Air pollution has a history of going unnoticed or underestimated in its capacity to cause harm. However, a recent study by Teng Yang and colleagues published in JAMA Psychiatry brings attention to the potential danger of air pollutants as exposure becomes increasingly likely, especially for minority groups and low-income families.
“In this cohort study of 389,185 participants, estimated joint exposure to multiple air pollutants was associated with increased risk of depression and anxiety,” the authors write. “Air pollution is increasingly recognized as an important environmental risk factor for mental health. However, epidemiologic evidence on long-term exposure to low levels of air pollutants with incident depression and anxiety is still very limited.”
The authors focused on two air pollutants for this study: nitrogen dioxide (NO2) and nitric oxide (NO). These are referred to as NOX pollutants. They are commonly found in vehicle exhaust emissions and industrial facilities like power plants. The researchers hypothesized an association between long-term exposure to these NOX pollutants and incident depression and anxiety.
Participants had never been diagnosed with depression or anxiety before the start of the study, and their exposure to air pollution was found using data from the UK Biobank. A method known as a land use regression model was employed for this study.
A land use regression model, or a LUR, is common for studies like this one because they assess pollution patterns. They are especially useful in densely populated areas. In essence, a LUR combines information from land usage statistics and significant geography/landmarks, such as roads and proximity to significant sources of pollution. Meteorological history and terrain from satellite data are used to create a heat map of pollution. Multiple maps can be made to represent the passage of time and the change in air pollutant volume.
Of the 389,185 participants in this study, 13,131 were diagnosed with depression, and 15,835 were diagnosed with anxiety. Perhaps especially alarming was the discovery that only a small exposure to these air pollutants led to an increased likelihood of diagnosis for either depression or anxiety, and more severe exposures created a plateau in diagnosis likelihood. This suggests a binary effect rather than a spectrum of severity. Exposure to NO2 and NO increases the incidence of depression and anxiety, and it is not strongly moderated by the harshness of the exposure.
The authors stress the importance of this latter discovery as it could have policy implications. Mitigating air pollution won’t necessarily be enough to solve the issue—NO2 and NO can cause damage, even in low amounts. To solve the issue, air pollution must be reduced, making long-term exposure impossible. This problem is more urgent for lower-income communities of color because they are disproportionately exposed to such air pollution.
This study can be examined with past research that made similar findings. For example, Mary Abed Al Ahad corroborates the findings of Teng Yang and says, “Clearly, environmental policies to reduce air pollution emissions can eventually improve the mental well-being of the UK’s population.”
In 2016, a then-new article from researchers in Sweden discovered a link between the concentration of air pollution and the number of psychiatric drugs prescribed to children. This link was still observed, “even at pollution levels well below half of what is considered acceptable by the World Health Organization.”
All of this is to say that air pollution is another risk factor for depression and anxiety that minority populations, especially people of color, face disproportionately. And these comparable studies from more than five years ago show the lack of progress in defending vulnerable populations from an undue mental health burden.
The authors highlight the importance of being aware of sources of air pollution, but worsening disregard for the climate and the general pervasiveness of cars represent a cause for concern. On an individual level, decreasing proximity to car exhaust and filtering indoor air are sound methods of reducing one’s risk of NOX exposure.
Yang, T., Wang, J., Huang, J., Kelly, F. J., & Li, G. (2023). Long-term Exposure to Multiple Ambient Air Pollutants and Association With Incident Depression and Anxiety. JAMA Psychiatry. https://doi.org/10.1001/jamapsychiatry.2022.4812 (Link)