It's a given: polluted air is bad. However, it's only recently that we've begun to understand the extent to which air pollution poses a danger to our health. It increases the risk of developing respiratory and cardiovascular diseases, and is thus responsible for millions of deaths. premature deaths around the world.
More recently, experts are beginning to see that the brain is not spared by pollution, which would increase the risk of neurological diseases such as Alzheimer's disease.
And this harmful impact would be visible from childhood. Already in 2017, a study showed that children exposed to polluted air had poorer memory performance. Since then, a large number of studies have elucidated the consequences of air pollution on brain development, showing how harmful it is.
This work was summarized by researchers from the University of California at Davis (USA) in a review published in October 2024 in the journal Developmental Cognitive Neuroscience.
Exposure to air pollution at a young age could cause brain damage
Some forty studies were analyzed, the majority from Europe, the United States, and Mexico. Nearly half of them focused on the effects of air pollution on the structure of children's brains, with alarming results. They highlight that exposure to polluted air causes visible changes in the brain, particularly in the volume of certain regions.
For example, magnetic resonance imaging (MRI) scans show that exposure to polluted air before birth (in utero) or during the first year of life was associated with a decrease in the volume of gray matter in the cerebellum (important for motor skills and cognition) in adolescence.
This is also the case for other areas of the brain, whose size is thought to decrease due to air pollution. The authors of the review caution, however, that more studies are needed to better understand these consequences, as they appear to vary depending on the pollutant in question and the age at exposure.
These alterations begin at the molecular level
Other studies have taken a closer look at the impact of pollution on the brain. Some have observed the functioning of neural networks, using techniques such as diffusion MRI (which allows us to observe brain connectivity) and functional MRI (which allows us to see brain activity).
The first technique highlighted alterations in the microstructure of white matter, the internal part of the brain that connects the different regions of gray matter (the cortex, on the periphery of the brain). While functional MRI showed alterations in the maturation of neural networks and their connectivity.
Other techniques have shown an association between air pollution and alterations in brain metabolism, as well as changes in DNA methylation in genes linked to neuronal development.
That is, exposure to air pollution before birth and during childhood would affect the expression of these genes, and could thus cause alterations in brain development. This could explain the differences observed in brain structure and neuron connectivity.
Air pollution increases the risk of central nervous system cancer
These changes in the brain caused by air pollution could have serious consequences for health, particularly by increasing the risk of developing a tumor.
Eight studies have analyzed this risk, showing that there is a higher incidence of central nervous system tumors in geographic areas most exposed to air pollution. And four autopsy studies revealed that in these areas more exposed to pollution, the bodies studied showed more vascular and structural damage to the brain.
“ Many brain development specialists, whether studying autism, Alzheimer's disease, or other conditions, did not consider environmental factors, believing that genetics or other factors unrelated to air pollution were the sole causes., regrets in a communicates Anthony Wexler, author of the review and director of the Center for Air Quality Research at the University of California, Davis.
He hopes the evidence from all these studies will be game-changing, and that this new insight will help us understand (and perhaps avoid) the harmful impact of air pollution on brain development and brain health throughout life. This is an urgent matter, and it's also becoming a matter of course.
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