Even Low Levels of Air Pollution Could Be Bad for Mental Health

Long-term exposure to air pollution may be a driver of mental health issues, a prospective cohort study suggested.

In an analysis of nearly 400,000 people in the U.K., long-term exposure to various air pollutants were linked with a higher risk for incident depression and anxiety, reported Jing Huang, PhD, of the Peking University School of Public Health in Beijing, and colleagues.

Compared with the lowest quartile of air pollution score, those falling into the second, third, and fourth quartiles had a significant 8%, 17%, and 16% higher risk for incident depression, respectively, they stated in JAMA Psychiatry.

Likewise, people falling into the second, third, and fourth quartiles for air pollution score had 9%, 14%, and 11% higher risks for developing anxiety compared with people in the lowest quartile over the 11-year follow-up.

Air pollution score was based on combined exposure to small particulate matter with aerodynamic diameter of 2.5 μm or less (PM_2.5), nitrogen dioxide (NO₂), and nitric oxide (NO). Particulate pollution is often in the form of dust or smoke and can be small enough where its naked to the eye. NO₂ and NO pollution often comes from car, power plant emissions, and other sources of burning gas.

Models in the study were adjusted for age, sex, ethnicity, level of deprivation, length of time at residence, and more.

Even at relatively low levels of exposure, all three of these air polluters were individually tied with depression and anxiety.

First looking just at PM_2.5 exposure, higher levels of exposure showed significantly increased risks for incident depression compared with the lowest quartile of exposure, representing pollutant level less than 9.3 μg/m³:

• 9.3-9.9 μg/m³: HR 1.09 (95% CI 1.03-1.14)
• 9.9-10.6 μg/m³: HR 1.14 (95% CI 1.08-1.20)
• 10.6 μg/m³ or more: HR 1.15 (95% CI 1.08-1.21)

In a subgroup analysis, the link between PM_2.5 exposure and anxiety was higher for males in the highest quartile of pollutant levels at HR 1.18 (95% CI 1.08-1.29) versus HR 1.07 (95% CI 1.00-1.14) for females.

The same pattern was seen at all higher levels of NO₂ exposure compared with the lowest quartile of exposure, representing a pollutant level less than 21.3 μg/m³:

• 21.3-26.0 μg/m³: HR 1.11 (95% CI 1.06-1.17)
• 26.0-31.1 μg/m³: HR 1.15 (95% CI 1.09-1.22)
• 31.1 μg/m³ or more: HR 1.14 (95% CI 1.07-1.21)

And the same was also seen for NO exposure at the higher quartiles versus the lowest quartile of less than 11.6 μg/m³:

• 11.6-15.9 μg/m³: HR 1.07 (95% CI 1.02-1.13)
• 15.9-20.6 μg/m³: HR 1.11 (95% CI 1.06-1.17)
• 20.6 μg/m³ or more: HR 1.12 (95% CI 1.06-1.18)

Nearly identical patterns were seen in terms of new anxiety cases, with steep inclines between the first and second quartiles of exposure, then plateauing through the fourth quartile, the authors reported.

For context, median concentration of pollutants were 9.9 μg/m³ for PM_2.5, 26.0 μg/m³ for NO₂, and 15.9 μg/m³ for NO — all high enough to be significantly linked to a higher risk for depression or anxiety.

Huang’s group pointed out that these increased associated risks for depression and anxiety were both seen at concentration levels below the annual values in U.K. air quality standards.

While they called for more research to better understand the mechanisms behind how air pollution may up the risk for these mental burdens, they suggested that it could be due to the way the pollutant affects the central nervous system thru inflammatory and oxidative stress.

Data for the study came from the U.K. Biobank and participants were recruited from 2006 to 2010. Of the 389,185 participants (mean age 56.7; majority female and white), 13,131 were diagnosed with depression and 15,835 were diagnosed with anxiety according to ICD-10 codes.

“Considering that many countries’ air quality standards are still well above the latest World Health Organization global air quality guidelines 2021, stricter standards or regulations for air pollution control should be implemented in the future policy making,” Huang and colleagues advised, adding that the current “results may provide important evidence for the assessment of mental health associated with air pollution to be considered in the Global Burden of Disease.”