air pollution alzheimer's

Air Pollution May Lead to a Key Alzheimer’s Biomarker in the Brain

By Vipul Kamani | December 10th, 2020

Air pollution — a major cause of global warming — has been on the forefront of the debate regarding climate change. Now, as we arrive at the fifth anniversary of the Paris Agreement, the Lancet Countdown has published a concerning report produced by dozens of the world’s leading climate change and pollution experts from academia and a number of United Nations agencies, outlining the crisis. According to the authors, 2020 indicators present the most worrying outlook since the Lancet Countdown was established in 2016.

The report comes hot on the heels of a recent study conducted by Leonardo Iaccarino, a postdoctoral scholar at the UCSF Weill Institute for Neuroscience, and colleagues. It adds to the abundance of research that suggests a link between exposure to air pollution and the risk of developing Alzheimer’s disease.

Iaccarino said that the fine particulate matter known as PM2.5 — a type of air pollutant — can play a role in triggering long-term inflammation, and in turn, stimulate the buildup of beta-amyloid plaques in the brain. 

“Exposure in our daily lives to PM2.5, even at levels that would be considered normal, could contribute to induce a chronic inflammatory response,” he said in a news release. “Over time, this could impact brain health in a number of ways, including contributing to an accumulation of amyloid plaques.”

In the current study, researchers examined a group of 18,178 individuals, with an average age of 75, who had received a diagnosis of mild cognitive impairment or dementia. They compared PET scans between 2016 and 2018 to the participants’ residence air quality index in years 2002-03 and 2015-16. 

What the researchers found was a significant difference — an increase of about 10 percent — in the likelihood of developing beta-amyloid plaques in participants who lived in areas with the highest PM2.5 concentrations, when compared to those who lived in areas with the lowest levels of the pollutant. Consequently, the researchers concluded that there is a significant correlation between airborne pollutants and the risk of developing beta-amyloid plaques. 

These findings are in accordance with research published in the past. A 2019 study at the University of Southern California also found visible changes — particularly atrophy — in the brains of women who had experienced greater levels of air pollution. 

In an interview with Being Patient, Andrew Petkus, author of the study and professor of Neurology at USC, explained, “There are a few hypotheses [about how air pollution may lead to plaques]. One is that not only does the particulate matter go into your lungs, but it goes into your bloodstream and reaches your brain that way. When we directly inhale it through our nose, it can go directly into the brain.” 

Further, he highlighted how the presence of this particulate matter in the brain caused inflammation in the brain, as shown in past studies involving mice. 

What’s more, a 2018 study, which was part of the London Traffic Project, found that people living in areas with the highest levels of NO2 — another toxic air pollutant — were 40 percent more likely to receive a dementia diagnosis. Similar results were obtained for PM2.5. Further, there appeared to be a particularly significant correlation between pollution and Alzheimer’s, as opposed to the other forms of dementia. 

However, the community must be vary of generalizing correlations to causation. James Pickett, Head of Research at the Alzheimer’s Society, highlighted this fact. “Air pollution is a hot topic in dementia research, and there is evidence that exposure to air pollution can cause small particles to enter the brain, but it’s a huge leap to say that air pollution could lead to dementia,” he told Being Patient. 

While the definite proof of causation remains elusive, the authors of the current study concluded, “These findings suggest the need to consider airborne toxic pollutants associated with beta-amyloid pathology in public health policy decisions and to inform individual lifetime risk of developing AD [Alzheimer’s Disease] and dementia.”

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