January 24, 2020, by sbzaj1

How bad is air pollution for our brain?

Written by Sakaorna Jeyanathan

Nobody can deny that we are globally subjected to air pollution on a daily basis. Although it may not be as drastic as the pollution in China(1), we have unknowingly become accustomed to the fumes produced by cars, factories and agriculture(2). Presumably, this can have severe implications on our respiratory system in the long run. However, recent research has reported that this can also impact our brain(3). Scientists have proposed that air pollution is a potential environmental factor that can cause the dysfunction of the brain, such as brain tissue deterioration and cognitive decline. The exposure of a certain form of particulate matter (PM) of diameter 2.5 micrometres (PM2.5) has been recently discovered to increase the risk of Alzheimer’s. Indeed, previous studies have associated PM to the induction of brain tumours and other forms of dementia(4). This article will review how harmful particulate matter is to the brain, reinforcing the need to reduce air pollution.

Air pollution is a combination of chemicals such as ozone, carbon monoxide, nitrogen oxide and other organic compounds and metals. A certain form of air pollutant called particulate matter (PM), has been recognised to cause harm to the human brain. PM can range from 2.5-10 micrometres in diameter and consists of smoke and dust(3) and are commonly used as a marker to evaluate the pollution in a certain area. Recent papers have discovered that PM can accumulate in the brain, via inhalation or directly through the nose via the olfactory nerve(4).

The aforementioned US research team that discovered this association between PM2.5 to Alzheimer’s was noteworthy, as although previous studies has recognised an association with PM to Alzheimer’s, it was unknown how these particles altered the neurobiology of the brain. This study examined whether PM2.5 can increase the risk of Alzheimer’s by analysing brain scans of women from the ages of 73 to 87 who were scanned twice every five years from 1993(5). An algorithm was created which could analyse brain patterns similar to that of an Alzheimer’s patient. After removing factors such as race, education and smoking, the study could find an association between high exposure to pollution and the decline in areas of the brain associated with memory such as the hippocampus(6). The study suggests that these particles induce neurotoxicity in areas of the brain, leading to memory decline.

These studies highlight that air pollution is not only an environmental issue but also affects our human population. Surprisingly in the UK, PM2.5-10 has decreased immensely from 1992 to 2018. Research has also proposed that these particles could relate to other dysfunctions of the brain such as malignant brain tumours(4). However, Public Health England has estimated that 28,000 – 36,000 deaths may be related to long term exposure to air pollution(2), reinforcing the need to lower pollution. This finding simultaneously provides a promising lead to the discovery of an intervention to help patients with Alzheimer’s and other cognitive and memory related neurological diseases.

1. Kao, E. Air pollution is killing 1 million people and costing Chinese economy 267 billion yuan a year, research from CUHK shows. South China Morning Post 267 (2018).

2. Public Health England. Health matters: air pollution – GOV.UK. (2018).

3. Paul, K. C., Haan, M., Mayeda, E. R. & Ritz, B. R. Ambient Air Pollution, Noise, and Late-Life Cognitive Decline and Dementia Risk. Annu. Rev. Public Health 40, 203–220 (2019).

4. Andersen, Z. J. et al. Long-term exposure to ambient air pollution and incidence of brain tumor: The European Study of Cohorts for Air Pollution Effects (ESCAPE). Neuro. Oncol. 20, 420–432 (2018).

5. News, N. & News, N. Exposure to PM 2 . 5 pollution linked to brain atrophy and memory decline.

6. Younan, D. et al. Particulate matter and episodic memory decline mediated by early neuroanatomic biomarkers of Alzheimer ’ s disease. (2019).

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