Have you ever wondered why so many people nowadays seem to suffer chronic illnesses and conditions? Have you ever heard a grandparent say “Back in my day, nobody had inhalers”? It would seem as though despite the medical advances we’ve made, we are only getting sicker. As you probably know, humans are full of bacteria and living organisms. Microbes are becoming a hot topic with lots of talk about how these organisms affect our overall health. The communities of bacteria that inhabit our bodies are known as the human microbiome. Now, you might be pondering about the connection between bacteria and chronic illnesses. Fear not, for in this post we will explore the fascinating world of the human microbiome.
Based on a review of the deleterious effect of air pollution on the human microbial community, approximately 99% of the world inhales polluted air into their lungs (Gupta et al. 2022). It seems only common sense that this could have major impacts on the bacteria that inhabit our lungs. With the amount of industrialization and major environmental changes that have been progressing in recent history, most people agree that we live in a very different world than our grandparents. A recent study regarding the bacterial diversity in the lower respiratory tract of children, led by Christine Niemeier-Walsh ( Niemeier-Walsh et al., 2021) made some unexpected discoveries regarding the correlation between asthma in children and traffic-related air pollution.
Question
Is there a correlation between exposure to traffic-related air pollution and bacterial diversity in those suffering from asthma?
Evidence
In recent years, it has become increasingly apparent that the microbiome plays a significant role in the health and well-being of the human population. We used to think the lungs were a sterile environment, free from bacteria. Newer studies contradict previous beliefs, it is known that the lungs are not free from bacteria and contain important microbial communities. Thanks to the use of modern microbial identification techniques, we were able to discover the diverse range of species that inhabit the respiratory system (Dickson et al.,2016). This proves that the body is full of different microbial environments that are unique to the individual.
As many large populations have become urbanized, the effects on the human microbiome can be observed in our overall health outcomes. Bacteria is often associated with sickness and uncleanliness and has a negative perception. In reality, we need all those little organisms to function. The bacteria-host relationship is symbiotic, we provide an environment for them to thrive and they perform a wide variety of essential functions for us (DeGruttola et al., 2016). There is an undeniable rise in environmental health concerns such as air and water pollution (Zhang et al., 2023). While there are so many advantages to living in an age of advanced medical knowledge, it cannot be argued that overexposure to modern man-made toxins has negatively impacted our health. According to the State of Global Air Report in 2019, air pollution is one of the major contributing factors to mortality worldwide, coming in at fifth (Health Effects Institute, 2019). With this in mind, it is more important now than ever, to take note of the lasting effects this will have on generations to come as we have all been exposed to the dangers of air pollutants.
Exposure to polluted air introduces potentially harmful gasses and particle matter. This includes ozone, nitrogen dioxide, carbon monoxide, sulfur dioxide, polycyclic aromatic hydrocarbons, and pathogens. Particle matter with a diameter of 2.5 micrometers or less is so small that it can enter and cause damage to the lungs, leading to an imbalance of microbial diversity. (Gupta et al. 2022). This imbalance, known as dysbiosis, can have significant health consequences. There is a shocking range of conditions from inflammatory disease bowel disease, to obesity, to allergic disorders that are thought to stem from dysbiosis (DeGruttola et al., 2016). Even before birth, maternal exposure to pollutants can have a negative impact. As these harmful gasses and particles enter through the respiratory system, they are dissolved in the bloodstream and absorbed by the body (Gupta et al. 2022). The environment to which a mother is exposed before and during pregnancy will also determine the health of the baby. As well, children are subject to air pollution as soon as they are born. Studies have shown that the presence of air pollution in childhood and adolescence may be correlated to changes in the lower respiratory microbiota (Gupta et al. 2022).
Resources such as the Asthma and Allergy Foundation of America suggest that existing asthma conditions are aggravated by poor air quality and pollution (AFAA, 2024). However, the relationship between the type of bacteria and diseases of the lower respiratory tract such as asthma is not very well studied. Leading off of the Cincinnati Childhood Allergy and Air Pollution Study in which children were studied from birth until early adolescence, Niemeier-Walsh and their team took samples from the nose and saliva. Their goal was to compare microbial richness in the respiratory tract of children who had high and low exposure to air pollution.
Figure 1: How particulate matter enters the body. (Image from Breathe Clean Air Comox Valley ).
Usually, we would expect to see positive outcomes from increased microbial diversity in the body, but in the lungs, this is not the case. It is the opposite, diseases such as asthma are correlated to greater bacterial diversity. The researchers theorize that air pollutants allow microorganisms to stick to the inner lining of the respiratory system leading to increased microbial growth and damage to the internal environment. While the association of air pollutants and worsened symptoms of asthma is unknown, the particulate matter present in polluted air allows the fixture of bacteria to epithelial cells. Certain species of bacteria are associated with asthmatic airways including Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis.`
Figure 2. from Niemeier-Walsh et al., 2021: Bacterial diversity between high and low traffic-related air pollution exposure groups; Shannon diversity, number of observed amplicon sequence variants (ASVs), and Faith’s phylogenetic diversity.
From the samples the researchers tested, they concluded that exposure to air pollutants in early childhood leads to increased microbial diversity (Fig 2 ). However, they were unable to directly tie this increase in microbial diversity to the development of Asthma. As expected, they did observe a higher bacterial load in the septum and saliva of asthmatic patients vs nonasthmatic patients, but by taking a close look at the DNA of the bacteria they sampled, they found no significant difference between the bacteria load of high vs low traffic-related air-exposed individuals.
My Questions
As a student aspiring to have a healthcare career, I am very invested in public health. While this study provides a lot of insight into the impact our environment has on the rates of chronic disease. Thanks to the work done by Niemeier-Walsh and their team of researchers, we now have a better understanding of conditions concerning the upper respiratory tract. We are led to question how traffic-related air pollution can affect the upper respiratory microbiome. My question is; what do these impacts mean for the health of the human population? How might asthma be positively or negatively impacted by the communities of bacteria in the upper respiratory tract? In the future, this study could be built upon the incorporation of more participants and the exploration of other diseases of the respiratory tract.
Further Reading
For more information on the management and symptoms of asthma, please see the following article from the Journal of Allergy, Asthma & Clinical Immunology: Treatment strategies for asthma: reshaping the concept of asthma management.
Here you will find lots of information about where this disease comes from and how to treat Asthma: Asthma Treatment strategies for asthma: reshaping the concept of asthma management( Papi et al., 2020)
To learn more about how traffic-related air pollution, I would recommend checking out this article from the Canadian Medical Association where they discuss public health concerns in Canada: Traffic-related air pollution and health in Canada – PMC (Brauer et al., 2013).
Literature Cited
Niemeier-Walsh C, Ryan PH, Meller J, Ollberding NJ, Adhikari A, Reponen T (2021) Exposure to traffic-related air pollution and bacterial diversity in the lower respiratory tract of children. PLoS ONE 16(6): e0244341. https://doi.org/10.1371/journal.pone.0244341
Dickson RP, Erb-Downward JR, Martinez FJ, Huffnagle GB. The Microbiome and the Respiratory Tract. Annu Rev Physiol. 2016;78:481-504. Doi: 10.1146/annurev-physiol-021115-105238. Epub 2015 Nov 2. PMID: 26527186; PMCID: PMC4751994
Gupta N, Yadav VK, Gacem A, Al-Dossari M, Yadav KK, Abd El-Gawaad NS, Ben Khedher N, Choudhary N, Kumar P, Cavalu S. Deleterious Effect of Air Pollution on Human Microbial Community and Bacterial Flora: A Short Review. Int J Environ Res Public Health. 2022 Nov 22;19(23):15494. doi: 10.3390/ijerph192315494. PMID: 36497569; PMCID: PMC9738139.
Fouladi F, Bailey M, Patterson W, Sioda M, Blakley I, Fodor A, Jones R, Chen Z, Kim J, Lurmann F, Martino C, Knight R, Gilliland F, Alderete T. Air pollution exposure is associated with the gut microbiome as revealed by shotgun metagenomic sequencing, Environment International, Volume 138, 2020, 105604, ISSN 0160-4120, https://doi.org/10.1016/j.envint.2020.105604
Health Effects Institute. (2019). State of Global Air 2019. Special Report. https://www.healtheffects.org/announcements/state-global-air-2019-air-pollution-significant-risk-factor-worldwide
Asthma and Allergy Foundation of America (AAFA). 2024. Air pollution and asthma. Retrieved from https://aafa.org/asthma/asthma-triggers-causes/air-pollution-smog-asthma/
Papi, A, Blasi, F, Canonica, G.W. et al. Treatment strategies for asthma: reshaping the concept of asthma management. Allergy Asthma Clinical Immunology 16, 75 (2020). https://doi.org/10.1186/s13223-020-00472-8
Brauer M, Reynolds C, Hystad P. Traffic-related air pollution and health in Canada. CMAJ. 2013 Dec 10;185(18):1557-8. doi: 10.1503/cmaj.121568. Epub 2013 Oct 21. PMID: 24144607; PMCID: PMC3855107.
Zhang Z, Zhao M, Zhang Y, Feng Y. How does urbanization affect public health? New evidence from 175 countries worldwide. Front Public Health. 2023 Jan 6;10:1096964. doi: 10.3389/fpubh.2022.1096964. PMID: 36684862; PMCID: PMC9852986.
DeGruttola AK, Low D, Mizoguchi A, Mizoguchi E. Current Understanding of Dysbiosis in Disease in Human and Animal Models. Inflammatory Bowel Disease. 2016 May;22(5):1137-50. doi: 10.1097/MIB.0000000000000750. PMID: 27070911; PMCID: PMC4838534.