Air pollution and the gut microbiome: you are what you breathe
A dark cloud of smog lingering on the horizon is likely more than just an eyesore—research suggests that long-term exposure to high levels of air pollution increase an individual’s risk of developing obesity, type 2 diabetes, and other metabolic dysregulations during their lifetime. The direct pathways and biological mechanisms underpinning these relationships, however, remain unclear. What we do know is that air pollution is associated with increased levels nitrogen dioxide, nitrogen oxides, and ozone (O3) among other factors.
A group of researchers from California recently explored the effect of air pollution on the gut microbiome with the use of shotgun metagenomic sequencing. Researchers examined 101 participants from the Meta-AIR cohort, which consists of young adults living throughout the Southern California area with various levels of air pollution. They performed a variety of clinical assessments, including blood pressure, oral glucose tolerance, and insulin resistance. To examine the gut microbiome, fecal samples were collected with Norgen’s stool preservative, and subsequently analyzed by shallow whole-genome sequencing.
After adjusting for other variables, results demonstrated that exposure to high O3 levels in particular were significantly correlated with gut bacterial species composition. Interestingly, higher exposure to O3 was associated with a lower Shannon diversity index and a significantly higher amount of Bacteriodes caecimuris specifically.
Overall, the three air pollutants examined (NO2, NOx and O3 concentrations) were related to the highest amount of variation in the gut microbiome when compared to other factors such as energy intake and BMI. Researchers also found that O3 exposure in particular altered gene pathways involved in fatty acid synthesis and degradation.
Further research examining a broader range of participants will be necessary to expand on these conclusions in the context of confounding variables, as well as to explore the biological mechanisms behind such results. Nevertheless, this study provides an insightful first look into the effect of air pollution on gut health.
Figure 1: Exposure to Air pollutants was Associated with the Gut Microbiota at the Phylum and Species Level Using Whole Genome Sequencing (WGS). Figure shows the results from a non-parametric multivariate ADONIS test with 10,000 permutations. For each explanatory variable, separate multivariate models were constructed to determine the association between the gut microbiota composition and each explanatory variable at the level of the phylum (A) and species (B). R2 values correspond to the fraction of variation in the gut microbiota composition that is explained by each variable. Red bars indicate statistical significance (FDR corrected p-value < 0.05).
Figure 2: Exposure to O3 was Associated with the Gut Microbiota at the Phylum Level Using Whole Genome Sequencing (WGS). Univariate linear regression was used to determine the association between the relative abundance of gut bacterial phyla and each explanatory variable. The heatmap shows R2 values, which are indicative of the amount of variation explained by each explanatory variable in univariate regression models. ** FDR-corrected p-value < 0.01, * FDR-corrected p-value < 0.05.
Paper: Fouladi, Farnaz, et al. “Air pollution exposure is associated with the gut microbiome as revealed by shotgun metagenomic sequencing.” Environment International 138 (2020): 105604.
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