Traffic Pollution: An Emerging Brain Disease Risk Factor?

Authored by Nancy Zoria, Human Biology, Health, and Society '26

Art by Kaylah Nicholson, Human Biology, Health, and Society '25

While sitting in traffic with the windows down during a long commute, it would never cross one’s mind that this air could one day be researched as a major risk factor for developing brain disease. The Environmental Protection Agency estimates that vehicles cause approximately 75% of carbon monoxide pollution in the United States [1]. Additionally, about 11 million Americans reside within 150 meters of major highways and are exposed to extremely elevated levels of traffic-generated air pollution [2]. Around 99% of the global population breathes air that exceeds the WHO air quality limit [3]. Traffic pollution can have many adverse health consequences; recently, there have been many studies that have investigated how traffic pollution can actually be a leading risk factor for brain disease later in life.

According to “Air Pollution and Incidence of Dementia”, a systematic review published in January 2023, higher exposure to fine particulate matter is directly linked to an increased risk of dementia. Fine particulate matter is classified as pollutant particles that are less than 2.5 microns in diameter suspended in air, (PM 2.5). A meta-analysis was conducted where results from 17 studies were reviewed and 5.5 million of the 90 million participants (6.1%) had developed dementia. The researchers found that people who did not have dementia had a lower average daily exposure to fine particulate matter than people with dementia. Additionally, researchers found that the risk of dementia increased by 3% for every one microgram per cubic meter increase of fine particle matter exposure [4].

A literature review published in 2019, “Neurobehavioral Consequences of Traffic Related Air Pollution,” focused on the correlation between traffic-related air pollution and adverse effects in the central nervous system (CNS) such as increased oxidative stress which can lead to neuroinflammation and degeneration . Vehicle exhaust emission (VEE) is considered to be one of the critical sources of oxidative stress. The three primary gaseous constituents of VEE —CO2, CO, NO2 —are pro-oxidant in nature. Pro-oxidants are responsible for generating reactive oxygen species (ROS) and reactive nitrogen species (RNS) through oxidation. These reactive species activate major glial inflammatory units- astrocytes and microglia. These inflammatory units can induce neurotoxicity and neuronal apoptosis. Hence, even short-term exposure to VEE can lead to an increased level of oxidative stress in adults and therefore neurodegenerative risks. Individuals living and working in areas near heavy vehicle traffic are at the greatest risk for developing neuro-oxidative stress in the future [5].

The most recent study conducted by the University of British Columbia and published in January 2023 found that even brief exposure of just two hours to diesel exhaust can decrease the brain’s functional connectivity. To conduct the study, researchers exposed 25 healthy adults to diesel exhaust and filtered air at different times in a laboratory setting. The brain activity of the adults was measured before and after each exposure using functional magnetic resonance imaging (fMRI). The data revealed changes in the brain’s default mode network (DMN), which is a set of interconnected brain regions that is essential for memory and internal thought [6]. These physiological changes also put the adults at a greater risk for neurodegenerative disease risk.

Traffic air pollution is recognized as the largest environmental threat to human health. People can combat this threat of traffic air pollution and aid in decreasing the amount of vehicle exhaust produced in the environment by taking initiative in promoting carpooling and ride sharing. After learning about the risk of brain disease development that exposure to air pollution can cause, people should be more conscious regarding the usually mindless but harmful act of commuting.

Works Cited

1. Brinson, L. C., & Guzman, F. (2012, August 29). How much air pollution comes from cars? HowStuffWorks. Retrieved March 3, 2023, from https://auto.howstuffworks.com/air-pollution-from-cars.htm

2. A population-based cohort study of traffic congestion and infant growth ... (n.d.). Retrieved March 4, 2023, from https://www.science.org/doi/10.1126/sciadv.abp8281

3. World Health Organization. (n.d.). Billions of people still breathe unhealthy air: New who data. World Health Organization. Retrieved March 3, 2023, from https://www.who.int/news/item/04-04-2022-billions-of-people-still-breathe-unhealthy-air-new-who-data

4. Abolhasani, E., Hachinski, V., Ghazaleh, N., Azarpazhooh, M. R., Mokhber, N., & Martin, J. (2023, January 10). Air pollution and incidence of dementia. Neurology. Retrieved March 3, 2023, from https://n.neurology.org/content/100/2/e242

5. Salvi, A., & Salim, S. (2019, November 21). Neurobehavioral consequences of traffic-related Air Pollution. Frontiers in neuroscience. Retrieved March 3, 2023, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6881276/

6. Jan 24, 2023 | F. more information. (2023, March 2). Traffic pollution impairs brain function. UBC News. Retrieved March 3, 2023, from https://news.ubc.ca/2023/01/24/traffic-pollution-impairs-brain-function/