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It has long been a consensus in the scientific community that air pollution is harmful to health. More and more studies have shown that air pollutants can not only cause respiratory and cardiovascular diseases, but their influence even extends to the brain: there is continuous evidence that air pollution is very likely to cause brain damage, induce neurodegenerative diseases and behavioral disorders.
How do air pollutants affect our brains?
Air pollutants, especially fine particulate matter (PM2.5) with a diameter of less than 2.5 micrometers, can escape the human body's protective system, including the pursuit of immune sentinel cells and the interception of biological barriers, and enter the human blood, heart tissue and even the placenta. However, the brain has a tight protective layer: the blood-brain barrier can keep foreign substances out of the brain. Logically speaking, fine particulate matter in the air should not be able to cross this barrier.
However, in a study published in the Proceedings of the National Academy of Sciences of the United States of America, an international collaborative team led by the Research Center for Eco-Environmental Sciences of the Chinese Academy of Sciences found direct evidence that air pollution enters the brain. Research indicates that the fine particulate matter we inhale can disrupt the blood-brain barrier through the bloodstream, invade the brain, and potentially cause damage to the nervous system.
To test whether fine particulate matter can enter the brain, the research team first used tools such as high-resolution transmission electron microscopes to conduct detailed tests on cerebrospinal fluid samples from 25 patients hospitalized due to brain dysfunction.
Cerebrospinal fluid surrounds and protects the entire brain, helping to remove metabolic waste and foreign components secreted by the brain. Therefore, if foreign particulate matter appears in the cerebrospinal fluid, it indicates that they have crossed the blood-brain barrier and entered the brain.
As a result, the research team detected foreign fine particulate matter in the samples of eight of the patients. These particles include common fine air particles such as calcium carbonate, iron-containing components (calcium iron oxide), and silicon-containing components (silicon dioxide). This discovery reminds us that these toxic particles can enter the brain and remain there.
Subsequently, in vitro and in vivo studies on mice further confirmed the way fine particulate matter enters the brain. According to these experiments, fine particulate matter inhaled into the lungs will first cross the barrier of qi and blood and enter the bloodstream. Subsequently, they follow the blood to the blood-brain barrier, where fine particles can damage the blood-brain barrier and surrounding tissues and enter the brain. Furthermore, isotope labeling experiments tell us that compared with other organs, fine particulate matter is more difficult to clear in the brain and can remain there for a longer time.
Previously, some studies speculated that fine particulate matter could directly enter the brain through the olfactory bulb, but the latest research has verified another more destructive pathway.
"Our data show that the amount of fine particulate matter that enters the brain through the bloodstream is eight times more than that directly through the nose," commented Professor Iseult Lynch of the University of Birmingham, a co-author of the paper. "There are still deficiencies in our understanding of the harm that fine particulate matter in the air causes to the central nervous system. This work demonstrates the connection between air pollution and brain damage and will reveal to us how inhaled particles move within our bodies."
In recent years, an increasing amount of evidence has demonstrated a strong correlation between air pollution and neuroinflammation, changes related to Alzheimer's disease, and cognitive problems. Such a relationship is not only present in the elderly, but even children are not spared. The conclusion of this latest research once again serves as a warning to us: If air pollution is allowed to worsen unchecked, it will be difficult for everyone to escape the risk of brain damage.
