Breathing dirty air takes a heavy toll on gut bacteria, boosting risk of obesity, diabetes, gastrointestinal disorders and other chronic illnesses, a new study revealed. The study, published 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 research 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 study senior author Tanya Alderete, Assistant Professor at University of Colorado Boulder in the US. “The takeaway from this paper is that some of those effects might be due to changes in the gut,” Alderete added. 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, Alderete’s previous 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.