Pesticides are heavily used in modern life, but what effect do they have on our health? This article sheds light on issues with pesticides as well as solutions.
The human body is a remarkable ecosystem upon which live trillions of microorganisms, with the gut microbiome playing a vital role in our overall health and well-being. However, the pervasive use of pesticides in our environment poses a potential threat to the delicate balance of our gut microbiome.
In this article, we delve into the fascinating world of the gut microbiome and shed light on the often-overlooked risks that pesticides present to its health.
Understanding the gut microbiome
The gut microbiome refers to the diverse community of microorganisms residing in our digestive tract. The study of the gut microbiome has completely revolutionised our understanding of the human body, because these bacteria in our gut can have far-reaching effects. They can of course impact our digestion and our intestine, this is not the surprising part. The more surprising part is that they can produce small molecules, like hormones, which go into our blood, and can influence the function of almost all our organs including the brain (1).
The balance of various microbial species is delicate, and their diversity is crucial for optimal health. A diverse microbial community with a rich array of species is associated with better health outcomes. Reduced microbial diversity, on the other hand, has been linked to an increased risk of various health conditions, including inflammatory bowel disease and metabolic disorders such as obesity and type 2 diabetes (2).
Pesticides: The silent intruders
Pesticides have become ubiquitous in modern society, extensively used in agriculture to protect crops from pests and diseases, as well as in households to eliminate unwanted insects and rodents. These chemicals are designed to be potent and efficient, with the intention of ensuring bountiful harvests. However, the consequences of their widespread use extend beyond their intended targets (3).
These silent intruders find their way into our lives through various pathways. In agriculture, pesticides are applied to crops and can leave residues on the produce that eventually reaches our plates. Additionally, these chemicals can contaminate soil and water sources, further amplifying the risk of exposure. In residential areas, pesticides are commonly used in gardens, parks, and even within our homes, exposing us to their effects through direct contact, inhalation, and ingestion. In a recent scientific study (4), grass samples from playgrounds and school yards in Italy were found to be contaminated by dozens of pesticides. Some of them are known endocrine-disrupting chemicals, a harmful property which raises questions about their potential role in the development of chronic diseases.
Impact of pesticides on the gut microbiome
Scientific studies have begun to unravel the link between pesticides and gut microbiome disruption (5). There is also more information about how pesticides affect our microbiome and allergies in our article “Pollutants, pesticides and our microbiome: How they all affect allergies“. Exposure to pesticides has been shown to negatively affect microbial diversity, composition, and function within the gut. It is still however debated whether pesticide residues present in food and water directly impact the delicate balance of the gut microbiome at environmental levels. Very few pesticides have been studied for their effects on the gut microbiome because testing effects on the microbiome is not required in the battery of tests performed by pesticide companies when they apply for a marketing authorisation. However, there is one case which is well documented: the herbicide glyphosate.
The case of glyphosate
Effects of the major herbicide glyphosate on the gut microbiome are heavily debated. Since glyphosate can kill microorganisms by causing a shortage in aromatic amino acid synthesis, concerns have been raised regarding the potential antibiotic effects of glyphosate. Our team at King’s College London performed a variety of studies to evaluate the effects of glyphosate on the gut microbiome. We tested the effects of glyphosate and a Roundup formulation using the SHIME technology, which mimics the entire gastrointestinal tract (6). Roundup and to a lesser extent glyphosate caused an increase in fermentation activity, resulting in acidification of the microbial environment.
Altogether, glyphosate alone causes limited metabolic alterations even at acute exposure levels, while the combination with surfactants present in a commercial formulation severely affected gut microbial metabolism. We confirmed that commercial formulations have more effects than glyphosate alone in a laboratory model. As part of the multifaceted Global Glyphosate Study, we studied changes in bacterial and fungal populations in the gut of rats exposed prenatally until adulthood to glyphosate or to the herbicide formulations Roundup Bioflow and RangerPro (7). This recent study suggested that glyphosate and its formulations caused profound changes in gut microbiome composition by affecting the gut bacteria, which in turn reduced competition and allowed opportunistic fungi to grow in the gut.
There are however still knowledge gaps to address, including:
- Evaluate if the changes in gut microbiome can have health consequences. It is very difficult to establish causality in science, and it is not fully clear if the effects of pesticides on the human body can be due to an effect on the gut microbiome primarily.
- Evaluate the consequence on intestinal structure. It’s not all about bacteria in the gut ecosystem. The intestines themselves are very important. The nervous system in the gut is so big that it is often called the body’s second brain. Trying to understand the gut ecosystem by only looking at bacteria is like trying to understand how a forest is functioning just by counting the number of animals.
- Evaluate if the effects are due to the surfactants of the formulated products or to their effects on glyphosate absorption. The surfactants in glyphosate formulation are added to increase the stability and penetration of glyphosate in leaves, but they can do the same through our skin.
- Evaluate the effects of glyphosate on the infection by other pathogens. The disturbance of the gut ecosystem by a pesticide could make it more prone to infection. This is what was suggested in our recent study showing that glyphosate disturbed populations of fungi in the gut (7).
The surprising connection to the soil microbiome
Soil microorganisms, including bacteria, fungi, and viruses, play a crucial but often underappreciated role in maintaining human health. They are present in all types of soil and can be found on commonly consumed fruits and vegetables, resulting in widespread human exposure to soil microorganisms.
The gut microbiome is influenced by soil microorganisms (8). Some soil-borne microorganisms, such as Bacillus-related genera, promote the growth of beneficial bacteria in the gut, contributing to gut health. Exposure to certain soil-borne microorganisms, particularly those found in organic-rich soil, can regulate the immune system and reduce the risk of allergies. These microorganisms help train the immune system to recognize and respond to harmless antigens, reducing the likelihood of an overactive immune response and potentially lowering the risk of chronic diseases such as heart disease, diabetes, and certain types of cancer through their anti-inflammatory properties.
While only a few studies have directly linked microbial richness in agricultural products to human health effects, there is an urgent need for comprehensive research in this area. For example, a pioneering study compared the microbiome of apples cultivated with organic and conventional methods, demonstrating the presence and function of microbes linked to significant human health benefits (9).
Effects on the health and resilience of a bee colony
Exposure to pesticides, such as neonicotinoids, glyphosate, organophosphates, and fungicides, can disrupt the diversity and composition of the gut microbiome in honey bees (10,11). These alterations in the microbiota have been associated with negative consequences such as increased susceptibility to pathogens and higher mortality rates. This can have cascading effects on the entire hive.
The overall health and resilience of a bee colony depend on the interaction and interdependence of its members. Disruption of the gut microbiome due to pesticide exposure can lead to impaired digestion, reduced nutrient absorption, and overall compromised health in individual bees. This can affect their ability to perform critical tasks such as foraging, brood care, and thermoregulation.
Navigating pesticide exposure and gut microbiome protection: A need for a precautionary approach
Fortunately, there are steps we can take to minimise pesticide exposure and protect our gut microbiome. Choosing organic produce reduces the intake of pesticide residues in food. Employing natural pest control methods can help reduce pesticide use in our homes and gardens. Furthermore, incorporating fermented foods, prebiotics, and probiotics into our diets can support and restore a healthy gut microbiome.
Another precautionary approach is to have a healthy lifestyle by making sure we activate the self-healing abilities of our body. Our long evolution has equipped our bodies with self-healing mechanisms, and one way to leverage these abilities is fasting. Our bodies have evolved to alternate between periods when they are active, eating, doing some physical activity, and other periods when this activity is interrupted. When we stop eating (so when we start fasting), our bodies activate programs for regeneration and waste clearance. This is true for our body, but also for its inhabitants. Regular fasting has the potential to rebalance the gut microbiome and make it more resilient to challenges such as those posed by our toxic chemical environment (12).
Conclusion
The gut microbiome plays a vital role in our overall health, and the risks posed by pesticides should not be underestimated. By understanding the potential impact of pesticides on gut microbiome health, we can make informed choices and take steps to protect ourselves. It is crucial for herbalists, doctors, and health-conscious individuals to advocate for pesticide regulations, promote sustainable practices, and support further research on this topic. By advocating for pesticide regulations and promoting sustainable farming practices, we can collectively work towards safeguarding our gut microbiome and our health. Let us strive to preserve the delicate balance of our gut microbiome and pave the way for a healthier future.
References
- Chaudhari SN, McCurry MD, Devlin AS. Chains of evidence from correlations to causal molecules in microbiome-linked diseases. Nat Chem Biol. 2021;17(10):1046-56.
- Fan, Y., Pedersen, O. (2021) Gut microbiota in human metabolic health and disease. Nat Rev Microbiol 19, 55–71.
- Mesnage R and Zaller JG, eds. Herbicides: Chemistry, Efficacy, Toxicology, and Environmental Impacts. Elsevier in cooperation with RTI Press. ISBN: 9780128236741
- Linhart C et al. (2021) Year-round pesticide contamination of public sites near intensively managed agricultural areas in South Tyrol. Environ Sci Eur 33, 1.
- Tsiaoussis J., Antoniou MN, Koliarakis I, Mesnage R, Vardavas CI, Izotov BN., Psaroulaki A,, Tsatsakis AM (2019) Effects of single and combined toxic exposures on the gut microbiome: current knowledge and future directions. Toxicology Letters. Volume 312, Pages 72-97.
- Mesnage R, Calatayud M, Duysburgh C, Marzorati M, Antoniou M (2022). Alterations in infant gut microbiome composition and metabolism after exposure to glyphosate and Roundup and/or a spore-based formulation using the SHIME® technology. Gut Microbiome, 1-30.
- Mesnage R, Panzacchi P, Bourne E, Mein CA, Perry M, Hu J, Chen J, Mandrioli D, Belpoggi F, Antoniou MN (2022). Glyphosate and its formulations Roundup Bioflow and RangerPro alter bacterial and fungal community composition in the rat caecum microbiome Front. Microbiol. 13:888853
- Blum WEH, Zechmeister-Boltenstern S, Keiblinger KM. Does Soil Contribute to the Human Gut Microbiome? Microorganisms. 2019 Aug 23;7(9):287.
- Wassermann B, Müller H, Berg G. An Apple a Day: Which Bacteria Do We Eat With Organic and Conventional Apples? Front Microbiol. 2019 Jul 24;10:1629.
- Motta EVS, Raymann K, Moran NA. Glyphosate perturbs the gut microbiota of honey bees. Proc Natl Acad Sci U S A. 2018 Oct 9;115(41):10305-10310.
- Al Naggar Y, Singavarapu B, Paxton RJ, Wubet T. Bees under interactive stressors: the novel insecticides flupyradifurone and sulfoxaflor along with the fungicide azoxystrobin disrupt the gut microbiota of honey bees and increase opportunistic bacterial pathogens. Sci Total Environ. 2022 Nov 25;849:157941.
- Ducarmon Q, Grundler F, Le Maho Y, Wilhelmi de Toledo F, Zeller G, Habold C, Mesnage R(2023) Remodelling of the intestinal ecosystem during caloric restriction and fasting. Trends in Microbiology. DOI 10.1016/j.tim.2023.02.009
