Mental health is increasingly the talk of the town as modern lifestyles become more fast-paced and intensive. Despite growing awareness of the need to actively care for one’s mental health through various means, one cause of poor mental health is nearly impossible to evade – air pollution.
In an earlier post, I mentioned how air pollution is responsible for 7 million global deaths annually. Today, I found out that mental disorders affect over 300 million people and that this figure rose by more than an astonishing 18% between 2005 and 2015 (Ali and Khoja, 2019). In this entry, let us explore the relationship between air pollution and mental health in greater depth.
According to Zundel et al. (2022), air pollution is associated with greater risk of “internalizing disorders” like anxiety and depression. This is especially worrying, given that much of the world’s population is living in places with air quality deemed to be unsafe by the World Health Organization. A spatial study conducted by Khan et al. (2019) in the US illustrated the effects of air quality on the incidence rate of various mental disorders. While there is no clear association between air quality and personality disorder, there is a visible relationship between air quality and the other five types of mental disorders. Incidence rates of mental disorders are typically lowest in the central US, and the observed increase towards the eastern and western regions correspond with deteriorating air quality shown in Figure 1. Figure 2 highlights an especially pronounced trend between poor air quality and incidence of major depression – and this got me wondering why.
Figure 1. Map of spatial variations in air quality in US counties (Khan et al., 2019)
Figure 2. Map of spatial variations in mental disorder incidence rates in US counties (Khan et al., 2019)
From a medical perspective, air pollution has been shown to be associated with neuroinflammation, oxidative stress, and cerebrovascular damage, all of which are known inducers of depression (Borroni et al., 2022). In the same study, the authors found that the increase in risk of depression due to a 10 μg/m3 increase in PM2.5, NO2. and CO concentrations were 7%, 4%, and 6% respectively. In fact, the pervasiveness of air pollution indicates that mental disorders like depression may persist even if the stress tied to urban lifestyles were to be hypothetically removed (Carrington, 2020).
Figure 3. Conceptual model of how air pollution exposure increases risk of internalizing psychopathology (Zundel et al., 2022)
Another study by Hautekiet et al. (2022) investigates the effects of black carbon (BC), PM2.5, and NO2 on the odds of developing various mental disorders. Though the results unsurprisingly indicate greater likelihood of developing most mental disorders as a result of exposure to the selected air pollutants, there is a key difference between this study and that of Zundel et al. (2022) that I must point out. In the latter, the relationship between air pollution and mental health appeared to be drawn directly based on the spatial correlation between air quality and incidence rates of mental disorders. On the other hand, the former study accounted for significant confounders such as physical activity which is generally beneficial to mental health. Hence, the results obtained represent the additional likelihood of developing mental disorders regardless of external circumstances, thereby clearly reflecting air pollution’s detriments to mental health.
Figure 4. Odds ratios of all mental health dimensions and self-rated health given an increment in PM2.5, NO2, or BC concentrations (Hautekiet et al., 2022)
I suspect that the relationship between air pollution and mental health is not as well-known as it should rightfully be; and that is exactly what makes air pollution dangerous. Air pollution is mentally damaging even in the slightest of doses; its effects on a larger scale and across longer periods would be unfathomable. I hope that this aspect of air pollution will soon be recognized, spurring swift and decisive action towards improving the quality of air we breathe.
Until the next entry, breathe safe and be safe!
References
Ali, N. A., & Khoja, A. (2019). Growing evidence for the impact of air pollution on depression. Ochsner Journal, 19(1), 4–4. https://doi.org/10.31486/toj.19.0011
Borroni, E., Pesatori, A. C., Bollati, V., Buoli, M., & Carugno, M. (2022). Air Pollution Exposure and depression: A comprehensive updated systematic review and meta-analysis. Environmental Pollution, 292, 1–27. https://doi.org/10.1016/j.envpol.2021.118245
Carrington, D. (2020, October 24). Small increases in air pollution linked to rise in depression, finds study. The Guardian. Retrieved February 28, 2023, from https://www.theguardian.com/environment/2020/oct/24/small-increases-in-air-pollution-linked-to-rise-in-depression-finds-study
Hautekiet, P., Saenen, N. D., Demarest, S., Keune, H., Pelgrims, I., Van der Heyden, J., De Clercq, E. M., & Nawrot, T. S. (2022). Air pollution in association with mental and self-rated health and the mediating effect of physical activity. Environmental Health, 21(1), 1–13. https://doi.org/10.1186/s12940-022-00839-x
Khan, A., Plana-Ripoll, O., Antonsen, S., Brandt, J., Geels, C., Landecker, H., Sullivan, P. F., Pedersen, C. B., & Rzhetsky, A. (2019). Environmental pollution is associated with increased risk of psychiatric disorders in the US and Denmark. PLOS Biology, 17(8), 1–28. https://doi.org/10.1371/journal.pbio.3000353
Zundel, C. G., Ryan, P., Brokamp, C., Heeter, A., Huang, Y., Strawn, J. R., & Marusak, H. A. (2022). Air Pollution, depressive and anxiety disorders, and brain effects: A systematic review. NeuroToxicology, 93, 272–300. https://doi.org/10.1016/j.neuro.2022.10.011