Are Smoggy Skies Leading to Smoggy Minds?

It's no surprise that air pollution is bad for our lungs. But a new meta-analysis suggests it could also be heightening our risk of dementia.


Scientists have long known that long-term exposure to air pollution isn’t good for the lungs — it can irritate the respiratory system and even cause lung cancer. But a recent study has demonstrated that air pollution may even affect our brains. Specifically, there may be an association between high exposure to air pollutants and dementia risk.

What is dementia?

Dementia is the umbrella term used to describe cognitive decline (e.g., impairments to thinking and remembering). It develops in many people 65 years and older worldwide.

The most common type of dementia is Alzheimer’s disease, but dementia also encompasses other types of conditions such as vascular dementia and frontotemporal lobe dementia.

Effects of air pollution on the brain

Previous research has illustrated that pollutant exposure causes an inflammatory response in the brain, a response that typically occurs when the brain is injured or infected. Furthermore, air pollutants have been associated with an altered immune response and Alzheimer’s disease-like brain pathology. All of these negative outcomes of air pollution can also cause declines in cognition, and thus a diagnosis of dementia.

However, the pollution in the air differs across the globe. Some geographical regions have higher air pollutants than others, and there are different types of pollutants found in different regions.

For this reason, Dr. Ehsan Abolhasani and colleagues from Western University set out to examine the results from scientific studies conducted in different geographical regions around the globe that looked at long-term exposure of different air pollutants and its association with the frequency of dementia diagnoses. Their systematic review and meta-analysis paper was published in Neurology.

What did they find?

The team looked at 17 different studies that investigated the association of higher levels of air pollution exposure with dementia in adults over 40 years of age. Between one and five air pollutants were measured across each of the studies, including particulate matter, nitrogen oxides, nitrogen dioxide, nitrogen monoxide, and ozone. The studies were conducted in different geographical regions within North America, Europe, and Asia.

Overall, the team found significant associations between increased exposure to particulate matter pollutants (e.g., matter emitted from construction sites or wood burning) and the frequency of dementia diagnoses. In addition, higher exposure to nitrogen dioxide (e.g., pollution from road traffic or fossil fuel processes) was significantly associated with the incidence of dementia.

Therefore, based on results from these studies, high levels of exposure to air pollutants typically produced in large cities (particulate matter and nitrogen dioxide pollutants) are associated with a greater rate of dementia diagnoses in these regions.

It’s clear that air pollution is not only negatively affects our lungs but also impacts our brain health in some way shape, or form. In particular, air pollution specifically impacts the aging population in many regions around the world.

Perhaps knowing this — and knowing that our brain is a body part that cannot be replaced, like our heart or lungs — we will start to make more environmentally friendly habits. In turn, this could help decrease the chances of cognitively declining in the future.

A take-home message from this systematic review and meta-analysis paper may be: go green to stay sharp!

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Alexandria (Alex) Samson is a PhD student in the Department of Psychology at the University of Toronto. She completed her BSc in Neuroscience from Dalhousie University. Alex is a strong believer in open science and is passionate about making scientific research accessible to all audiences.