higher mortality has also worsened over time with modern miners facing greater risk than their predecessors,” wrote two of the researchers, Kirsten Almberg and Robert Cohen of the University of Illinois Chicago, in a report on the findings published Monday. “Miners in the Central Appalachian states of Kentucky, Virginia, and West Virginia face the most severe risk.”

The study was conducted jointly by researchers at the University of Illinois Chicago and the National Institute for Occupational Safety and Health, an agency within the U.S. Centers for Disease Control and Prevention. It looked at 235,550 deceased miners and is described as “the largest study of its kind to date.”

While rates of black lung, or coal workers’ pneumoconiosis? — an incurable disease caused by the inhalation of coal dust — fell in the U.S. between 1968 and 2006, cases of the most severe form of the disease, known as progressive massive fibrosis, have risen over the past two decades in Central Appalachia.

“This advanced form of (black lung) has recently been found in Central Appalachia at rates not seen since the early 1970s,” wrote the Congressional Research Service in a 2019 report. “In 2017 researchers discovered, among coal miners mostly living in Kentucky and Virginia and served by three federally funded Black Lung Clinics in Virginia, what may be the largest cluster of (progressive massive fibrosis) ever recorded.”

The University of Illinois Chicago-NIOSH study also found coal miners, and particularly those exposed to silica dust, had significantly increased odds of dying of lung cancer compared with the general U.S. population.

Central Appalachian underground mines have been found to have more silica dust on average than mines elsewhere in the U.S.

Current U.S. standards allow coal miners to be exposed to double the level of silica as other workers, although the federal Mine Safety and Health Administration is in the process of tightening those rules.