Evidence has been building for years that air pollution increases the risk of heart and respiratory diseases and reduces lifespan, but much less is known about how it impacts the brain.

That’s changing.

Now, two new studies reveal deeply troubling evidence of the effects of air pollution on the brain.

Not only does air pollution appear to speed up the production of brain plaques, but even “safe” levels of pollution can increase the risk of Alzheimer’s and Parkinson’s diseases.

Researchers from Harvard T.H. Chan School of Public Health conducted a massive population study to examine the effects of particulate matter 2.5 (PM2.5) on the brain.

PM2.5 is the category for air pollutants that result from burning gasoline, diesel, wood or coal. These particles are extremely small, less than 1/30th the width of a human hair, are easily inhaled and are believed to pose the greatest risk to health.

More Pollution Equals More Memory Damage

For their study, published in the journal The Lancet Planetary Health in October, the Harvard research team tracked over 63 million individuals aged 65 or older for more than 17 years and recorded the pollution levels in their zip codes.

During the period, a million people were admitted to the hospital for the first time for Parkinson’s while 3.4 million had their first hospital admission for Alzheimer’s.

After taking into account many factors that can lead to these conditions, the study team found that for each five micrograms per cubic meter of air (5μg/m3) increase in annual PM2.5 concentrations, there was a 13 percent increase in the risk of first hospital admission for both Parkinson’s and Alzheimer’s.

Even more alarming, this was the case “even at concentrations less than the current annual national standards (12μg/m3),” they wrote.

They concluded that the study provides strong evidence that long-term exposure to air pollution even at low levels is linked to deteriorating brain health.

While highly indicative, this study cannot prove beyond doubt that pollution causes these effects. Stronger evidence for causation is needed, and another recent study provided more of it.

Increases Brain Plaques by Ten Percent

A large research team led by the University of California, San Francisco (UCSF) enrolled 18,176 patients with an average age of 75 who had been diagnosed with either dementia or mild cognitive impairment (MCI), which often precedes the onset of dementia.

Each underwent a PET scan to look for deposits of beta-amyloid brain plaques. In addition, the researchers recorded air pollution levels in the communities where participants lived at the time of the scan as well as 14 years earlier.

After accounting for many factors that could skew their analysis, they found those living in the most polluted areas 14 years ago were ten percent more likely to have brain plaques than those living in the least polluted areas.

One of the study authors, Gil Rabinovici, commented, “This study provides additional evidence to a growing and convergent literature, ranging from animal models to epidemiological studies, that suggests air pollution is a significant risk factor for Alzheimer’s disease and dementia.”

Dr. Leonardo Iaccarino, who was the first author of the UCSF study, believes the research shows that air pollution has direct effects on the brain.

Promotes Neuro-inflammation

“Exposure in our daily lives to PM2.5, even at levels that would be considered normal, could contribute to induce a chronic inflammatory response,” explains Dr. Iaccarino.

“Over time, this could impact brain health in a number of ways, including contributing to an accumulation of amyloid plaques.”

Xiao Wu, who was part of the previous Harvard study, described the UCSF finding as “important” because it links the biology of Alzheimer’s to air pollution. He agrees that pollution has direct effects on the brain.

It’s important to note that several types of pollutant, not just PM2.5, have been shown to easily cross the blood-brain barrier. For this reason, it’s highly likely these results are the tip of the iceberg. As we learn more, we’ll probably see that a much broader range of pollutants give rise to neurodegenerative diseases and/or accelerate the decline in existing conditions by directly contributing to inflammatory processes in the brain.

Linked to Memory Loss

In addition, the Harvard and UCSF studies are not the only studies to confirm a link between air pollution and cognitive decline.

A growing number of studies have linked air pollution to impaired cognitive function, accelerated cognitive decline, Parkinson’s, Alzheimer’s and other dementias.

For instance, in a research review published in 2016, researchers concluded that the evidence “provides support for a relation of air pollution exposure to dementia.”

These are findings we should take seriously.

Anyone living in polluted cities should consider what they can do to cut back on their exposure to air pollution, whether it’s buying home air purifiers or moving to rural areas. With the coronavirus, many people have shifted to working from home, so moving into the countryside becomes possible. In fact, such COVID-driven migration out of big cities has already begun.


  1. https://pubmed.ncbi.nlm.nih.gov/27328897/ 
  2. https://www.thelancet.com/journals/lanplh/article/PIIS2542-5196(20)30227-8/fulltext 
  3. https://jamanetwork.com/journals/jamaneurology/article-abstract/2773645 
  4. https://www.ucsf.edu/news/2020/11/419141/forest-fires-cars-power-plants-join-list-risk-factors-alzheimers-disease 

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