Air Pollution Exposure in Childhood Linked to Mental Health Concerns at Age 18

New research published in JAMA Network Open highlights the tangible impact of nitrogen oxide and particulate matter, two air pollutants that can impact the central nervous system and lead to both physical and mental health concerns.

These findings underline that children who were exposed to air pollution during development are at increased risk for mental health challenges when compared to their peers who had less exposure.

Understanding the Dangers of Air Pollution

Researchers followed a cohort of 2,039 children born in the United Kingdom during 1994 and 1995 throughout childhood and then interviewed them at age 18 to analyze psychological symptoms as they related to a variety of risk factors.

The research team isolated the risk factor of air pollutants to find that increased exposure to nitrogen oxide and particulate matter correlate with greater risk for mental health concerns.

Helen L. Fisher, PhD, reader in developmental psychopathology at King’s College London, explains that nitrogen oxide (NO_x) should not be confused with nitrous oxide, or laughing gas, which is a different chemical compound.

Nitrogen oxide isn't used at the dentist. Instead, this chemical compound has a strong, harsh odor and comes with a familiar brownish haze that hovers over large cities or industrial zones.

Dr. Fisher says that nitrogen oxide is a regulated compound created by motor vehicles and industrial waste, noting that high concentrations are often found near busy roads. She says that these gaseous pollutants contribute to the formation of smog and acid rain.

Additionally, researchers measured levels of particulate matter or particle pollution, which are extremely small solid particles and liquid droplets also suspended in the air. Dr. Fisher explains, "It mainly comes from motor vehicles, wood burning heaters, and industry. During forest fires or dust storms, particle pollution can reach extremely high concentrations."

Exposure Could Lead to Mental Illness

Researchers found that higher rates of exposure to these air pollutants during childhood and adolescence was associated with greater overall mental health issues by age 18.

Dr. Fisher explains that these mental health issues included internally expressed conditions, such as depression and anxiety; externally expressed conditions, such as conduct disorder and substance abuse; and conditions related to distortions in thinking, such as seeing or hearing things that are not there.

These findings could not be explained by other risk factors, including children's previous mental health concerns, biological factors and family history of mental illness, or risks associated with poverty and neighborhood differences.

Dr. Fisher explains that air pollution is negatively impacting mental health, highlighting that exposure could be considered a risk factor for developing mental illness. Air pollution is already linked to Alzheimer's, Parkinson's, strokes, and other diseases of the central nervous system.

Because of the correlation between early-life exposure and an increased risk of mental health symptoms, additional diagnoses—including mental illness—could be linked with exposure.

How Air Pollution Impacts the Brain

Experts know these toxins impact the brain, made clear by their link to diseases of the central nervous system. But Dr. Fisher explains that further study is needed to understand exactly how air pollution is reaching and harming the central nervous system, highlighting the specific need to continue measuring links between exposure and negative outcomes.

She says that air pollution reaches the brain directly by traveling along the nasal nervous system and can indirectly impact the brain through systemic inflammation. Air pollution is also known to enter the vascular system, which creates a pathway to possibly enter the brain through the blood-brain barrier, a semipermeable border that controls the flow of nutrients and helps to protect the brain from toxins.

Dr. Fisher explains that air pollution can interfere with the brain's ideal function—ultimately leading to the disruption and death of neurons, the cells which receive sensory input and send messages from the brain to other parts of the body. Neurotransmitters, which carry signals between neurons, play a strong role in mental health. Imbalance and disruption are known to lead to certain mental health conditions.

These effects are chronic and cumulative and might not cause tangible effects for many years. Dr. Fisher points out that this is a particular concern for children whose brains may not fully develop or may not function normally if they are impacted, possibly leading to mental health problems.

In addition to affecting mental health by negatively impacting the central nervous system, air pollution is often accompanied by adjacent stressors. Dr. Fisher underlines that nitrogen oxide mainly comes from vehicle emissions and therefore comes with the problem of noisy traffic—which can disrupt sleep and lead to other mental health concerns.

Air Pollution, Global Warming, and Injustice Intersect

Dr. Fisher says more research is needed to understand the impact of air pollution on specific populations. She explains that her findings are most relevant for countries with moderate air pollution and regulatory controls, explaining that research should be continued to determine associations in nations with higher rates of air pollution exposure, including China, Nepal, and India.

The World Health Organization currently estimates that 9 out of 10 people worldwide are exposed to high levels of outdoor air pollutants. Exposure comes from a combination of fossil fuel combustion in vehicles, power plants, and waste disposal as well as manufacturing and industrial processes.

The American Lung Association’s “State of the Air” 2021 report says, “People of color are more than three times more likely to be breathing the most polluted air than white people.” This emphasizes that marginalized people are at much greater risk for exposure and the negative effects that follow.

Elizabeth Brandt, field manager for Moms Clean Air Force, cites “heat islands”—urban areas which experience higher temperatures than surrounding neighborhoods—as a contributing risk factor, because air pollution levels increase when temperatures rise. People who live and work in areas that have a high concentration of buildings with little space for greenery are 1 to 7 degrees hotter than outlying areas. People who are Black, age 65 and older, and/or have lower incomes have historically been most negatively impacted.

Brandt underlines that climate change is impacting air quality for indigenous people as wildfires increase in frequency and intensity on and near Tribal lands. This community is also negatively affected by diesel fuel pollution due to a reliance on older vehicles and, because of a lower rate of access to electricity, more reliance on generators. This highlights the link between systemic oppression and increased risk for exposure to air pollutants.

Overall, air pollution levels dropped during COVID-19 lockdowns, which means exposure likely decreased as well. Projections determined that shifts in behavior due to the pandemic—namely a decrease in travel and daily commutes—reduced nitrogen oxide pollutants in many areas (including major cities) between 11% and 49%. This highlights that as a global community, it's possible to pursue measurable change.

How to Safely Enjoy the Outdoors This Summer

Although concerns about air quality are serious, don't let worries about air pollution keep you inside all season. The Centers for Disease Control and Prevention (CDC) explains that it's still safest to gather with friends and family outdoors, especially if you'll be around those who aren't vaccinated. It's also really good for your mental health.

Teens who were able to get outdoors during lockdown reported higher rates of emotional well-being compared to peers, and that number was even higher when time outdoors was spent with their families. Additionally, experiences in nature reduce symptoms of ADHD and increase both mood and self-esteem.

Brandt underlines that ozone pollution, a broad term that includes nitrogen oxide and other gaseous pollutants, is heat-reactive. This means it's worst when it's hottest outside. For many, air pollution is within acceptable ranges during fall, winter, and spring months but becomes a concern over the summer.

Brandt says that the best way to enjoy the outdoors in warm weather is to plan ahead. Schedule activities for the morning when the sun isn't at its hottest and check the local air quality report before venturing outside.

Understanding the risks will empower everyone to protect themselves and can inspire organized action against pollutants. Seek support through various national and local organizations already gathering resources and making a difference.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.