Breathing dirty air takes a heavy toll on gut bacteria, boosting the risk of obesity, diabetes, gastrointestinal disorders and other chronic illnesses, finds new University of Colorado Boulder research.
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 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.
Previous research has connected air pollutants to type 2 diabetes, weight gain and inflammatory bowel diseases. Those effects may be due to changes in the gut.
Worldwide, air pollution kills 8.8 million people annually, more than smoking or war.
Studies have shown pollution can also impair the body's ability to regulate blood sugar and influence 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 greater risk of developing Crohn's disease.
About the study
To investigate what might be going on inside the gut, the research team analyzed fecal samples from 101 young adults in Southern California.
The researchers looked at data from air-monitoring stations near the participants’ addresses to calculate their previous-year exposure to ozone (which forms when emissions from vehicles are exposed to sunlight), particulate matter (hazardous particles suspended in the air), and nitrous oxide (a toxic by-product of burning fossil fuel).
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 participants, 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 bacterial species called Bacteroides caecimuris. 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 clearing glucose from the bloodstream. 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.
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