Microbiota under pressure: how the exposome promotes chronic disease

Psychiatric disorders

A number of studies have shown that exposure of the gut microbiota to environmental factors has consequences for mental health:

• Stress during pregnancy, by disrupting the maternal  microbiota, increases the risk of psychiatric disorders in offspring ²¹;
• Stress associated with a reduction in microbial biodiversity in the environment, by disrupting the gut barrier, is thought to promote systemic inflammation, which is known to play a role in certain psychiatric disorders, particularly depression ;
• The Mediterranean diet (sidenote: Mediterranean diet Rich in fruit, vegetables, cereals, oilseeds (nuts) and fish, and low in red meat, saturated fats and dairy products. Lăcătușu CM, Grigorescu ED, Floria M, et al. The Mediterranean Diet: From an Environment-Driven Food Culture to an Emerging Medical Prescription. Int J Environ Res Public Health. 2019 Mar 15;16(6):942. ) has been shown to improve cognitive function and ward off depression by increasing anti-inflammatory bacterial metabolites and decreasing those that are pro-inflammatory ^23,24.

Moreover, an imbalance in the microbiota can expose the brain to disturbances via the gut-brain axis. A gut dysbiosis may thus be involved in the initial onset of psychosis. 

Asthma and allergic diseases

The number of people affected by allergic diseases continues to rise worldwide. This surge in allergies may well originate in the exposome.

A growing number of studies suggest that exposure to environmental substances (air pollution, detergents, microplastics, nanoparticles, processed foods, emulsifiers, etc.), as well as the decline in biodiversity and environmental degradation, are responsible for changes that favor these immune disorders:

• disruption of epithelial barriers in the skin, respiratory tract, and gut;
• changes in microbial composition of the  microbiota. 

At gut level, certain exposure factors have been shown to damage epithelial barriers, resulting in dysbiosis and increased permeability. This is thought to be responsible for a loss of the “immunomodulatory” (allergy-protective) effects of bacteria in the  microbiota ²⁵ . 

Cancer and bowel diseases

More and more young people are being diagnosed with cancer, including bowel cancer. Over the past three decades, the incidence of cancer has risen by around 50% among people aged 25 to 49 in the US, Canada, Australia, and several European countries. 

The same is true of chronic inflammatory bowel disease (IBD), the highest incidence of which is found in the most industrialized countries, such as those in north-western Europe and the United States, and whose frequency increases with socio-economic development. 

Although the causes of IBD remain poorly understood, dysbiosis is known to play an important role ²⁹.  

According to a team of French researchers, there’s growing evidence that ultra-processed foods (UPFs), in particular food additives, play a role in IBD, colorectal cancer, and irritable bowel syndrome. In particular, emulsifiers, sweeteners, colorants, microplastics, and nanoparticles are known to affect the gut microbiota, intestinal permeability, and intestinal inflammation, with a potentially significant impact on the risk of intestinal disease ³⁰. 

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