Air pollution can have a lasting impact on white matter in young brains
Exposure to air pollution during pregnancy and early childhood can lead to lasting changes in the brain’s white matter, which plays an essential role in the nervous system, according to a first-of-its-kind study published in the latest issue of Environmental Research.
The study, led by the nonprofit research center Barcelona Institute for Global Health (ISGlobal), builds on evidence that suggests air pollution affects brain development and causes serious health problems in the heart and lungs. Its results, released Wednesday, highlight “the importance of addressing air pollution as a public health issue, particularly for pregnant women and children.”
“Since these findings were present in children exposed to [particulate matter] concentrations above the currently recommended maximum values by the World Health Organization (WHO), but below those recommended by the European Union (EU), our study provides support for more stringent European guidelines on acceptable levels of air pollution,” the study’s authors conclude.
EU air quality standards are less strict for all pollutants than WHO air quality guideline levels, and air pollution remains a “major health concern” for Europeans, according to the European Environment Agency. The U.S. also falls short. The Environmental Protection Agency (EPA) earlier this year revised its National Ambient Air Quality Standards (NAAQS) for particulates to 9.0 micrograms per cubic meter, which is still nearly double WHO guidelines.
White matter consists of nerve fibers (like communication cables) connecting regions and transmitting signals within the brain and between the brain and spinal cord. These new findings suggest that air pollutants’ detrimental effect on white matter microstructure occurs—and can sometimes persist—as children age.
“Even if the size of the effects were small, this can have a meaningful impact on a population scale,” says Mònica Guxens, an ISGlobal researcher and co-author of the report.
According to ISGlobal, this also marks the first time researchers have studied a large cohort through childhood to investigate the association between air pollution and white matter microstructure. The team followed more than 4,000 participants of the Generation R Study in Rotterdam, the Netherlands, from birth to adolescence.
Researchers estimated the amount of exposure to 14 different air pollutants, such as fine particles (PM2.5) and gases such as nitrogen oxides (NOx), based on where participants lived. (School environments were not included.) Fine particles and nitrogen oxides are typically combustion (burning) byproducts of emissions from automobiles, power plants, and industries or sources such as construction sites and fires.
For 1,314 children, the researchers used data from two brain scans—one performed around age 10 and another around age 14—to examine changes in white matter microstructure. They found:
- Higher exposure to certain air pollutants was linked to persistent lower levels of fractional anisotropy (FA), which measures how water molecules spread within the brain (i.e., the less mature the brain, the more water flows in all directions and the lower the fractional anisotropy level).
- Every increase in air pollution exposure level corresponded to a 5-month delay in the development of FA.
- Certain pollutants also caused changes in mean diffusivity, a measure of the integrity of the brain’s white matter, which declines with age. Some changes diminished as the children got older, while others persisted.
More research is needed to determine precisely how changes occur. “[Lower] fractional anisotropy is likely the result of changes in myelin, the protective sheath that forms around the nerves, rather than in the structure or packaging of the nerve fibers,” says Michelle Kusters, ISGlobal researcher and first author of the study.
It’s not known precisely how air pollution affects myelin. Researchers believe it could be due to small particles entering the brain or inflammation due to particles in the lungs. Damage to myelin can affect nerves’ ability to send and receive electrical signals, as with demyelinating diseases such as multiple sclerosis (MS) and acute disseminated encephalomyelitis (ADEM).
References
Kusters MW, Lopez-Vicente M, Muetzel RL et al. Residential ambient air pollution exposure and the development of white matter microstructure throughout adolescence . Environ Res. 2024. doi: 10.1016/j.envres.2024.119828.2024.
Reuben, A, Arseneault, L, Beddows, A. et al. Association of Air Pollution Exposure in Childhood and Adolescence With Psychopathology at the Transition to Adulthood. JAMA Netw Open. 2021;4(4):e217508. doi:10.1001/jamanetworkopen.2021.7508
Related:
Granés, L., Essers, E., Ballester, J. et al. Early life cold and heat exposure impacts white matter development in children. Nat. Clim. Chang. 14, 760–766 (2024). https://doi.org/10.1038/s41558-024-02027-w
Guxens M, Lubczynska MJ, Perez-Crespo L, et al. Associations of Air Pollution on the Brain in Children: A Brain Imaging Study. Res Rep Health Eff Inst. 2022;2022(209):1-61.
Lynne Peeples. “How air pollution threatens brain health.” PNAS, June 2020: 117 (25) 13856-13860.
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