Air Pollution Alters Gut Microbiome, Increasing Risks for Diabetes, Obesity, Study Says

Exposure to air pollutants alters the composition of gut microbiota, which increases the risk of obesity, diabetes, gastrointestinal disorders, and other chronic illnesses, according to a study published in Environment International.

This study, which used whole-genome sequencing to determine if air pollutants affect the gut microbiome of 101 young adults in Southern California, was the first of its kind to establish the relationship in humans.

Although several pollutants were identified in sequencing, researchers found that adults exposed to higher levels of ozone (O₃) exhibited less microbial diversity and more of certain species associated with obesity and disease.

“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,” according to a statement.

To determine the association, researchers collected data on the average prior year exposure to ambient and near-roadway air pollutants based on residential addresses. Participants in the study were largely male and of Hispanic origin.

Of all the pollutants found to be associated with microbiome composition, including nitrous oxides (NOx) and fine particulate matter, O₃ exposure had the most significant associations at the phylum and species level of gut bacteria. Four bacterial species were associated with NO₂ and 5 species were associated with total NOx.

Researchers also noted the findings were “robust to adjusting for confounders such as age, sex, Hispanic ethnicity, BMI, season of study visit, parental education (proxy for socioeconomic status), energy intake, and macronutrients (ie, protein, fat, carbohydrates, fiber.)”

Percent variation of gut microbiota composition explained by exposure to air pollutants was 4% for total NOx, 4.4% for NO₂, and 11.2% for O₃ concentrations. In addition, the study found “gene pathways involved in fatty acid synthesis /degradation, were enriched with higher O₃ exposure.” These pathways may play a role in obesity and type 2 diabetes.

“We know from previous research that air pollutants can have a whole host of adverse health effects,” said Tanya Alderete, PhD, an author of the study. “The takeaway from this paper is that some of those effects might be due to changes in the gut…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.”

Air pollution remains a public health challenge faced by many states throughout the country. According to authors, O₃ pollution has worsened throughout much of the United States, despite efforts to improve air quality.

“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,” according to a statement. “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, air pollution is the fifth leading risk factor for mortality and kills around 8.8 million people annually. Authors stress that “most of the disease burden that is attributable to air pollution results from chronic noncommunicable diseases, including respiratory disease and type 2 diabetes.”

Specifically, since 2016 air quality in the United States has declined. “Particulate pollution in the United States increased by 5.5 percent between 2016 and 2018, after declining by over 24 percent between 2009 and 2016,” USA Today reported. The decline varies by region and “in the West and Midwest, the level of particulate pollution worsened by around 10 percent since 2016, while they remained steady in the South and Northeast.”

From a public health perspective, air quality continues to be a major social determinant of health. In a study published in the January issue of The American Journal of Managed Care^® (AJMC^®) researchers used applied machine learned to predict healthcare utilization based on socioeconomic determinants of care.

Researchers found the social determinant of health “most associated with risk was air quality, which had a relative value more twice that of the next determinant, income. Air quality had a relative value more than 30-fold higher than the lowest-weighted determinant, percentage in group living quarters.” Air quality included factors that considered fine particles and ozone in this study.

AJMC^® authors also note “A RAND study of California in 2012 found that, from 2005 to 2007, failure to meet federal clean air standards resulted in 29,808 hospitalizations and ED visits, with more than $190 million in costs from inpatient visits.”

Not only does poor air quality lead to lower health outcomes, higher risks of obesity and diabetes, and increased hospitalizations, it also compounds healthcare costs incurred by patients and providers.

Reference

Fouladi F, Bailey MJ, Patterson WB, et al. Air pollution exposure is associated with the gut microbiome as revealed by shotgun metagenomic sequencing [published online March 2, 2020]. Environ Int. doi: 10.1016/j.envint.2020.105604.