Exposure to specific pollutants, such as fine particles (PM2.5) and nitrogen oxides (NOx), during pregnancy and childhood has been linked to alterations in the microstructure of the brain’s white matter. Some of these changes can last into adolescence.
Research conducted by the Barcelona Institute for Global Health (ISGlobal), supported by the “la Caixa” Foundation, reveals that exposure to pollutants like fine particles (PM2.5) and nitrogen oxides (NOx) during pregnancy and early childhood is tied to significant changes in the brain’s white matter structure. This study, published in Environmental Research, underscores the need to treat air pollution as a critical public health concern, especially for expectant mothers and young children.
There is growing evidence suggesting that air pollution negatively impacts children’s neurodevelopment. Recent research employing imaging technology has investigated how pollutants affect the white matter of the brain, which is essential for interconnecting brain regions. However, these investigations had limitations as they examined only a single time point and did not track participants throughout childhood.
ISGlobal researcher Mònica Guxens points out, “Tracking participants through childhood and performing two neuroimaging tests for each child would provide deeper insights into whether air pollution’s effects on white matter continue, lessen, or worsen over time.” This was the approach her team adopted.
The study encompassed more than 4,000 participants who were monitored from birth as part of the Generation R Study in Rotterdam, Netherlands. The researchers calculated exposure levels to 14 different air pollutants during both pregnancy and childhood, based on the families’ residential areas. For 1,314 children, data from two brain scans were utilized—one taken around age 10 and the other around age 14—to assess changes in white matter microstructure.
Some impacts linger, while others fade over time
The analysis revealed that exposure to certain pollutants, such as fine particles (PM2.5) and nitrogen oxides (NOx), was associated with variations in white matter development. Notably, higher levels of PM2.5 exposure during pregnancy and increased exposure to PM2.5, PM10, PM2.5-10, and NOx during childhood correlated with reduced levels of fractional anisotropy—a measurement indicating how water molecules diffuse in the brain. In more developed brains, water tends to flow more directionally rather than evenly, resulting in higher fractional anisotropy values. These associations remained consistent during adolescence, suggesting enduring impacts of air pollution on brain growth. Each rise in pollution exposure was linked to a delay exceeding five months in fractional anisotropy development.
Michelle Kusters, another ISGlobal researcher and the study’s lead author, explains, “We believe that the reduced fractional anisotropy likely stems from changes in myelin, the protective layer surrounding nerves, rather than from the structure or arrangement of the nerve fibers.” Although the precise manner in which air pollutants influence myelin is not completely clear, it could involve the penetration of tiny particles into the brain or inflammatory responses triggered by particles entering the lungs. These factors may result in neuroinflammation, oxidative stress, and ultimately, neuronal death, as shown in animal research.
The study also indicated that certain pollutants were related to changes in another white matter measure known as mean diffusivity, which reflects white matter integrity and typically decreases as the brain matures. Increased exposure to pollutants like silicon found in fine particles (PM2.5) during pregnancy was linked to temporarily higher mean diffusivity, which then declined more sharply as the children aged. This suggests that some air pollution effects may lessen over time.
Implications for policy
In summary, the study suggests that exposure to air pollution during pregnancy and early childhood may lead to lasting effects on the white matter of the brain. Guxens notes, “Even if the magnitude of these effects appears small, they can have significant implications on a population level.”
Critically, these findings were evident in children exposed to PM2.5 and PM10 levels that exceeded the recommended limits set by the WHO but fell below those proposed by the European Union. Guxens adds, “Our research reinforces the necessity for more rigorous European air pollution guidelines, which are anticipated to be ratified by the European Parliament soon.”
In earlier research, Guxens and her team demonstrated that early exposure to temperature extremes can also impact white matter microstructure, particularly for children from disadvantaged neighborhoods.
