Air pollution, depressive and anxiety disorders, and brain effects: A systematic review

Abstract

Accumulating data suggest that air pollution increases the risk of internalizing psychopathology, including anxiety and depressive disorders. Moreover, the link between air pollution and poor mental health may relate to neurostructural and neurofunctional changes. We systematically reviewed the MEDLINE database in September 2021 for original articles reporting effects of air pollution on 1) internalizing symptoms and behaviors (anxiety or depression) and 2) frontolimbic brain regions (i.e., hippocampus, amygdala, prefrontal cortex). One hundred and eleven articles on mental health (76% human, 24% animals) and 92 on brain structure and function (11% human, 86% animals) were identified. For literature search 1, the most common pollutants examined were PM_2.5 (64.9%), NO₂ (37.8%), and PM₁₀ (33.3%). For literature search 2, the most common pollutants examined were PM_2.5 (32.6%), O₃ (26.1%) and Diesel Exhaust Particles (DEP) (26.1%). The majority of studies (73%) reported higher internalizing symptoms and behaviors with higher air pollution exposure. Air pollution was consistently associated (95% of articles reported significant findings) with neurostructural and neurofunctional effects (e.g., increased inflammation and oxidative stress, changes to neurotransmitters and neuromodulators and their metabolites) within multiple brain regions (24% of articles), or within the hippocampus (66%), PFC (7%), and amygdala (1%). For both literature searches, the most studied exposure time frames were adulthood (48% and 59% for literature searches 1 and 2, respectively) and the prenatal period (26% and 27% for literature searches 1 and 2, respectively). Forty-three percent and 29% of studies assessed more than one exposure window in literature search 1 and 2, respectively. The extant literature suggests that air pollution is associated with increased depressive and anxiety symptoms and behaviors, and alterations in brain regions implicated in risk of psychopathology. However, there are several gaps in the literature, including: limited studies examining the neural consequences of air pollution in humans. Further, a comprehensive developmental approach is needed to examine windows of susceptibility to exposure and track the emergence of psychopathology following air pollution exposure.

Keywords: Air pollution; Anxiety; Brain; Depression; Frontolimbic; Mental health.

Figure 1.

Flowchart for Literature Search 1 and 2. Panel A describes Literature Search 1: Air Pollution and Internalizing Behaviors and Symptoms. Panel B describes Literature Search 2: Air Pollution and Frontolimbic Brain Regions Each step of the reviews was informed by PRISMA guidelines (Page et al., 2021).

Figure 2.

Publications by Year for Literature Searches 1 (A) and 2 (B).

Figure 3.

Summary of Study Types for Literature Searches 1 (blue) and 2 (green). Panel A – Populations Examined by Species, Panel B – Populations Examined by Sex, Panel C – Exposure Windows Examined Panel D – Exposure Methods for Animal Studies, Panel E – Exposure Methods for Human Studies

Figure 4.

Map of Locations of Human Observations Studies for each Literature Search. Panel A – Literature Search 1 – Internalizing Symptoms & Behaviors, Panel B – Literature Search 2 – Frontolimbic Brain Regions

Figure 5.

A conceptual model of neurobehavioral mechanisms by which air pollution exposure increases risk of internalizing psychopathology through structural and functional changes in frontolimbic brain regions. This figure was created with BioRender.com.