Outdoor air pollution from power plants, fires and cars continues to affect human, animal and environmental health around the world. New research shows that even pollution levels below government air quality standards are linked to differences in children’s brains.
A research team from the University of California, Davis, systematically analyzed forty empirical studies, most of which found that outdoor air pollution is linked to differences in children’s brains. These differences include the amounts of white matter, which are associated with cognitive functions, connections in the brain and even early markers for Alzheimer’s disease.
The study ‘Clearing the Air: A systematic review of studies on air pollution and child brain outcomes to mobilize policy change’ was published this month in Developmental cognitive neuroscience.
We see differences in brain outcomes between children with higher levels of pollution exposure versus lower levels of pollution exposure.”
Camelia Hostinar, associate professor of psychology and corresponding author of the study
Children and teenagers are particularly vulnerable to air pollution because their brains and bodies are still developing. They typically spend more time outdoors and their bodies absorb more pollutants relative to their body weight than adults, researchers said.
Outdoor air pollution and brain development
This study examined 40 published, peer-reviewed studies, all of which included measures of outdoor air pollution and brain outcomes for children of different ages, from newborns to 18-year-old adults. The majority of studies came from the United States, Mexico and Europe, with one each from Asia and Australia.
The studies varied in how they measured brain differences. Some used advanced scanning methods such as magnetic resonance imaging or MRI. Others tested changes in chemical compounds that help with brain function and health. Some studies looked for tumors in the brain or central nervous system.
Studies from Mexico City comparing children from areas with high and low pollution found significant differences in brain structure.
Each study included measurements of air pollution linked to the child’s address or neighborhood, which showed that the children’s brain differences were observed in places with high levels of air pollution and in places that met local air pollution standards.
“Many of these studies include children in places with levels of air pollutants well below the limits set by U.S. or European regulations,” says Anna Parenteau, a Ph.D. student in psychology at UC Davis and co-first author of the study.
Outdoor air pollution
Sources of outdoor air pollution include coal-fired power plants, forest fires, and many other sources near where people live. This systematic review is unique because most others have focused on how air pollution affects adults or animals, researchers said.
“We can’t necessarily apply the findings from adults and assume it will be the same for children,” said Johnna Swartz, associate professor of human ecology and co-author of the study. “We also need to look more at different developmental windows, because that could be very important in terms of how air pollution might influence these brain outcomes.”
To establish a causal link between outdoor air pollution and differences in the brain, the research team looked to experimental research on animals. That study found that pollution leads to many of the same outcomes identified in the studies in this review, including markers for Alzheimer’s disease.
“Many researchers working on brain development, whether in autism, Alzheimer’s disease or something else, have long ignored environmental factors,” said Anthony Wexler, professor at UC Davis and director of the Air Quality Research Center. “They argued that it’s a genetic factor or some factor other than exposure to air pollution. That’s changed a lot lately because of all this research literature.”
Limit damage
This systematic review suggested steps for both parents and policy makers to protect their children from outdoor air pollution, for example by adding air filters to homes and schools near highways.
“We mentioned air purifiers as one of the policy recommendations, and that is something that could be subsidized or offered in schools and other places where children spend a lot of time,” Hostinar said. “These can be quite effective.”
Researchers may also include measurements of air pollution in studies related to brain health or other health outcomes.
“Anyone collecting data from human participants on brain outcomes, cardiovascular outcomes, or anything else can easily add questions to assess air pollution exposure, such as obtaining their addresses,” says Sally Hang, a Ph.D. student in psychology and the first co-author of the study.
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Magazine reference:
Parenteau, A.M. et al. (2024) Clearing the air: a systematic review of studies on air pollution and brain outcomes in children to mobilize policy change. Developmental cognitive neuroscience. doi.org/10.1016/j.dcn.2024.101436.