Air pollution and weight: Can what you breathe impact your gut?

The human gut microbiota has become a popular area of focus in recent years. While more questions than answers surround the microbiota, recent research and knowledge in the area is rapidly growing. 

Our gut harbors a complex community of trillions of microbial cells, which influence a number of functions. Microbial imbalance within the gut has been linked to not only gastrointestinal conditions, but problems outside the gut, such as insomnia, skin conditions and allergies.

After past animal work suggested that exposure to air pollutants may alter the gut microbiota composition, scientists from University of Colorado Boulder wanted to test the theory out in human trials.

Study design

The current research pulled participants recruited from a previous study, the Meta-AIR (Metabolic and Asthma Incidence Research). The study was conducted between 2014 and 2017 at the University of Southern California. 

The Meta-AIR study was part of a larger school-based cohort that began in 2002–2003. The main goal of the Meta-AIR study was to research the impacts of near-roadway exposures on metabolic health and obesity in young adults. 

Participants in the Meta-AIR study were recruited based on their overweight and obese status, which was determined at school visits in 2011–2012. This study also recruited participants to represent the extremes of residential NOx values in Southern California CHS communities using probability weighted sampling from addresses reported at their last school visit. 

Study details 

Using innovative whole-genome sequencing, the research team analyzed fecal samples from 101 young adults in Southern California. 

The researchers analyzed data from air-monitoring stations near the homes of the participants to calculate their previous-year exposure to ozone. This forms when emissions are exposed to sunlight, particulate hazardous matter, and nitrous oxide, the a toxic byproduct of burning fossil fuel. 

Results 

“This study provides the first evidence of significant associations between exposure to air pollutants and the compositional and functional profile of the human gut microbiome. These results identify O3 as an important pollutant that may alter the human gut microbiome,”​ the report noted. 

Specifically, the authors said that using whole-genome sequencing, they found that ozone (O3) exposure is associated with lower gut microbial diversity, higher Bacteroides caecimuris​, and multiple gene pathways. Additionally, air pollution may contribute to alterations in the composition and function of the human gut microbiome.

Of all the pollutants measured, ozone exposure had the greatest impact on the gut microbiota. “The percent variation in gut bacterial composition that was explained by air pollution exposure was up to 11.2% for O3 concentrations, which is large compared to the effect size for many other covariates reported in healthy populations.”​

Ozone exposure had more of an impact on the gut than gender, ethnicity or diet. 

Pollution and weight 

Those with higher exposure to ozone had less bacteria diversity inside their gut. This is a matter of interest considering lower bacteria diversity has been linked with obesity and Type 2 diabetes. 

Additionally, higher ozone exposure was also linked to more Bacteroides caecimuris​, a bacteria species that some studies associated with obesity. 

Overall, the researchers found over 100 bacterial species influenced by increased ozone exposure. 

“We also found that 128 bacterial species were associated with O3 and 4 and 5 bacterial species were associated with NO2 and total NOx, respectively.”​

The bacteria species may impact the release of insulin, metabolite production, among other important functions. 

Influencing policy 

After decades of improvement, air quality in many American cities is worsening, according to the EPA​. 

With air quality playing out against the backdrop, a larger, more expansive study of young adults in the Denver area is in the works. Denver has been identified as one of the areas of noncompliance with the latest air quality rules. Another study which will study early-life exposure to air pollution and its impacts on the development of the gut microbiome is also happening with the help of a grant from the nonprofit Health Effects Institute. 

The authors said they hope their research will weigh on policymakers, who may be swayed to move parks and playgrounds away from busy roads and high pollution areas, as well as invest more in air quality standards.

Source: Environment International ​​​

(2020). DOI: 10.1016/j.envint.2020.105604

“Air pollution exposure is associated with the gut microbiome as revealed by shotgun metagenomic sequencing”​

Authors: F. Fouladi et al.