Long-term exposure to a cocktail of common air pollutants, even at low levels, is associated with increased risk for depression and anxiety, according to a new study published this week.
The study, which followed more than 389,000 adults in the UK for more than a decade, adds to growing research examining the relationship between air quality and mental health, and supports calls from health and environmental advocates for urgent action to address air pollution.
People living in areas where the air contains higher levels of nitrogen dioxide, nitrogen oxides and other harmful particulate matter were at greater risk for being diagnosed with depression or anxiety over the course of the study. The nitrogen contaminants primarily get into the air from the burning of fuel, including from emissions produced by vehicles and power plants.
Notably, the results pointed to elevated anxiety and depression risk even at levels of air pollution considered acceptable by UK air quality standards, according to the study, which was published in the Journal of the American Medical Association (JAMA) Psychiatry.
“Our findings warrant that more strict air quality standards on a globe scale should be adopted based on the new [World Health Organization (WHO)] guidelines to alleviate the disease burden of depression and anxiety related to multiple air pollutants,” Jing Huang and Guoxing Li, researchers at the Peking University Health Science Center in China and two authors of the study, said in an email to The New Lede.
The fact that researchers found mental health effects at air pollution levels considered safe by both the UK and US governments is particularly worrisome, according to Clara Zundel, a postdoctoral researcher at Wayne State University in Michigan and an author of a recent review on air pollution and mental health.
“The first thing that jumped out at me was that [the authors] are actually finding effects at much lower levels of air pollution than have previously been reported,” Zundel said.
The current US Environmental Protection Agency (EPA) standards for concentrations of particulate matter with diameters of 2.5 micrograms or less (PM 2.5) is currently 12 micrograms per cubic meter. While the agency recently proposed strengthening those measures by reducing the standard to 9 to 10 micrograms per cubic meter, the study’s findings suggest even this might not be low enough.
“This specific study is actually still finding effects, specifically on mental health, at that 9 to 10 level in particulate matter, which I think is really interesting,” said Zundel.
The study’s analysis of mental health effects over the course of ten years “speaks to the fact that it’s not just effects in mental health right after you’re exposed [to air pollution],” said Zundel. “It might take a long time to actually see those effects.”
Adding to the evidence
Growing evidence has linked air pollution, a major problem worldwide, to mental health effects, with some studies finding that short-term exposure to air pollution is associated with increased risk of hospitalization for mental health disorders. However, Huang and Li noted that previous studies on the long-term mental health effects of air pollution exposure have produced conflicting findings. Additionally, they said that previous studies on air pollution and depression risk in the general population were conducted in regions with pollution levels that exceeded UK air quality standards.
“We conducted this study in a UK population in which the actual air pollution level is below the UK air quality standard, to explore whether long-term exposure to air pollution at low levels would cause increased risk of incident depression and anxiety disorders,” said Huang and Li. “We considered not only the association of single air pollutants, but also the joint exposure to multiple air pollutants to evaluate the comprehensive influence.”
Between 2006 and 2010, the team drew from the UK Biobank, a massive biomedical database, to collect baseline data on participants’ social and demographic factors, lifestyles, and health. From 2010 to 2020, they monitored the participants’ health, finding that about 13,000 were diagnosed with depression and almost 16,000 were diagnosed with anxiety.
“I think this study did an excellent job of really trying to isolate the impact of air pollution on mental health,” said Zundel. “They used this huge cohort that had a lot of additional data that helped them control for things like neighborhood characteristics, like if people lived closer to a highway versus if they lived in the country, and socioeconomic [factors] that impact our health beyond air pollution.”
Zundel added that models like those used in the study are somewhat limited, since they base their air pollution data on people’s residential addresses, where people only tend to spend a portion of their time. She also noted that the study solely looked at adults, saying that research that takes a “lifespan approach” can shed light on the mental health effects of air pollution in childhood, adolescence, and old age.
“The next step that’s missing in this research is we don’t really know how this is happening within the brain,” said Zundel. “How does air pollution affect our brains in a way that it increases our risk for mental health issues?”