An increase in natural gas drilling through the method known as fracking led to an increase in hospitalizations, according to a new study published this week in the medical journal PLOS ONE.  

Researchers from the University Pennsylvania and Columbia University looked at hospitalization rates between 2007 and 2011 in Bradford and Susquehanna counties in northeastern Pennsylvania that have seen a rise in fracking wells. A third county, Wayne,where there is a de facto drilling moratorium was used as a control actually saw the number of hospitalizations decline.

The study's authors say their report may be one of the most comprehensive studies to date on the health effects of living near fracking wells.

What the researchers found was that living in zip codes with a high number of wells led to an increase in people seeking medical treatment for heart problems. Zip codes in which fracking wells are particularly dense saw in increase in hospitalizations for neurological problems. 

Other types of conditions, such as skin problems, cancer and urological conditions were also associated with fracking wells, but the impact was less clear. 

But the researchers at the University of Pennsylvania and Columbia University caution that there are limitations to their analysis.

The study does not measure exposure to pollution, so they do not know the precise cause of the medical conditions.

Furthermore, the researchers do not count people who were hospitalized but did not live in one of the counties -- this could point to an undercount of medical conditions associated with workers on drilling rigs who traveled from other states to work in Pennsylvania's oil fields. 

The authors predict that an increase of 25 wells in a zip code could lead to a 2 percent increase in trips to the hospital.