All of us have had nights where we simply can’t fall asleep no matter how hard we try, or mornings where we woke up feeling like we barely slept a wink. Was it the late night coffee, the noisy neighbours, or the air conditioning temperature that we just never seem to get right? Aside from these reasons that often come to mind, air pollution could very well be the culprit of poor sleep quality. On average, over 34% of adults sleep less than 7 hours a night (Yu et al., 2019). How might air pollution be responsible? Let’s find out.
Air pollutants cause reductions in sleep duration and sleep quality (proportion of time spent asleep in bed as compared to being awake) by irritating key organs of the human respiratory system. In addition, pollutants in the bloodstream negatively affect brain activity and breathing regulation (Davis, 2017).
It is no surprise then, that Yu et al. (2019) discovered a negative relationship between air pollution levels and the sleep duration of university freshmen in China. A one standard deviation increase in AQI translates to 0.68 less hours of sleep. Figure 1 illustrates that sleeping hours are generally lower when AQI is higher. Specifically, survey time 3 shows a huge decline in sleeping hours when AQI increased by 3 levels. When AQI decreased by 2 levels in the next survey time, sleeping hours increased by nearly 1 hour.
Figure 1. Trend between sleep duration (hours per day) and AQI levels among university freshmen in China (Yu et al., 2019)
Another study by Haberzettl (2018) explores the impacts of air pollution on the circadian rhythm of our bodies. Circadian rhythms are defined as internally driven cycles throughout the 24-hour day that induce sleep at night and wake us up in the morning (NIOSH, n.d.). According to Haberzettl (2018), air pollutants induce “oxidative stress” which in turn disrupts our natural circadian clocks by altering clock protein activity. Not only does this “oxidative stress” disrupt our sleep cycle, it also diminishes nocturnal systolic blood pressure dip, which is in turn associated with increased risk of cardiovascular diseases and mortality.
Figure 2. Mechanisms of oxidative stress induced by air pollution (Haberzettl, 2018)
Finally, air pollution is also a cause of sleep apnea, a common sleep disorder in which breathing ceases and restarts while one is asleep, depleting the body of sufficient oxygen (NIH, n.d.). Even though the typical causes of sleep apnea are related to factors such as weight, gender, age, and lifestyle habits (Mayo Clinic, 2022), Billings et al. (2019) found that higher levels of NO2 and PM2.5 exposure make individuals more prone to sleep apnea. Interestingly, however, the study noted that long-term (5 year) exposure to PM2.5 seemed to reduce the odds of contracting sleep apnea as opposed to short-term (1 year) exposure (Figure 3). The authors cited “chronic adaptation” as a possible explanation, which ties in well with the idea of Circadian rhythms highlighted earlier. Yet, this then begs the question of why the same effect is not observed for NO2 exposure.
Figure 3. Adjusted odds of obstructive sleep apnea with respect to increased exposure to ambient air pollution (Billings et al., 2019)
It is deeply worrying that the harmful effects of air pollution follow us into the cozy confines of our bedroom, stealing what little precious sleep time we have. Not only that, they heighten our risk of developing various health complications as we sleep – which is pretty ironic, given that sleep is meant to let our bodies recover. If we’re not curbing air pollution to prevent further harm to ourselves, we should at least be doing it to ensure that the sleep-induced healing is not impeded.
Until the next entry, breathe safe and be safe!
References
Billings, M. E., Gold, D., Szpiro, A., Aaron, C. P., Jorgensen, N., Gassett, A., Leary, P. J., Kaufman, J. D., & Redline, S. R. (2019). The association of ambient air pollution with sleep apnea: The multi-ethnic study of Atherosclerosis. Annals of the American Thoracic Society, 16(3), 363–370. https://doi.org/10.1513/annalsats.201804-248oc
Davis, N. (2017, May 21). Air pollution linked to poor sleep, study finds. The Guardian. Retrieved March 7, 2023, from https://www.theguardian.com/lifeandstyle/2017/may/21/air-pollution-linked-to-poor-sleep-study-finds
Mayo Foundation for Medical Education and Research. (2022, December 23). Sleep apnea. Mayo Clinic. Retrieved March 7, 2023, from https://www.mayoclinic.org/diseases-conditions/sleep-apnea/symptoms-causes/syc-20377631
National Heart, Lung, and Blood Institute. (n.d.). What is sleep apnea? What Is Sleep Apnea? Retrieved March 7, 2023, from https://www.nhlbi.nih.gov/health/sleep-apnea
The National Institute for Occupational Safety and Health. (n.d.). Circadian rhythms and circadian clock. Circadian Rhythms and Circadian Clock. Retrieved March 7, 2023, from https://www.cdc.gov/niosh/emres/longhourstraining/clock.html
Palanivel, R., Vinayachandran, V., Biswal, S., Deiuliis, J. A., Padmanabhan, R., Park, B., Gangwar, R. S., Durieux, J. C., Ebreo Cara, E. A., Das, L., Bevan, G., Fayad, Z. A., Tawakol, A., Jain, M. K., Rao, S., & Rajagopalan, S. (2020). Exposure to air pollution disrupts circadian rhythm through alterations in chromatin dynamics. IScience, 23(11), 101728. https://doi.org/10.1016/j.isci.2020.101728
Yu, H., Chen, P., Paige Gordon, S., Yu, M., & Wang, Y. (2019). The association between Air Pollution and sleep duration: A cohort study of freshmen at a university in Beijing, China. International Journal of Environmental Research and Public Health, 16(18), 3362. https://doi.org/10.3390/ijerph16183362