The missing link between air pollution and brain health

The latest research programme between the universities of Luxembourg, Bonn and Rostock has uncovered an important correlation between air pollution particles and neurological diseases.

The head researcher behind the project, Dr Benjamin Aretz from the University of Bonn, discusses the reasons behind the study and the impact it can have on how we tackle air pollution at this critical moment in the climate crisis.

The dangers of fine particulate matter

The project focused on fine particulate matter, known as PM2.5, which Aretz, a postdoctoral researcher focusing on demography, health data science, and epidemiology, describes as “very small particles or droplets in the air that are 2.5 micrometres or smaller in diameter – roughly 30 times smaller than the diameter of a human hair.”

These particles are emitted from numerous sources such as “vehicles, industrial processes, wildfires, and residential heating,” said Aretz.

Fine particulate matter can cause negative repercussions on the human body, with Aretz explaining that it can “penetrate deep into the lungs and even enter the bloodstream, leading to a range of health problems.”

This includes respiratory issues such as asthma and chronic obstructive pulmonary disease, poorer lung function, as well as cardiovascular diseases like heart attacks and strokes. “Prolonged exposure is also associated with systemic inflammation and oxidative stress, which contribute to the development of chronic illnesses”, Aretz warned.

Current research increasingly points to fine particulate matter’s adverse effects on brain health, said Aretz.

“It has been implicated in neuroinflammation, disruption of the blood-brain barrier, and oxidative stress, all of which can lead to cognitive decline, memory impairment, and an increased risk of neurodegenerative diseases such as Alzheimer’s and Parkinson’s,” he said.

“These effects are particularly concerning for vulnerable populations, including the elderly and those with preexisting chronic diseases,” added Aretz.

Aretz was drawn to analysing air pollution and its effects on health as it connected to his doctoral thesis, during which he had already collaborated with the University of Luxembourg’s Professor Michael Heneka, the senior author in the current study. In his doctoral research, he partially examined PM2.5’s effect on cognitive performance, but observed a missing link.

The other important impetus for this research project for Aretz was therefore his desire to provide better understanding of the processes by which PM2.5 impacts our brain.

“Fine particulate matter represents the greatest environmental health burden, yet the mechanisms underlying its effects on brain health remain poorly understood,” said Aretz.

Deeper understanding is a crucial step “for developing effective interventions to mitigate cognitive impairment caused by fine particulate matter, particularly as the global population ages,” underlined Aretz.

Collaborative research process

The project eventually took shape not only as a collaboration between three universities – Luxembourg, Rostock and Aretz’s current university, in Bonn -but also between disciplines.

Such cooperation is “essential in health research to achieve the synergy needed to unravel its complexities,” said Aretz.

In this particular instance, teams from statistical modelling and neurology joined forces.

“Statisticians excel at developing and estimating empirical models, while neurologists contribute by conceptualising the study design and interpreting the observed effects leading to a comprehensive approach,” said Aretz.  

“As my former PhD supervisor, Professor Gabriele Doblhammer, once told me: A good paper is like a work of art. Such a paper often represents years of effort – starting with raw data, producing initial results, refining models and gaining even more statistical expertise, crafting the narrative, and ultimately creating a finished piece. Readers rarely see the immense sweat and labour behind it,” said Aretz.

The researchers used a method called causal pathway analysis to uncover how PM2.5 may be dangerous to humans, which Aretz describes as “a detective method that helps identify the steps or ‘pathways’ connecting cause – fine particulate matter – and effect – how well the brain works.”

This process led to their major finding that “exposure to fine particulate matter slows cognitive processing time,” partly due to an increase in white blood cell count. This suggests that PM2.5 affects the brain through systemic inflammation.

This could indicate a possible avenue for real-world approaches, which, according to Aretz, “include implementing policies to reduce PM2.5 exposure, targeting systemic inflammation through interventions, identifying high-risk populations via biomarkers, and addressing environmental inequalities to mitigate cognitive and health disparities.”

While this key finding was crucial in advancing an explanation of the link between brain health and air pollution, Aretz suggests further research in the field is needed.

“This should focus on understanding the molecular mechanisms by which systemic inflammation and monocytes mediate PM2.5’s impact on cognitive decline while exploring its relevance to other neurodegenerative diseases and the effects of prolonged exposure” said Aretz.

The University of Bonn academic has already begun work on a follow-up project, in collaboration with researchers from the University of Groningen in the Netherlands.

Together, the teams are investigating “the role of genetic variants in the pathways through which fine particulate matter affects cognitive function”.

“This research is crucial for identifying vulnerable subpopulations that may be particularly susceptible to the neurotoxic effects of fine particulate matter, thereby highlighting key health risks,” said Aretz.