In a new study, researchers found that breathing dirty air takes a heavy toll on gut bacteria, boosting the risk of obesity, diabetes, gastrointestinal disorders, and other chronic illnesses.
The gaseous pollutant ozone, which helps makeup Denver’s infamous ‘brown cloud’ – is particularly hazardous, with young adults exposed to higher levels of ozone showing less microbial diversity and more of certain species associated with obesity and disease.
The study is the first to link air pollution to changes in the structure and function of the human gut microbiome—the collection of trillions of microorganisms residing within us.
The research was conducted by a team at the University of Colorado Boulder.
Previous research has shown that air pollutants can have a whole host of adverse health effects.
These studies link smog with type 2 diabetes, weight gain and inflammatory bowel diseases.
The takeaway from this study is that some of those effects might be due to changes in the gut.
The study comes at a time when the air quality in many U.S. cities is worsening after decades of improvement.
In December, the Environmental Protection Agency downgraded the Denver metro and North Front Range regions to “serious non-attainment” status for failing to meet national ozone standards.
Regions of eight other states, including some in California, Texas, Illinois, Connecticut, Indiana, New Jersey, New York, and Wisconsin, were also penalized for high ozone.
Worldwide, according to research published this month, air pollution kills 8.8 million people annually—more than smoking or war.
While much attention has been paid to respiratory health, the team’s previous studies have shown pollution can also impair the body’s ability to regulate blood sugar and influence the risk for obesity.
Other research has shown visits to emergency rooms for gastrointestinal problems spike on high pollution days, and youth with high exposure to traffic exhaust have a greater risk of developing Crohn’s disease.
To examine just what might be going on inside the gut, the team used cutting-edge whole-genome sequencing to analyze fecal samples from 101 young adults in Southern California.
Of all the pollutants measured, ozone had the greatest impact on the gut by far, accounting for about 11% of the variation seen between study people—more of an impact than gender, ethnicity or even diet.
Those with higher exposure to ozone also had less variety of bacteria living in their gut.
This is important since lower (bacteria) diversity has been linked with obesity and Type 2 diabetes.
People with higher exposure to ozone also had a greater abundance of a specific species called Bacteroides caecimuris. That’s important because some studies have associated high levels of Bacteroides with obesity.
In all, the researchers identified 128 bacterial species influenced by increased ozone exposure.
Some may impact the release of insulin, the hormone responsible for ushering sugar into the muscles for energy.
Other species can produce metabolites, including fatty acids, which help maintain gut barrier integrity and ward off inflammation.
The study was relatively small and has some limitations, including the fact that stool samples were taken only once.
The team says a lot of work still needs to be done, but this adds to a growing body of literature showing that human exposure to air pollution can have lasting, harmful effects on human health.
One author of the study is Tanya Alderete, an assistant professor of integrative physiology.
The study is published in the journal Environment International.
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