A new study links air pollution to changes in the human gut microbiome which could fuel diabetes, obesity and inflammatory bowel diseases like colitis and Crohn’s disease.

The study, published online in the journal Environment International, 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 gaseous pollutant ozone, which helps make up Denver’s infamous ‘brown cloud’ — is particularly hazardous, the study found, with young adults exposed to higher levels of ozone showing less microbial diversity and more of certain species associated with obesity and disease.

«We know from previous research that air pollutants can have a whole host of adverse health effects,» said senior author Tanya Alderete, an assistant professor of integrative physiology, pointing to studies linking smog with Type 2 diabetes, weight gain and inflammatory bowel diseases. «The takeaway from this paper is that some of those effects might be due to changes in the gut.»

The study comes at a time when 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.

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Materials provided by University of Colorado at Boulder. Original written by Lisa Marshall. Note: Content may be edited for style and length.