Higher neighbourhood air pollution linked to slower brain maturation in early teens

Analysis of more than 3,600 US children found that higher exposure to PM2.5 and ozone was associated with smaller gains in cognitive skills and brain maturation over two years.

Air pollution in the neighbourhoods where children live may be linked to slower brain development during the early teenage years, according to research based on the large Adolescent Brain Cognitive Development study. The analysis found that preteens exposed to higher levels of fine particulate matter, known as PM2.5, or ozone showed smaller gains in thinking skills over two years, along with less change in brain structure and network organisation than similar children in cleaner-air areas. The findings were published in Developmental Cognitive Neuroscience.

The study adds to a growing body of research suggesting that the air children breathe may shape more than lung health. In adolescence, the brain is still undergoing rapid development, with attention, memory, processing speed and cognitive control continuing to improve. At the same time, the cortex normally becomes thinner and brain networks become more specialised. Scientists have long suspected that pollutants such as PM2.5 and ozone could interfere with that process, but earlier findings have been mixed, and it has been difficult to separate pollution effects from the wider social and neighbourhood conditions that often travel with them.

Omid Kardan of the University of Michigan and colleagues analysed data from 3,645 children who had usable brain scans and cognitive testing at the start of the study and again about two years later. The broader ABCD project follows nearly 12,000 children across 21 sites in the United States, with participants originally enrolled at ages 9 to 10.9. To focus on pollution exposure rather than broader demographic differences, the researchers matched children exposed to high pollution with peers from lower-pollution areas on household income, parental education, race and ethnicity, sex and age, while also adjusting for puberty, mental health symptoms and neighbourhood disadvantage.

Using estimated pollution levels around each child’s home, the researchers defined high exposure as annual PM2.5 above 9 micrograms per cubic metre and high ozone above 70 parts per billion, based on Environmental Protection Agency standards. No child in the sample met the threshold for high nitrogen dioxide exposure, so that pollutant was not analysed. The team found that children in the lower-pollution groups showed the expected increase in a combined measure of neurocognitive maturation, while the high-PM2.5 and high-ozone groups did not. That index brought together performance on cognitive tasks, average cortical thickness and a measure of how closely brain network organisation resembled the adult pattern rather than the infant one.

The differences were modest, but they were consistent. Children in less polluted areas showed greater improvement in cognitive performance, more maturation in brain network organisation and more cortical thinning, which is normally part of healthy development at this age. The associations held even after accounting for exposure to the other pollutant. In a conclusion quoted by PsyPost, the study authors said, “As healthy cognitive development is central to multiple domains of resilience and academic achievement, more effort should be directed toward reduction of these pollutants in residential and school areas.”

Still, the researchers cautioned that the findings are observational and cannot prove that pollution caused the differences. The exposure estimates were based on ambient air quality near the home and may not reflect what children actually breathed day to day, especially if they spent time elsewhere or moved during the study. The pollution data also captured conditions only at the start of the project, leaving earlier exposures, including before birth, largely unknown. The ozone measure may also have overstated exposure in some cases because it used the year’s highest level rather than the EPA’s standard calculation. Even so, the study adds weight to concerns that air quality may play a role in children’s neurodevelopment, particularly in communities already facing environmental and social disadvantage.