Air pollution is a known contributor to disease, which is why regulators like the Environmental Protection Agency (EPA) establish limits on emissions. However, growing evidence indicates that pollution levels previously thought to be safe can still increase the risk of health issues, including those related to the brain.
Pollutant levels considered safe cause changes in brain function over time
Research from the Keck School of Medicine of USC, funded by the National Institutes of Health and the EPA, has demonstrated that even levels of certain pollutants considered safe by the EPA are associated with changes in brain function over time. The study, recently published in the journal Environment International, utilized brain scan data from over 9,000 participants in the largest-ever nationwide study of youth brain health, the Adolescent Brain Cognitive Development (ABCD) study. Children exposed to more pollutants showed changes in connectivity between various brain regions. In some areas, they had more connections than normal, while in other areas, they had fewer.
Communication between regions of the brain is crucial to navigating almost every aspect of our daily lives, from how we perceive information about our surroundings to our thoughts and emotions. Many of these vital connections develop between the ages of 9 and 12 and can influence whether children experience typical or atypical cognitive and emotional development.
Megan M. Herting, PhD, associate professor of population and public health sciences at the Keck School of Medicine, said:
“Air quality across America, even though ‘safe’ by EPA standards, is contributing to changes in brain networks during this critical time, which may reflect an early biomarker for increased risk for cognitive and emotional problems later in life.”
Changes in brain connectivity
Researchers Herting, Cotter, and their colleagues analyzed functional MRI scans from 9,497 participants in the ABCD study to investigate the relationship between air pollution and brain development. They collected baseline brain scans from children ages 9 to 10, and a subset of children had follow-up scans two years later to observe how brain connectivity changed over time. The researchers analyzed the salience, frontoparietal, and default-mode brain networks, as well as key regions of the brain known to be involved in emotion, learning, memory, and other complex functions, such as the amygdala and hippocampus.
The researchers used EPA and other data to map air quality at each child’s residence, including levels of fine particulate matter (PM2.5), nitrogen dioxide (NO2), and ground-level ozone (O3). They then used advanced statistical tools to investigate how air pollution levels relate to changes in brain connectivity over time, to determine if young brains develop differently when exposed to more pollution.
The research found that greater exposure to PM2.5 was linked to relative increases in functional connectivity between regions, while more exposure to NO2 predicted relative decreases in connectedness. Exposure to higher levels of O3 was associated with greater connections within the brain’s cortex, but fewer connections between the cortex and other regions such as the amygdala and hippocampus.
To rule out other factors that could explain differences in brain development, the researchers controlled for sex, race/ethnicity, parental education level, household income, urban versus rural location, and seasonality, as air pollution varies across winter and summer months.
Tightening air quality rules
The research suggests that regulators should consider brain health in addition to lung and cardiometabolic health, when setting or adjusting air quality recommendations. The EPA proposed strengthening standards for PM2.5 earlier this year, but guidelines for annual NO2 have not changed since they were first set in 1971.
The study found that despite relatively low air pollution levels in the U.S., the brain is still significantly affected. Policymakers should take this into account when considering whether to tighten current standards.
To determine how and why pollutants harm the brain, Cotter, Herting, and their colleagues plan to examine the chemical composition of pollutants more closely. This could aid in refining regulations. They also plan to continue analyzing brain health over time using data from the ABCD study.
Herting said,
“Long term, does this lead to risk for psychopathology that continues to ramp up during mid- to late- adolescence? How does this affect people’s trajectory of mental health?”
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CT head scan years after brain injury showing empty space where damage occurred via Wikimedia Commons by James Heilman with usage type - Creative Commons LicenseFeatured Image Credit
CT head scan years after brain injury showing empty space where damage occurred via Wikimedia Commons by James Heilman with usage type - Creative Commons License
