Doubly harmful: fine dust is not only bad for our lungs, the air particles can also affect the health of our brain and lead to dementia. But why? As doctors have now discovered, particulate matter leads to local inflammation in the brain and also increases the number of certain white blood cells. The latter triggers systemic inflammation in the body, which also affects cognitive abilities and promotes neurodegenerative diseases.
Air pollution is often viewed as a health threat to our respiratory system. Fine dust – a complex mixture of many chemicals that occur in the air as fine particles with a maximum diameter of 2.5 micrometers (PM2.5) – is small enough to enter the lungs when inhaled and from there into the bloodstream. This can lead, among other things, to tissue damage and inflammation in the lungs.
Fine dust also plays a role in mental decline. Long-term exposure to air pollution has been shown to have a higher risk of developing neurodegenerative diseases such as Alzheimer’s or Parkinson’s. Because even a small amount of fine dust pollution impairs the ability to think. This also applies to younger adults and children, as recent studies suggest.
Why does particulate matter damage the brain?
But why is that? One reason: The tiny pollutant particles can cross the blood-brain barrier and trigger local inflammation in the brain. However, how fine dust particles influence cognitive functions in different age groups is still poorly understood.
A team led by Benjamin Aretz from the University Hospital of Bonn has now investigated this with the help of a broader group of test subjects. The doctors analyzed data from more than 66,000 participants in a Dutch health study. They compared the results of blood analyzes and cognitive tests carried out on the test subjects between 2006 and 2015 with data on air quality where they lived.
Connection with immune system proven
The result: People who were exposed to more PM2.5 particles at home had longer cognitive processing time (CPT) than people who inhaled less particulate matter. This measurement is a measure of how quickly the brain can react to stimuli. This means that the test subjects had become mentally slower due to the fine dust.
This effect also correlated with another measurement: the number of monocytes in the blood. These white blood cells are part of the immune system. People with high levels of particulate matter pollution and severe mental decline had more such monocytes. This is a sign that these people’s immune systems are fighting inflammation in the body.
Inflammation threatens mental health
The researchers conclude that air pollution leads to whole-body inflammation, which also affects mental abilities. “Systemic inflammation may act as an important mediator, linking PM2.5 exposure to impaired cognitive function,” says Aretz.
“It has already been shown that inflammation plays an important role in the development of neurodegenerative diseases. Therefore, the inflammation we see in response to air pollution can disrupt immune functions in the brain, thereby indirectly affecting cognitive health,” adds Doblhammer. A possible consequence of this brain damage could be Alzheimer’s dementia.
The culprit has not yet been identified
The study shows two different ways in which the brain breaks down under the influence of particulate matter: directly via local inflammation and indirectly via whole-body inflammation mediated by monocytes. In view of the aging population, these findings are important in order to specifically reduce fine dust and reduce the health risk it poses.
However, further data is still missing: “Given the strong correlation between air pollution and cognitive deficits, further studies are essential to find out which pollutants and cellular mechanisms mediate this effect,” says senior author Michael Heneka from the University of Luxembourg. (Alzheimer’s & Dementia, 2024; doi: 10.1002/alz.14320)
Source: University of Luxembourg
October 28, 2024 – Claudia Krapp
