About 386 million years ago, Pennsylvania received a great gift—or, depending on your point of view, a curse: the Marcellus Shale, a formation of black rock and limestone containing vast reserves of natural gas. The formation stretches from New York through the Appalachian Basin, but it’s Pennsylvania that has played host to the most intensive plundering of those reserves since the mid-2000s, when energy companies began to use hydraulic fracturing to free up the gas trapped a mile below the surface of the earth.

Pennsylvania will receive another dubious benefaction next week, when Philadelphia hosts the Democratic National Convention. Considering the party’s division over fracking and the shale gas revolution it enabled, it’s a provocative setting. The Obama administration, along with Hillary Clinton as secretary of state and other prominent Democrats, have promoted natural gas as beneficial for both the climate and the economy. But communities situated near heavy fracking activity have long reported adverse environmental and health impacts. And new research on the scale of leaks of methane—a greenhouse gas even more potent than carbon dioxide, in terms of its ability to trap heat in the atmosphere—from natural gas wells and pipelines has intensified calls from climate activists to end the practice. The Democratic platform draft walks a strained line between these two camps, offering support for local moratoriums and more federal oversight, while stopping short of calling for a broader ban.

Now there’s new evidence suggesting the drilling technique may harm human health. On Monday, researchers at the Johns Hopkins Bloomberg School of Public Health released a study of the medical records of more than 35,000 people with asthma who lived above the Marcellus Formation between 2005 and 2012. Residents of areas with intense shale-gas activity faced “significantly higher odds” of having asthma attacks, the researchers found, even when taking into account factors like whether they smoked or lived near major roads. Though the study doesn’t trace an exact line of causality, the authors note that fracking has been linked to increases in air pollution, and stress and sleep deprivation from noisy equipment and bright lights, all of which can worsen asthma.

Larysa Dyrszka, a doctor and co-founder of Concerned Health Professionals of New York, said during a press call Tuesday that there have been more than 480 studies linking adverse health outcomes to fracking, including higher rates of hospitalization near fracking hotspots. “I’ve grown increasingly concerned about the health effects of drilling and fracking, as more and more residents report the same symptoms, which include troubled breathing, nose bleeds, rashes and more,” she said. With the newest health study as ammunition, Dyrszka’s group will join a coalition of environmental organizations, labor unions, peace activists, and others in Philadelphia on Sunday for a “March for a Clean Energy Revolution,” calling for a fracking ban, among other things.