Oil companies that are running controversial “fracking” operations may be doing quite a bit more damage to people’s health than expected: a new study indicates that incidences of heart disease, cancer, neurological problems, and other conditions were more common in residents who lived near such fracking operations.

Fracking, a shorthand term for hydraulic fracturing where oil companies blast a mixture of water, chemicals, and sand to break up stone and free up oil trapped underneath, has been a controversial subject with people complaining that it causes water pollution and could sicken people, and a new study has found that there is some correlation evidence to that argument, according to a Columbus Dispatch report.

The study was published in the journal PLOS ONE by University of Pennsylvania and Columbia University researchers, who looked at fracking in various areas in Pennsylvania in 2007 through 2011 and compared them with hospitalization rates. What they found was alarming: those who lived near fracking operations were far more likely to be hospitalized for a range of conditions.

Water pollution is of course the main health concern about fracking, with expectations that residents are exposed to toxins. But fracking also creates a lot of noise and results in social stressors, the researchers believe, and all these factors could result in the higher rates of hospitalization for cancer and heart disease.

For the study, researchers identified 18 ZIP codes where well densities were greater than 0.79 wells per square kilometer. The hospitalization increase for those zip codes was tremendous: a 27 percent increase. Of course, more research will be needed as correlation does not prove causation, but the findings give scientists a new lead.