An invisible threat to newborns’ brains may be hiding in the air we breathe

A new study has found a connection between a pregnant mother’s exposure to air pollution and the brain development of her newborn child. The research suggests that greater exposure to fine particulate matter, known as PM2.5, is associated with lower levels of myelinated white matter, a key indicator of brain maturity, in the first month of life. The findings were published in the journal Environment International.

The research was prompted by the complex and sometimes contradictory nature of air pollution’s components. While pollutants like PM2.5 are broadly associated with negative health effects, they also contain trace elements such as iron, copper, and zinc. These elements are essential for healthy brain development, particularly for myelination, the process of forming a protective sheath around nerve fibers. This dual role complicates the understanding of how air pollution affects the brain during the highly sensitive prenatal period. The study, led by Jesus Pujol of the Hospital del Mar in Barcelona, aimed to disentangle these effects by examining both overall PM2.5 exposure and the specific contributions of these trace elements on the brains of newborns.

The population-based study involved 93 neonates recruited from three major hospitals in Barcelona between 2018 and 2021. To assess prenatal air pollution exposure, the researchers developed sophisticated models. These models estimated daily concentrations of PM2.5 and its metallic components at the mother’s home address. The assessment went a step further by incorporating data on each mother’s daily movements, including time spent at work and during commutes, which was tracked using smartphone applications and questionnaires. This method provided a more personalized and accurate estimate of total exposure during two distinct periods: the embryonic stage (first trimester) and the late fetal stage (third trimester).

Shortly after birth, at an average age of 29 days, the infants underwent magnetic resonance imaging (MRI) scans during natural sleep. The scientists used these brain scans to measure myelination in two different ways. First, an expert manually outlined and calculated the total volume of myelinated white matter across the entire brain, a measure referred to as global myelination. Second, they used an automated technique that analyzes the ratio of different MRI signals to estimate the degree of myelination specifically within the cerebral cortex, the brain’s outer layer.

The analysis revealed distinct associations depending on the timing of the pollution exposure. Higher exposure to PM2.5 during the first trimester, or the embryonic period, was linked to lower levels of cortical myelination in the newborns. In contrast, higher PM2.5 exposure during the third trimester, the late fetal period, was associated with lower global myelinated white matter. These results suggest that air pollution may interfere with the normal timeline of brain maturation. The researchers did not find a similar link between PM2.5 exposure and the overall brain volume, indicating the effect may be specific to the myelination process rather than general brain growth.

When the team examined the trace elements of iron, copper, and zinc, they found a similar pattern. Higher exposure to these metals was also associated with lower myelination. However, when the researchers statistically adjusted for the overall concentration of PM2.5, these specific associations disappeared. This finding suggests that the observed effect is likely driven by the general toxicity of the entire mixture of pollutants in PM2.5, rather than a specific, independent effect of these essential metals.

“Our study shows that the myelination process—a progressive indicator of brain maturation—occurs at a slower rate in newborns most exposed to PM2.5 during pregnancy,” stated Gerard Martínez-Vilavella, a researcher at the MRI Unit of the Radiology Department at Hospital del Mar.

The study authors are careful to point out that a slower rate of early myelination is not necessarily harmful in the long run. Brain development is a highly dynamic process, and its timing can vary. Some previous research has shown that children with higher cognitive abilities sometimes exhibit a slower but more prolonged period of white matter maturation. The current findings raise important questions about how environmental factors influence the tempo of brain development and what the consequences might be.

“In the early stages of life, brain changes are large and complex. Both excessive slowdown and acceleration of brain maturation can be harmful to the child,” added Dr. Jesús Pujol, head of the MRI Unit. “However, it remains to be determined whether the observed effect is necessarily detrimental. This study opens an exciting new field of research aimed at determining the optimal speed of brain maturation during pregnancy and understanding how the mother and placenta may act as effective filters to protect and optimize this process.”

The study has some limitations. The number of infants included was relatively small, which can limit the statistical power to detect more subtle effects. Obtaining high-quality MRI scans from newborns without sedation can be challenging, and estimating pollution exposure, while advanced, is not a direct measurement. The possibility that other unmeasured socioeconomic or environmental factors could have influenced the results also exists.

Despite these limitations, the research provides new insight into the impact of air quality on the earliest stages of human brain development. The authors emphasize the need for longitudinal follow-up studies to track these children as they grow. Such research would help determine if the observed differences in neonatal myelination are temporary or if they are linked to later cognitive or behavioral outcomes.

“Air pollution, specifically PM2.5, is associated with alterations in the myelination process, a fundamental mechanism of brain maturation. Therefore, it is essential to continue controlling pollution levels and to study how this slowdown may affect the later brain development of children,” explained Martínez-Vilavella. He noted that the study also indicates that the effect results from the combination of different components within PM2.5.

The findings also carry significant public health implications, reinforcing the importance of policies aimed at reducing air pollution in urban environments to protect the most vulnerable populations.

Jordi Sunyer, a researcher at the Barcelona Institute for Global Health, emphasized the policy relevance of the work. “The findings in these newborns, born in Barcelona after the first phase of the low-emission zone, warn us that we cannot slacken our efforts to clean up city air. Further steps are needed to meet the new air quality standards.”

The study, “Unraveling the impact of prenatal air pollution for neonatal brain maturation,” authored by Jesus Pujol, Gerard Martínez-Vilavella, Laura Gómez-Herrera, Ioar Rivas, Maria Dolors Gómez-Roig, Elisa Llurba, Laura Blanco-Hinojo, Marta Cirach, Cecilia Persavento, Xavier Querol, Mireia Gascón, Maria Foraster, Juan Domingo Gispert, Carles Falcón, Joan Deus, Payam Dadvand, and Jordi Sunyer.