Since 2005, unconventional natural gas development – colloquially, "fracking" – has exploded, particularly in certain states such as Pennsylvania. 

Controversies surrounding fracking rage and range from concerns about the environmental impact of the trade-secret fracking mixture to health concerns. But high-quality data has been relatively scant.

Now a study appearing in JAMA Internal Medicine suggests that unconventional natural gas development may substantially increase the risk of asthma exacerbation among people with asthma.  Here's the breakdown:

Geisinger Health is an integrated healthcare system in Pennsyvlania which captures robust and longitudinal data on its patients visiting a wide variety of affiliated offices, clinics, and hospitals. 

Researchers used this data to identify a population of roughly 35,000 individuals with asthma. Some of those people had exacerbations over the observation period, and some, did not. They identified three classes of exacerbation – mild, moderate, or severe – based on whether it could be treated with a simple medication or whether hospital admission was needed. 

Ok so we have three outcomes so far – mild, moderate and severe asthma exacerbation.

We have 4 exposures. "Fracking" is only one part of well development. The researchers examined the building of the well pad, the drilling-phase, the injection phase, and the pumping phase separately. Lest we focus too much on the mysterious chemical soup that comprised fracking fluid, the researchers point out that well development can lead to many asthma exacerbation risk factors – in addition to chemicals, there is the air pollution from trucks going to and from the site, noise pollution leading to stress and even decreased sleep. The researchers measured the distance between all wells and the patients home address, employing an inverse-square rule for exposure.

Three outcomes, 4 exposures. Twelve total relationships assessed. 

Of the twelve, only one did not show a significant effect on asthma from the wells.  That was the relationship between well-pad-building and moderate asthma exacerbation.  But all 11 other comparisons demonstrated significant associations.

Is this all confounding? People with worse socioeconomic status, and worse access to good primary care may be more likely to live near wells and more likely to have asthma exacerbations. The researchers adjusted for those factors, as best as they could be measured. More compellingly, they utilized a negative control approach. They examined whether well proximity was associated with increased rates of gastrointestinal illness. No such relationship was found.

Before we get our torches and march off to the fracking sites, we should note some limitations here. First, this was a study wherein all people had asthma.  This tells us nothing about whether fracking increases the rates of asthma in a community, only exacerbations.  You could make a somewhat ridiculous argument that for all we know, fracking prevents  asthma – so the people who get asthma near a well have a worse form of it or something like that.

This study would also be strengthened by some direct air-quality measurements. That's a tall-order, but would help to show whether it is the gasses released by natural gas drilling or the ancillary factors that drive these numbers.

In the end, though, this well-done study suggests that the purported public health risks of fracking are not so much hot air.